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书书书
生物专业英语BiologyEnglish
李关荣 王贵学 主 编
西南师范大学出版社
图书在版编目(CIP)数据
生物专业英语/李关荣,王贵学主编.—重庆:西南师范大学
出版社,2007.9
ISBN9787562138785
Ⅰ.生… Ⅱ.李… Ⅲ.生物学—英语—高等学校—教材
Ⅳ.H31
中国版本图书馆CIP数据核字(2007)第076761号
生物专业英语李关荣 王贵学 主编
责任编辑:李 玲 杜珍辉
出版发行:西南师范大学出版社
地址:重庆市北碚区天生路1号
邮编:400715 市场营销部电话:023-68868624http://www.xscbs.com
经 销:全国新华书店
印 刷:西南农业大学印刷厂
开 本:787mm×1092mm 1/16印 张:10.5字 数:248千字
版 次:2007年9月 第1版
印 次:2007年9月 第1次印刷
书 号:ISBN 9787562138785
定 价:17.00元
书书书
前 言
《生物专业英语》是全国许多高等院校生物技术、生物科
学、生物工程及相关专业的必选课之一。它是在学生具有一
定的相关生物学基础知识上,通过学习相关的反映这些普通
生物学和现代生物学的基础知识的英文短文,掌握生物学基
本知识及其英文表述方法和特点,了解现代生命科学的发展
方向和研究前沿,进而提高对英文科技文章的阅读和理解、专
业英语表达以及英文科技论文的写作能力。
本书注重现代生物学发展趋势,兼顾继承和发展,正确处
理了经典生物学和现代生物学知识及生物学问题的关系,理
论联系实际。并考虑教学特点,拓宽学生的 生 物 学 基 础 知 识
面,兼顾生物学一级学科的主要分支,重点突出,脉络清晰。
本书是作者根据多年的专业英语教学经验和积累的大量
相关资料,经系统整理、修订而完成的。为保持专业英语的地
道性和 时 代 特 点,内 容 来 源 于 如 美 国 的《时 代 周 刊》、Leh
ningerPrinciplesofBiochemistry(DavidL.NelsonandMi
chaelM.CoxEds,2000,the3rdedition)以及国内外许多相
关学 习 网 站 等 多 种 媒 体,经 系 统 整 理 改 编,主 要 用 于 教 学 目
的。编者对相关人员和单位表示衷心的感谢。主要内容有动
物、植物、微生物及人体的结构、生理、生化及遗传等方面的基
础知识;分子生物学、遗传工程、克隆技术、转基因学与食品安
全、基因组学、蛋白组学和生物信息学等现代生物学知识前沿
及动态。本书基本覆盖了生物学一级学科的主要分支,可供
生物技术、生物科学、生物工程、农学等相关专业的学生和教
师使用。
全书共分13个单元:科技英语的概念及写作特点,细胞
结构和原生质的特性,生物化学,植物学及植物生理,遗传与
进化,人类解剖及生理,微生物,动物行为,食品、营养与健康,
分子生物学及转基因学,生物技术,基因组学和蛋白组学、生
物信息学基础。每 单 元 选 择 代 表 性 短 文1~7篇 以 上,共50
篇短文。短文中的专业词汇及疑难句子结构都编了号,便于
在随后的“Notes”部分查阅。专业词汇都给出了国际音标注
音和主要中文释义。
由于编者水平有限,现代生命科学发展迅猛,书中难免有
疏漏和不妥之处,望读者多提意见,以便再版时修订。
书书书
目录
1
UNIT01 THECONCEPTANDCHARACTERISTICSOFSCIENTIFICENGLISH
1 Essay01 TheConceptofEnglishforScienceandTechnology3 Essay02 MustWeWrite?
7 UNIT02 FEATURESOFCELLSANDPROTOPLASM7 Essay03 AnIntroductiontoCells9 Essay04 MajorStructuralFeaturesofEukaryoticCells18
Essay05 Colloids:CharacteristicComponentsofProtoplasmofAllCells
20 UNIT03 BIOCHEMISTRY20 Essay06 CellsandTissuesUsedinBiochemicalStudies22
Essay07 TheαHelixIsaCommonProteinSecondaryStructure
25 Essay08 DNAIsaDoubleHelix27 Essay09 ReactionsoftheCitricAcidCycle30 Essay10 BloodSubstitute
35 UNIT04 BOTANYANDPLANTPHYSIOLOGY35 Essay11 StomatalAnatomy36 Essay12 TheParadoxofPores38 Essay13 Osmosis40 Essay14 PrinciplesofPhotosyntheticEnergyTransformation44 Essay15 DesertPlantSurvival
48 UNIT05 GENETICSANDEVOLUTION48 Essay16 Mendel'sGeneticLaws51 Essay17 WhatIsaGeneticMap?
53 Essay18 BiologicalEvolution
57 UNIT06 HUMANANATOMYANDPHYSIOLOGY57 Essay19 TheHumanBrain58 Essay20 Diagnosis:Female
64 UNIT07 MICROBES64
Essay21 AgrobacteriumtumefaciensandItsUsesinPlantBreeding
67 Essay22 BacillusthuringiensisandItsUses72 Essay23 SomeFactsAboutE.coli
75 UNIT08 ANIMALBEHAVIOR75 Essay24 TheElephant77 Essay25 LivingTogether78 Essay26 CrazyOwnersMakeforCrazyPets79 Essay27 FishandSound82 Essay28 Animals’UsesofCryingandBegging83 Essay29 FrogCalls86 Essay30 Dolphins
91 UNIT09 FOOD,NUTRITIONANDHEALTH91 Essay31 Food93 Essay32 Vitamins95 Essay33 FoodsThatFightCancer
97 UNIT10 MOLECULARBIOLOGYANDTRANSGENICS97 Essay34 ThePolymeraseChainReaction(PCR),theBasics99 Essay35 MethodsofPlantGeneTransfer100 Essay36 GenesandMoney—PaternityTest102 Essay37 GeneGunSpeedsSearchforNewOrchidColors103
Essay38 PatentingGeneSequences:NotintheBestInterestsofScienceorSociety
107 UNIT11 BIOTECHNOLOGY107 Essay39 PlantTissueCulture111 Essay40 CloningTechniques113 Essay41 HowtoCloneaHerd?
114 Essay42 Clones:AsmanyTwinsAsYouLike!
115 Essay43 StemCellsandTheirUses120
Essay44 WhatIfMyTesttubeBabiesWereSwappedintheLab?
122 UNIT12 GENOMICSANDPROTEOMICS122 Essay45 Genomics124 Essay46 RiceGenomeWorkCreatesHope
126 Essay47ScientistsCrackGeneCodeofRice127 Essay48 GrainsofHope133 Essay49 Proteomics
136 UNIT13 Bioinformatics136 Essay50 Bioinformatics,theBasics
145 附录1 生物专业英语常见词素
149 附录2 生物专业英语常见词缀
书书书
1
犝犖犐犜01 犜犎犈犆犗犖犆犈犘犜犃犖犇犆犎犃犚犃犆犜犈犚犐犛犜犐犆犛犗犉犛犆犐犈犖犜犐犉犐犆犈犖犌犔犐犛犎
犈狊狊犪狔01 犜犺犲犆狅狀犮犲狆狋狅犳犈狀犵犾犻狊犺犳狅狉犛犮犻犲狀犮犲犪狀犱犜犲犮犺狀狅犾狅犵狔
1.Englishisagloballanguage.Withtheriseandrapidspreadingofelectroniccommunication,worldwidetradeandinternationaltravel,itsstatushasfarsurpassedthatofalinklanguage.Tosomeextent,Englishisequatedwithsuccess.Whereveryougo,fromtheluxuriantrainforestsofCostaRica[1]totheuntamedwildsofSerengeti[2]tothehodge
podge[3]ofEasternbazaars[4],you’resuretofindsomeonewhospeaksEnglishalbeit[5]
inanaccentfardifferentfromyours.Ifnothingelse,EnglishmakesadisguisedappearanceinhybridssuchasFranglais[6],Spanglish[7],Hindlish[8],Chinglish[9],etc.
2.NowadaysEnglishisestablishednotjustasthelinquafranka[10]oftheworldbutalsoastheinternationallanguageofscienceandtechnology.AnincreasingnumberofscientistsandtechniciansacrosstheworldareobligedtoreadanincreasingproportionofresearchpapersandtextbookswritteninscientificEnglish.OverthelastdecadesorsothetermEST,EnglishforScienceandTechnology,hasappearedfrequentlyinEnglishteachingrelatedliterature.
3.ThelanguageofESTthatexpressesscientificandtechnicalconcepts,theoriesandfactsisnotadifferentlanguagefromthatofthedailyconversationorliterature.But,duetoitsroleinscienceandtechnology,ESTcoversaspecialrangeofEnglish.Englishlan
guagelearnersrequireEnglishsoastopromotetheireducationalspecialtyortoperformefficientlytheirrolesasscientists,technologists,technicians,etc.AgeneralEnglishcanhardly meetsuchneedsasthese.Consequently,EnglishforSpecialPurposes(ESP)[11]hasemergedasabranchofEnglishlanguagestudy.
4.ESPconsistsofEAP[12](EnglishforAcademicPurposes),EOP[13](EnglishforOccupa
tionalorVocationalPurposes)andEST[14](EnglishforScienceandTechnology).EAPisusedbyoverseasstudents,researchersandvisitingscholarsatschoolsanduniversitiesinBritainandAmericaorinanyothercountrieswhereEnglishisusedincoursesandlectures;IntheUnitedStatesEOP(EnglishforOccupationalorVocationalPurposes)isalsocalled“EnglishforCareers”.ItistheEnglishnecessaryforsomeoccupationalrequirements,e.g.forinternationaltelephoneoperators,internationalairtrafficcontrollers,internationalcommerce,internationalrailways,computerprogramming,
tourismandsoon,orvocationaltrainingprograms,e.g.forhotelandcateringstaff,
technicaltrades,etc.
UNIT01 犜犎犈犆犗犖犆犈犘犜犃犖犇犆犎犃犚犃犆犜犈犚犐犛犜犐犆犛犗犉犛犆犐犈犖犜犐犉犐犆犈犖犌犔犐犛犎
2
5.Oureraistheageofmachines,electroniccomputersandeveradvancingbiology.Onlybyobtainingasolidknowledgeofscience,canonefunctionnormallyandsuccessfullyinmodernsociety.Withthedevelopmentofscienceandtechnology,especiallybiologyrelateddisciplines,scientistsandengineersstrivetoexchangetheirideas,discoveriesandinventions,collectinformationanddata,interpretconceptsandtheories,commentonthelatestscientificadvancesandwritereportsbasedonexperimentalprocedures,etc.Moreandmorescientifictermsfrommodernbiologysuchas,clone[15],GM[16](Genetically modified)foods,gene,genomics[17],proteomics[18],transgenics[19],DNAchips[20],etc.,arebecomingpopularized.Theneedincreasesdaybydayforscientistsandengineerstohaveaswift,economical,efficient,impersonalandsometimesinternationalmeansofcommunication.
6.However,ESTisnotthepopularizedaccountsofthetechnicalsubjectsasarefoundinencyclopedias[21]orbooksintendedforgeneralreaders.Ithasitsownauthentic[22]languageofscience!Lately,textbookshavebeenappearingthatattempttoreflectthenatureofthelanguageactuallyusedbyscientistsandthefunctionitserves.HoweversomepeoplestillignoretheexistenceofESTalltogether,whileothersarequiteindifferenttoit.Theydrawasimpleformulalikethis:EST=GeneralEnglishGrammar+TechnicalWords.TheythoughtthattheywouldbeabletounderstandESTbysimplyknowinggrammaticalrulesinadditiontosometechnicalwords.
7.Unfortunately,thisjudgmentgivesnofruitfulcomprehensionaboutthenatureofEST.TheydonotseemtobeawarethatESTpresentslinguisticvarietieswithitsowncharacteristicfeatures.
8.Sincescientiststrytobeimpersonalinnarratingthenaturalphenomenaandfacts,theirprocesses,propertiesandcharacteristics,EnglishforScienceandTechnology(EST)
mustbeevidentlyprecise,concise,clearandrestrictedandincludesmanymathematicalequations,formulae,diagrams,tables,etc.Biologyrelatedpublicationsaremoresoever.Scientistsalsoprefersometypicalsentencepatternsandalargenumberoftechnicalandsemitechnicalterms,whichmakeEnglishforScienceandTechnologydifferenttoaverywideextentfromordinaryEnglish.
Notes
[1]CostaRica[5kRstE5ri:kE]n.哥斯达
黎加
[2]Serengeti[siren`giti]n.塞伦盖提
[3]hodgepodge[5hRdVpCdV]n.大杂烩
[4]bazaar[bE5zB:]n.集市,闹市
[5]albeit[C:l5bi:it]adv.虽然
[6]Franglais[frB:n5glei]n.(法语中的)
英语外来语
[7]Spanglish[5spAnliF]n.混有 西 班 牙
文英语
[8]Hindlish[hindliF]n.混有印度语的英语
[9]Chinglish[tFin^liF]n.混有 中 文 的 英
语
[10]linquafranka[5liN^ w[5frANk[]n.
3
通用语,混合语
[11]ESP:EnglishforSpecialPurposes特
殊用途英语
[12]EAP:EnglishforAcademic[7AkE5demik]Purposes学术用途英语
[13] EOP: English for Occupational[7Rkju5peiF[n[l]orVocational[vEu5keiF[n[l]Purposes职业英语
[14]EST:EnglishforScienceandTechnology科技英语
[15]clone[kl[un]n.克隆
[16]GM (Geneticallymodified)food遗传
修饰食品
[17]genomics[`dVi:n[Umiks]n.基 因 组
学
[18]proteomics[`pr[uti[umiks]n.蛋白组
学
[19]transgenics[trAns5dVeniks]n.转基
因学
[20]DNAchip[tFip]DNA芯片
[21]encyclopedia[en7sBikl[u5pi:di[]n.百科全书
[22]authentic[R:5Wentik]adj.真 实 可
信的
犈狊狊犪狔02 犕狌狊狋犠犲犠狉犻狋犲?
1.Manynewfindingsanddiscoveriesaredocumentedwithreferencestothescientificliterature,indicatedbythenamesoftheauthor(s)andtheyearofpublication.Publication,
asitturnsout,isanabsolutelyessentialpartofthescientificprogress,asPageMorganexplainsinthisessay.Dr.MorganisaProfessorofPlantPhysiologyintheDepartmentofSoilandCropScienceatTexasA&MUniversity.Formanyyears,hehasalsobeenanAssociateEditor(forplantdevelopmentandgrowthregulators)ofthejournalPlantPhysiology.Prof.Morgantellsushowthesystemworksandgivesafewpointerstomanuscriptpreparationforthescientificliterature.
2.Scientistsmustwrite!Knowledgeuncommunicatediseffectivelyunknown;discoveryisbutonesteponthepathofunderstanding.Althoughyoumayagreewiththesestatements,youmaynotbeawarehowoftenscientistsandsciencestudents[1]arepoorly
preparedtowrite.Aregenesforwriters’block[2]linkedtothoseforinvestigativetalent?Probablynot,butwhileastudentisstudyingtheconceptsofscience,practicingitstechniques,andlearningitsliterature,itmaybedifficulttofindthetimetodevelopgoodcommunicationsskills.Theseskillstakepracticetodevelop.Educatorssoonlearnthatmanystudentshatetowrite.Givenmyexperienceinteaching,advisinggraduatestudents,andservingasadecisioneditor[3]forascientificjournal,Iwouldliketodiscusswritingwiththereadersofthistext.
3.Thefirstpointisthatwritingisnecessary.Asayoungfaculty[4]memberIremember
hearingourDean[5]say,“Researchisnotcompleteduntilitispublished.”Hewasright.Studentsmustultimatelywritewhattheyhavediscoveredorlearned.Quizzes,
reports,termpapers,theses,anddissertations[6]allowotherstoknowandjudgeyour
UNIT01 犜犎犈犆犗犖犆犈犘犜犃犖犇犆犎犃犚犃犆犜犈犚犐犛犜犐犆犛犗犉犛犆犐犈犖犜犐犉犐犆犈犖犌犔犐犛犎
4
abilityandaccomplishments.Studentswhofollowascientificcareersoonareinvolvedinwrittencommunications:justifications[7]forequipmentpurchases,courseoutlines,
researchfundingproposals,andmanuscriptsreportingresearchfindings.Reviewarticles[8],booksandpiecesforthesemipopular[9]press,flowfromthepens(orcomputerkeyboards)ofthemoreprolific[10].Writingisessentialinscience!
4.Thisdiscussionisnottoadvocates“PublishorPerish[11]”,butrather“PublishorNoOneWillKnow.”Untilyoumentallywrestlewith[12]aquestionandwritedownyourbestanswer,yourinstructorcannotevaluatehowwellyouhavelearned.Likewise,untilscientistshavepublishedtheresultsandconclusionsfromtheirexperiments,nooneelsecanevaluate[13]thesignificanceandusefulnessofthework.Onlyafternewfactsandideasarepublished,discussed,andreplicated[14]byfurthertestingcanthevalidonesultimatelycontributetoadvancingunderstandinginscienceasawhole.
5.Unfortunately,it’snotenoughtowrite;theneedistowritewell.Considertwostudentswhospendhoursinthelibraryresearchingthesametermpapertopic.Equallywellversed[15]inthefacts,onewritesanuninspired[16],cataloglikelistingofwhodidwhatandwhen.Thesecondstudentidentifiestherelevantquestions,arraysthefactstosupportlogicaldeductions[17],andbringsthetopictoasharplyfocusedconclusion.Onewroteandtheotherwrotewell.Attheprofessionalleveltheobjectiveforwritingascientificpaperisnottogetitpublished,butrathertocommunicatewithotherscientists.Everyonehasalimitedamountoftime.Writersareliterally[18]competingforthetimeandattentionofpotentialreaders.Regardlessofhowimportantadiscoveryis,itwillusuallybemorerapidlyacceptedifitispresentedinawellwrittenpaper.Ontheotherhand,ifthewritingispoorandthemessageobscure,readerswilloftenquitbeforecompletingthepaper.
6.Perhapssome“do’s”and“don’ts”wouldbehelpful.Mostinstructorshaveseenalotofbadwriting;thus,the“don’ts”areeasytolist.Inmyexperience,themostcommonerroristhatwritersfailtoclearlystatetheirmessage.Thereaderwonders:whatdowelearnaboutplantphysiologyfromtheexperiment?Isitneworunique?Isituseful?Thestudentwritingalabreport[19]orthescientistwritingforajournalhastheresponsibilitytoanswerthosequestions.Anothercommonerroroccurswhenamanuscriptappearstobeapartiallycondensedthesis.Themessageislostinwordiness[20]andsecondarytopics,anda10pagestorygetstoldin25.Also,thetechnicallanguageofexperimentaldesignandstatisticsisoftenusedasawritingcrutch[21];Asaresult,clarity[22]suffers.Readersareusuallyinterestedinwhattheresponsewas,anditsmagnitude,variability,
andreproducibility.Jargon[23]about“significantthreewayinteractionsincompletefactorials”promptsdrowsiness.
7.Anothercommonwritingerroriscarelesspreparation.Mostwritingtasks,whethersomethingassimpleasanessayexaminationorascomplicatedasreviewedjournalmanuscript,includinginstructions.Yettimeaftertimewritersappeartoignoretheinstructionsandsubmitcarelesslypreparedmaterial.Theaxiom[24]“Younevergetasecond
5
chancetomakeagoodfirstimpression”certainlyappliestowriting.Althoughtechnicalaspectsofcompositionarebeyondthescopeofthisessay,studentswouldbewellservedtodevelopthehabitofreviewingtheirwritingforspelling,punctuation,andsentencestructurebeforeitissubmittedtoothers.Writinghandbookslistthecommonmistakes,suchasusingwhichinplaceofthat.Equipyourselfwithagoodwritinghandbookandadictionary,andusethem!
8.Thepositivesuggestionsforscientificwritingmuststartwiththescientificmethod.Thereisnosubstituteforexpressingthetopicasaquestionthatcanbeanswered.Searchingoutwhatisalreadyknownisequallyindispensable[25].Ifawritersitsdowntowrite,forexample,aboutsometopicasbroadas“tissueculturestudieswithsoybeans,”orifawriterdismissesrelevantbackgroundknowledgewithwordssuchas“littleisknownaboutthissubject”,thepapermayalreadybeunsalvageable.Writersshouldhavetheprimarymessageoftheirpapersinmindbeforetheywritethefirstword.Thatmessage,infact,shouldbeananswertoaclearlystatedquestion,anditshouldshapethetitle,theintroduction,andthebodyofthepaper.Inthatwayreaderscanrecognizeatheme[26]thatisconsistentthroughoutthepaper.
9.Thepurposeofscientificwritingistocommunicatefindings,analyses,conclusions,andtheories.Communicateistheoperative[27]word.Unlessthereaderunderstands,thewriterhasfailed.Theimplications[28]areobvious:Identifytheaudienceandwritetothatlevelofunderstanding.Clarityisofteninverselyrelatedtosentencelength.Abarrage[29]ofwordswithobscuremeaningsmakesreadingachore[30]ratherthanapleasure.Thewordsselectedshouldaidcommunicationratherthanmakeastatementaboutthewriter’svocabulary.Sentencesthatcanbemisunderstoodusuallywillbe.Brevity[31]isavirtuewhenwedtoclarity.Writersshouldwriteinadirect,simple,logicalstyle;therewardisbeingreadandbeingunderstood.
10.Writersshouldgiveseriousattentiontographicillustration.Pooronesfrequentlyappeartobeanafterthought[32].Excellentillustrationsoffindingsorconclusionsareoftenthemosteffectivewaytocommunicate.Thesayingthat“Onepictureisworthathousandwords”makesthatpoint.Goodillustrationsdon’tjusthappen;theytaketheforethought[33],inventivenessandwork.Wetraingraduatestudentstogiveseminarswithmuchemphasisongoodslides.Thatemphasisisintendedtocarryoverintotheirwrittencommunications.Computergraphicsmakethejobeasier,butthebottomlineisstillpersonalinitiative[34].
11.Inconclusion,theabilitytowritewellisaskillneededbysciencestudentsandscientistsalike.Itcanbeacquiredandcultivatedifthebasicgoalofcommunicationiskeptclearlyinview.Thosewhocanthinkandspeaklogicallycanlearntowritelogically,andeveninterestinglyandentertainingly.Sciencewillbethebetterforsuchwriting!
UNIT01 犜犎犈犆犗犖犆犈犘犜犃犖犇犆犎犃犚犃犆犜犈犚犐犛犜犐犆犛犗犉犛犆犐犈犖犜犐犉犐犆犈犖犌犔犐犛犎
6
Notes
[1]sciencestudentn.理科学生
[2]blockn.(俚语)脑袋
[3]decisioneditor[di5siV[n5edit[]决策
编辑
[4]faculty[5fAk[lti]n.全体教员
[5]Dean[di:n]n.大学院长,系主任
[6]dissertation[9dis[5teiF[n]n.(学位)论文,专题,论述,学术演讲
[7]justification[dVQstifi5keiF[n]n.认
为有理,认为正当,理由,辩护,释罪
[8]reviewarticlen.综述文章
[9]semipopularadj.半科普的
[10]prolific[pr[5lifik]adj.多产的,丰富
的,大量繁殖的
[11]perish[`periF]vi.毁灭,死亡,腐烂,枯萎vt.毁坏,使麻木
[12]wrestle[5resl]withvi.与……搏斗
[13]evaluate[i5vAljueit]vt.评 价,估 计,求……的值v.评价
[14]replicate[`replikit]v.复制
[15]versed[v[:st]adj.熟练的,精通的
[16]uninspired [`Qnin5spai[d]adj.未 赋
予灵感的,缺乏创见的,平凡的
[17]deduction[di`dQkF[n]n.缩 小,减
小,扣除,折扣,扣 除 额,折 扣 额,推
论,演绎法
[18]literally[`lit[r[li]adv.照 字 面 意 义,
逐字地
[19]labreport实验报告
[20]wordiness[`w[:dines]n.多嘴,冗长
[21]crutch[krQtF]n.(跛 子 用 的)拐 杖,支撑,帮助
[22]clarity[5lAriti]n.清楚,透明
[23]jargon[`dVB:g[n]n.行话
[24]axiom [`Aksi[m]n.公 理,自 明 之 理:不言而喻的或普遍被认定的真理;格言
[25]indispensable[9indis5pens[bl]adj.不可缺少的,绝对必要的
[26]theme[Wi:m]n.(谈 话,写 作 等 的)题目,主题
[27]operative[`Rp[r[tiv]adj.有效的;有
力量的;行动的,实用的
[28]implication[9impli`keiFEn]n.牵 连,纠缠,含蓄,含意,暗示
[29]barrage[`bArB:V]n.拦河坝,堰,阻
塞,(敌军前进的)弹幕射击
[30]chore[tFR:]n.家务琐事
[31]brevity[5breviti]n.(时间)短暂,(讲话,文章等)简短
[32]afterthought[`B:ft[WR:t]n.事后产
生的想法,追悔,再思
[33]forethought[`fR:WC:t]n.深谋远虑,先见
[34]initiative[i`niF[tiv]n.主动性
7
犝犖犐犜02 犉犈犃犜犝犚犈犛犗犉犆犈犔犔犛犃犖犇犘犚犗犜犗犘犔犃犛犕
犈狊狊犪狔03 犃狀犐狀狋狉狅犱狌犮狋犻狅狀狋狅犆犲犾犾狊
1.Cellsarethestructuralandfunctionalunitsofalllivingorganisms.Thesmallestorganismsconsistofsinglecellsandaremicroscopic,whereaslargerorganismsaremulticellular[1].Thehumanbody,forexample,containsatleast1014cells.Unicellular[2]or
ganismsarefoundingreatvarietiesthroughoutvirtuallyeveryenvironmentfromAntarcticatohotspringstotheinnerrecesses[3]oflargerorganisms.Multicellularorganismscontainmanydifferenttypesofcells,whichvaryinsize,shape,andspecializedfunction.Yetnomatterhowlargeandcomplextheorganism,eachofitscellsretainssomeindividualityandindependence.
2.Despitetheirmanydifferences,cellsofallkindssharecertainstructuralfeatures.The
plasmamembrane[4]definestheperiphery[5]ofthecell,separatingitscontentsfromthesurroundings.Itiscomposedofenormousnumbersoflipidandproteinmolecules,heldtogetherprimarilybynoncovalenthydrophobicinteractions[6],formingathin,tough,
pliable,hydrophobiclayeraroundthecell.Themembraneisabarriertothefreepassageofinorganicionsandmostotherchargedorpolarcompounds.Transportproteins[7]intheplasmamembraneallowthepassageofcertainionsandmolecules.Othermembraneproteinsincludereceptors[8]thattransmitsignalsfromtheoutsidetotheinsideofthecellandenzymes[9]thatparticipateinmembraneassociatedreactionpathways.
3.Becausetheindividuallipidsandproteinsoftheplasmamembranearenotcovalentlylinked,theentirestructureisremarkablyflexible,allowingchangesintheshapeandsizeofthecell.Asacellgrows,newlymadelipidandproteinmoleculesareinsertedintoitsplasmamembrane;celldivision[10]producestwocells,eachwithitsownmembrane.Growthandfissionoccurwithoutlossofmembraneintegrity[11].Inareversalofthefissionprocess,twoseparatemembranesurfacescanfuse,alsowithoutlossofintegrity.Membranefusionandfissionarecentraltomechanismsoftransportintoandoutofthecellsknownasendocytosis[12]andexocytosis[13],respectively.
4.Theinternalvolumeboundedbytheplasmamembrane,thecytoplasm[14],iscomposedofanaqueoussolution,thecytosol[15],andavarietyofinsoluble,suspendedparticles.Thecytosolisahighlyconcentratedaqueoussolutionwithacomplexcompositionand
gellikeconsistency.DissolvedinthecytosolaremanyenzymesandtheRNAmolecules
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thatencode[16]them,themonomericsubunits[17](aminoacids[18]andnucleotides[19])
fromwhichthesemacromolecules[20]areassembled,hundredsofsmallorganicmoleculescalledmetabolites[21],intermediatesinbiosyntheticanddegradativepathways,enzymes[22]thatareessentialparticipantsinmanyenzymecatalyzedreactions,andinorganicions.
5.Amongtheparticlessuspendedinthecytosolaresupramolecularcomplexes[23]and,inalmostallnonbacterialcells,avarietyofmembraneboundedorganelles[24]containingspecializedmetabolicmachinery.Ribosomes[25],smallparticles18to22nmindiameter,thatarecomposedofover50differentproteinandRNAmolecules,arethesitesatwhichproteinsynthesisoccurs.Ribosomesengagedinproteinsynthesisoftenoccurinclusterscalledpolysomes(polyribosomes)[26]heldtogetherbyastrandofmessengerRNA.Alsopresentinthecytoplasmofmanycellsaregranulesordropletscontainingstorednutrientssuchasstarchandfat.
6.Alllivingcellshave,foratleastsomepartoftheirlife,eitheranucleus[27]oranucleoid[28],inwhichthegenome[29](thecompletesetofgenescomposedofDNA)isstoredandreplicated.TheDNAmoleculesarealwaysfarlongerthanthecellsthemselvesandaretightlyfoldedandpackedwithinthenucleusornucleoidassupramolecularcomplexesofDNAwithspecificproteins.Thebacterialnucleiodisnotseparatedfromthecytoplasmbyamembrane,butinhigherorganismsthenuclearmaterialisenclosedwithinadoublemembrane,thenuclearenvelope[30].Cellswithnuclearenvelopesarecalledeukaryotes[31](Greekeu,“true”,andKaryon,nucleus);thosewithoutnuclearenvelopsbacterialcellsareprokaryotes[32](Greekpro,‘before’).
7.Unlikebacteria,eukaryoteshaveavarietyofothermembraneboundedorganellesintheircytoplasm,includingmitochondria[33],endoplasmicreticulum[34],Golgicomplexes[35],lysosomes[36]andvacuoles[37](relatedorganellesfoundinanimalandplantcells,
respectively),and,inphotosyntheticcells,chloroplasts[38].
Notes
[1]multicellular[7mQlti`seljul[]adj.多
细胞的
[2]unicellular[`ju:ni`seljul[]adj.单细胞
的
[3]recess[ri`ses]n.(墙壁等的)凹进处,[解]隐窝
[4]plasmamembrane [`plAzm[` membrein]n.质膜
[5]periphery[p[`rif[ri]n.外围
[6]noncovalenthydrophobicinteraction
[7nQnkEU`veil[nt7hBidr[J`f[Jbik9int[r`AkF[n]非共价键疏水相互作用
[7]transportproteinn.转运蛋白
[8]receptorsn.受体
[9]enzyme[`enzaim]n.酶
[10]celldivisionn.细胞分裂
[11]membraneintegrity[`membreinin`tegriti]n.膜的完整性
[12]endocytosis[9end[usBi`t[usis]n.(细
胞)内吞作用
9
[13]exocytosis[9eks[usai`t[usis]n.胞外
分泌
[14]cytoplasm [`sait[uplAzm]n.(细)胞质
[15]cytosol[`sait[usCl]n.(细)胞浆
[16]encode[in5k[ud]vt.编码
[17]monomericsubunit [7mRn[`meriksQb5jU:nit]n.单体亚单位
[18]aminoacid[5Amin[U` Asid]氨基酸
[19]nucleotide[`njU:kli[taid]n.核苷酸
[20]macromolecule[9mAkr[U`mRlikju:l]
n.大分子,高分子
[21]metabolite[mi`tAb[lait]n.代谢物
[22]coenzyme[k[U`enzaim]]n.辅酶
[23]supramolecularcomplex[9sjU:pr[m[`
lekjul[`kRmpleks]超分子复合物
[24]organelle[9C:g[`nel]n.细胞器
[25]ribosome[`raib[s[um]n.核糖体
[26]polysome[`pRlis[um](polyribosome)[9pRli`raib[s[um]n.多核糖体
[27]nucleus[`njU:kli[s]n.细胞核,核[28]nucleoid[`njU:kliRid]n.类核
[29]genome[`dVi:n[Um]n.基因组
[30]nuclearenvelope[`njU:kli[`envil[Up]
n.核膜
[31]eukaryote[ju`kAri[ut]n.真核细胞
[32]prokaryote[pr[U`kAri[ut]n.原核细
胞
[33]mitochondrion[9mait[`kRndri[n]n.线 粒 体(sing.)mitochondria[9mait[`
kRndri[]线粒体(pl)[34]endoplasmicreticulum [`end[u9plAzmik
ri`tikjul[m]n.内质网
[35]Golgicomplex [`gC:ldVi`kRmpleks]
n.高尔基复合体
[36]lysosome[`lais[s[Um]n.溶酶体
[37]vacuole[`vAkju[ul]n.液泡
[38]chloroplast[`klCr[plB:st]n.叶绿体
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1.Typicaleukaryoticcellsaremuchlargerthanprokaryoticcells—commonly5to100μmindiameter,withcellvolumesathousandtoamilliontimeslargerthanthoseofbacteria.Thedistinguishingcharacteristicofeukaryotesisthenucleus,whichhasacomplexinternalstructuresurroundedbyadoublemembrane.Anotherstrikingdifferencebetweeneukaryotesandprokaryotesisthateukaryotescontainanumberofothermembraneboundedorganelles.Thefollowingdescribethestructuresandrolesofthecom
ponentsofeukaryoticcellsinmoredetail.
ThePlasmaMembraneContainsTransportersandReceptors2.Theexternalsurfaceofacellisincontactwithothercells,theextracellular[1]fluid,andthesolutes,nutrientmolecules,hormones[2],neurotransmitters[3],andantigens[4]inthatfluid.Theplasmamembranesofallcellscontainmanytransporters,proteinsthatspanthemembraneandcarrynutrientsintothecellandvariousproductsout.Cellsalsohavesurfacemembraneproteins(signalreceptors[5])withhighlyspecificbindingsitesforextracellularsignalingmolecules(receptorligands[6]).Whenanexternalligandbindstoitsspecificreceptor,thereceptorproteintransducesthesignalcarriedbythat
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ligandintoanintracellular[7]message.Forexample,somesurfacereceptorsareassociatedwithionchannels[8]thatopenwhenthereceptorisoccupied,permittingentryofspecificions;othersactivateorinhibitcellularenzymesontheinnermembranesurface.Whateverthemodeofsignaltransduction,surfacereceptorscharacteristicallyactassignalamplifiers-asingleligandmoleculeboundtoasinglereceptormaycausethefluxofthousandsofionsthruanopenedchannelorthesynthesisofthousandsofmoleculesofanintracellularmessengermoleculebyanactivatedenzyme.
3.Somesurfacereceptorsrecognizeligandsoflowmolecularweight,andothersrecognizemacromolecules.ForExample,bindingofacetylcholine[9](Mr=146)toitsreceptorbe
ginsacascade[10]ofcellulareventsthatunderliethetransmissionofsignalsformusclecontraction.Bloodproteins(Mr>20,000)thatcarrylipids(lipoproteins[11])arerecognizesbyspecificcellsurfacereceptors,whichmediatelipidentryintothecells.Antigens(proteins,viruses,orbacteria,recognizedbytheimmunesystemasforeign)bindtospecificreceptorsandtriggertheproductionofantibodies[12].Duringthedevelopmentofmulticellularorganisms,neighboringcellsinfluenceeachother’sdevelopmentalpaths,assignalmoleculesfromonecelltypereactwithreceptorsofothercells.Thusthesurfacemembraneofacellisacomplexmosaic[13]ofdifferentkindsofhighlyspecific“molecularantennae”[14]thruwhichcellsreceive,amplify,andreacttoexternalsignals.
4.Mostcellsofhigherplantshaveacellwalloutsidetheplasmamembrane,whichserveasarigid,protectiveshell.Thecellwall,composedofcellulose[15]andothercarbohydratepolymers,isthickbutporous.Itallowswaterandsmallmoleculestopassreadily,butswellingofthecellduetotheaccumulationofwaterisresistedbytherigidityofthewall.
EndocytosisandExocytosisCarryTrafficacrossthePlasmaMembrane5.Endocytosisisamechanismfortransportingcomponentsofthesurroundingmediumdeepintothecytoplasm.Inthisprocess,aregionoftheplasmamembraneinvaginates[16],enclosingasmallvolumeofextracellularfluidwithinabudthatpinchesoffinsidethecellbymembranefission.Theresultingsmallvesicle[17](endosome[18])canmoveintointeriorofthecell,deliveringitscontentstoanotherorganelleboundedbyasinglemembrane(alysosome,forexample)byfusionofthemembranes.Theendosomethusservesasanintracellularextensionoftheplasmamembrane,effectivelyallowingintimatecontactbetweencomponentsoftheextracellularmediumandregionsdeepwithinthecytoplasm,whichcouldnotbereachedbydiffusionalone.Phagocytosis[19]isaspecialcaseofendocytosisinwhichthematerialcarriedintothecell(withinaphagosome[20])isparticulate[21],suchasacellfragmentorevenanother,smallercell.Theinverseofendocytosisisexocytosis,inwhichavesicleinthecytoplasmmovestotheinsidesurfaceoftheplasmamembrane.Manyproteinsdestinedforsecretionintotheextracellularspacearepackagedintovesiclescalledsecretorygranulesthenreleasedbyex
11
ocytosis.
TheEndoplasmicReticulumOrganizestheSynthesisofProteinsandLipids6.Thesmalltransportvesiclesmovingtoandfromontheplasmamembraneinexocytosisandendocytosisarepartsofadynamicsystemofintracellularmembranesthatincludestheendoplasmicreticulum,theGolgicomplex,thenuclearenvelope,andavarietyofsmallvesiclesaslysosomesandperoxisomes[22].Althoughgenerallyrepresentedasdiscreteandstaticelements,thesestructuresareinfactinconstantflux,withmembranevesiclescontinuallybuddingoff,movingthrough,andmergingwithmembranousstructureselsewhere.
7.Theendoplasmicreticulum(ER)isahighlyconvoluted[23],threedimensionalnetworkofmembraneenclosedspacesextendingthroughoutthecytoplasmandenclosingasubcellularcompartment[24](thelumen[25]oftheER)separatefromthecytoplasm.Themanyflattenedbranches(cisternae[26])ofthiscompartmentarecontinuouswitheachotherandwiththenuclearenvelope.Incellsspecializedforthesecretionofproteins,
suchasthepancreatic[27]cellsthatsecretethehormoneinsulin[28],theERisparticularlyprominent.Theribosomesthatsynthesizeproteinsdestinedforexportattachtotheouter(cytoplasmic)surfaceoftheER,andthesecretoryproteinsarepassedthroughthemembraneintothelumenastheyaresynthesized.DigestiveenzymesthatwillbesequesteredwithinlysosomesorproteinsdestinedforinsertionintothenuclearorplasmamembranesarealsosynthesizedonribosmesattachedtotheER.Bycontrast,proteinsthatwillremainandfunctionwithinthecytosolaresynthesizedoncytoplasmicribosomesunassociatedwiththeER.
8.Theattachmentofthousandsofribosomes(usuallyinregionsoflargecisternae)givestheroughendoplasmicreticulum(ER)[29]itsgranularappearanceandthusitsname.Inotherregionsofthecell,theERisfreeofribosomes.Thissmoothendoplasmicreticulum[30],whichisphysicallycontinuouswiththeroughER,isthesiteoflipidbiosynthesisandavarietyofotherimportantprocesses,includingthemetabolismofcertaindrugsandtoxiccompounds.SmoothERisgenerallytubular[31],incontrasttothelong,
flattenedcisternaetypicalofroughER.Insometissues(skeletalmuscle[32],forexample),theERisspecializedforthestorageandrapidreleaseofcalciumions.ReleaseofCa2+isthetriggerformanycellularevents,includingmusclecontraction.
TheGolgiComplexProcessesandSorts[33]Proteins9.NearlyalleukaryoticcellshaveGolgicomplexes,systemsofmembranoussacs,orcisternae,arrangedasflattenedstacks.Namedafteritsdiscoverer,CamilloGolgi,theGolgicomplexisasymmetric[34],structurallyandfunctionally.Thecisside[35]facestheroughER(andthenucleus),andthetransside[36]facestheplasmamembrane;betweenthesearethemedialelements.Proteins,duringtheirsynthesisonribosomesboundtotheroughER,areinsertedintotheinterior(lumen)oftheERcisternae.Smallmem
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branevesiclescontainingthenewlysynthesizedproteinsbud[37]fromtheERandmovetotheGolgicomplex,fusingwiththecisside.AstheproteinspassthrutheGolgicomplextothetransside,enzymesinthecomplexmodifytheproteinmoleculesbyaddingsulfate,carbohydrate,orlipidmoieties[38]tothesidechainsofcertainaminoacids.Oneofthefunctionsofthemodificationofanewlysynthesizedproteinisto“address”ittoitsproperdestinationasitleavestheGolgicomplexinatransportvesiclebuddingfromthetransside.Certainproteinsareenclosedinsecretorygranules[39],eventuallytobereleasedfromthecellbyexocytosis.Othersaretargetedforintracellularorganellessuchaslysosomesorforincorporationintotheplasmamembraneduringcellgrowth.
LysosomesAretheSitesofDegradativeReactions10.Lysosomes[40],foundonlyinanimalcells,aresphericalvesiclesboundedbyasingle
membranebilayer.Theyareusuallyabout1μmindiameter.Lysosomescontainenzymescapableofdigestingproteins,polysaccharides[41],nucleicacids[42],andlipids.Theyfunctionascellularrecyclingcenters[43],breakingdowncomplex moleculesbroughtintothecellbyendocytosis,fragmentsofforeigncellsbroughtinbyphagocytosis,orwornoutorganellesfromthecell’sowncytoplasm.Thesematerialsselectivelyenterthelysosomebyfusionofthelysosomalmembranewithendosomes,phagosomes,ordefectiveorganelles,andarethendegradedtotheirsimplecomponents(aminoacids,monosaccharides[44],fattyacids,etc.),whicharereleasedintothecytosoltoberecycledintonewcellularcomponentsorfurthercatabolized[45].
11.Thedegradativeenzymeswithinalysosomewouldbefreetoactonallcellularcomponentsweretheynotconfinedbythelysosomalmembrane.AsecondlineofdefenseagainstunwanteddestructionofcytosolicmacromoleculesbylysosomalenzymesisthedifferenceinpHbetweenthelysosomeandthecytosol,maintainedbytheactionofanATPfueledprotonpump[46]inthelysosomalmembrane.Thelysosomalcompartmentismoreacidic(pH5)thanthecytosol(pH≈7),andlysosomalenzymesaremuchlessactiveatthehigherpHofthecytosol.
VacuoleofPlantCellsPlaySeveralImportantRoles12.Plantcellsdonothavelysosomes,buttheirvacuolescarryoutsimilardegradativereactionsaswellasotherfunctionsfoundinanimalcells.Growingplantcellscontainseveralsmallvacuoles,vesiclesboundedbyasinglemembranebilayer.Asthecellmatures,
thevacuolesfuseandbecomeonelargecentralvacuole[47].Thevacuolemayrepresentasmuchas90%ofthetotalcellvolumeinamaturecell,pressingthecytoplasmintoathinlayerbetweenthevacuoleandtheplasmamembrane.Themembranesurroundingthevacuole,calledthetonoplast[48],regulatestheentryofions,metabolites,andcellularstructuresdestinedfordegradation,andtheliquidwithinthevacuolecontainsdigestiveenzymesthatdegradeandrecyclemacromolecularcomponents.Asinthelysosome,thepHwithinthevacuoleisgenerallylowerthanthepHofthesurroundingcytosol.In
13
someplantcells,thevacuolecontainshighconcentrationsofpigments (anthocyanins[49])thatgivesflowersandfruitstheirdeeppurpleandredcolors.Inadditiontoitsroleinstorageanddegradationofcellularcomponents,thevacuolealsoprovidesphysicalsupporttotheplantcell.Becausetheconcentrationofsolutes(salts,ions,degradationproducts)isgreaterinthevacuolethaninthecytosol,waterpassesosmotically[50]
intothevacuole,establishing,atequilibrium,anoutwardturgorpressure[51]onthecytoplasmandthecellwallthatstiffenstheplanttissue.
PeroxisomesDestroyHydrogenPeroxide[52]andGlyoxysomes[53]ConvertFatstoCarbohydrates13.Someoftheoxidativereactionsinthebreakdownofaminoacidsandfatsproducefree
radicals[54]andhydrogenperoxide(H2O2),veryactivechemicalspeciesthatcoulddamagecellularmachinery.Toprotectthecellfromthesedestructivebyproducts,suchreactionsaresegregatedwithinsmallmembraneboundedvesiclescalledperoxisome.Thehydrogenperoxideisdegradedbycatalase[55],anenzymepresentathighconcentrationinperoxisomes;itcatalyzesthereaction:
2H2O →2 2H2O+ O2Glyoxysomesarespecializedperoxisomesfoundincertainplantcells.Theycontainhighconcentrationsoftheenzymesoftheglyoxylatecycle[56],ametabolicpathwayuniquetoplantsthatconvertsstoredfatstocarbohydratesduringseedgermination.Lysosomes,
peroxisomes,andglyoxysomesaresometimesreferredtocollectivelyasmicrobodies[57].
TheNucleusContainstheGenome14.Theeukaryoticnucleusisquitecomplexinstructureandbiologicalactivitycompared
withtherelativelysimplenucleoidofprokaryotes.Thenucleuscontainsallacell’sDNA,whichcanbethousandsoftimesmorethanispresentinabacterialcell;asmallamountofDNAisalsopresentinmitochondriaandchloroplasts.Thenucleusissurroundedbyanuclearenvelope,composedoftwomembranebilayersseparatedbyanarrowspaceandcontinuouswiththeroughER.Atintervalstheinnerandouternuclearmembranesarepinchedtogetheraroundopenings(nuclearpores),whichhaveadiameterofabout90nm.Associatedwiththeporesareproteinstructurescallednuclearporecomplexes,specifictransportersthatallowcertainmacromoleculestopassbetweenthecytoplasmandtheaqueousphaseofthenucleus(thenucleoplasm[58]).Trafficintothenucleusthroughthenuclearporecomplexes[59]includesenzymesandotherproteinssynthesizedinthecytoplasmandrequiredinthenucleoplasmforDNAreplicationandrepair,transcription,andRNAprocessing.PassingoutthroughthenuclearporesaremessengerRNAprecursors,withassociatedproteins,whichwillbetranslatedonribosomesinthecytoplasm.
15.Thenucleusofaninterphase(nondividing)cellisfilledwithadiffusematerial[60]calledchromatin[61],socalledbecauseitstainedbrightlywithcertaindyes.Chromatinconsists
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ofDNAandproteinsboundtightlytogetherandisthesubstanceofthechromosomes,
whichdonotcondenseandbecomeindividuallyvisibleuntilthecellisreadytodivide.Thenucleolus[62]isaspecificregionofthenucleusinwhichtheDNAcontainsmanycopiesofthegenesencodingribosomalRNA.Toproducethelargenumberofribosomesneededbythecell,thesegenesarecontinuouslytranscribedintoRNA.ThenucleolusappearsdenseinelectronmicrographsbecauseofitshighRNAcontent.RibosomalRNAproducedinthenucleolusentersthecytoplasmthroughthenuclearpores.
16.Nucleardivision(mitosis[63])occursbeforecelldivision(cytokinesis[64]).ThedoublehelicalDNAofthechromatinisreplicated,theninthefirstphaseofmitosisthechromatinfiberscondenseintodiscretebodies,thechromosomes[65],eachconsistingoftwoidenticalchromatids[66].Thetwosisterchromatidsseparate,onemovingtoeachpoleofthecell,wheretheybecomepartofthenewlyformednucleusofeachdaughtercell.
17.Cellsofeachspecieshaveacharacteristicnumberofchromosomesofspecificsizesandshapes.Forexample,theprotist[67]Tetrahymenapyriformis[68]has5pairs;cabbagehas9,humanshave23,andthefernOphioglossumreticulatum[69]hasabout630!Thecellsthatmakeupmostofthebodyofamulticellularorganism,thesomaticcells,havetwocopiesofeachchromosomeandaresaidtobediploid[70](2n).Gametes[71](eggsandsperm,forexample),producedbymeiosis[72]andhavingonlyonecopyofeachchromosome,arehaploid(n).Duringsexualreproduction[73],twohaploidgametescombineto
generatediploidcellinwhicheachchromosomepairconsistsofamaternalandpaternalchromosome.
18.TheDNAofchromatinandchromosomesisboundtightlytoafamilyofpositivelychargedproteins,thehistones[74],whichassociatestronglywiththemanynegativelychargedphosphategroupsinDNA.AbouthalfthemassofchromatinisDNAandhalfishistones.WhenDNAreplicatespriortocelldivision,largequantitiesofhistonesarealsosynthesizedtomaintainthis1:1massratio.ThehistonesandDNAassociateincomplexescallednucleosomes[75],inwhichtheDNAstrandwindsaroundacoreofhistonemolecules.TheDNAofasinglehumanchromosomeformsaboutamillionnucleosomes;nucleosomesassociatetoformveryregularandcompactsupramolecularcomplexes.Theresultingchromatinfibers[76],about30nmindiameter,condensefurtherbyformingaseriesofloopedregions,whichclusterwithadjacentloopedregionstoformthechromosomesvisibleduringcelldivision.ThistightpackingofDNAintonucleosomesachievesaremarkablecondensationoftheDNAmolecules.TheDNAinthechromosomesofasinglediploidhumancellwouldhaveacombinedlengthofabout2miffullyextendedasaDNAdoublehelix,butthecombinedlengthoftheall46chromosomesisonlyabout200μm.
MitochondriaArethePowerPlantsofAerobicEukaryoticCells19.Mitochondriaareveryconspicuous[77]inthecytoplasmofmosteukaryoticcellswhen
viewedbyelectronmicroscope.Thesemembraneboundedorganellesvaryinsize,but
15
typicallyhaveadiameterofabout1μm,similartothatofbacterialcells.Mitochondriaalsovarywidelyinshape,number,andlocation,dependingonthecelltypeortissuefunction.Mostplantandanimalcellscontainseveralhundredtoathousandmitochondria.Generally,cellsinmoremetabolicallyactivetissuesdevotealargerproportionoftheirvolumetomitochondria.Each mitochondrionhastwomembranes.Theoutermembraneisunwrinkledandcompletelysurroundstheorganelle.Theinnermembranehasinfoldingscalledcristae[78],whichgiveitalargesurfacearea.Enclosedbytheinnermembraneisthematrix[79],averyconcentratedaqueoussolutionofenzymesandchemicalintermediatesinvolvedinenergyyieldingmetabolism.
20.Mitochondrialenzymescatalyzetheoxidationoforganicnutrientsbymolecularoxygen(O2);someoftheseenzymesareinthematrixandsomeareembeddedintheinnermembrane.ThechemicalenergyreleasedinmitochondrialoxidationsisusedtogenerateATP,themajorenergycarryingmoleculeofcells.Inaerobiccells,mitochondriaarethe
principalproducersofATP,whichdiffusestoallpartsofthecellandprovidestheenergyforcellularwork.Unlikeothermembranousstructuressuchaslysosomes,Golgicomplexes,andthenuclearenvelope,mitochondriaareproducedonlybydivisionofpreviouslyexistingmitochondria;eachmitochondrioncontainsitsownDNA,RNA,andribosomes.MitochondrialDNAcodesforcertainproteinsspecifictothemitochondrialinnermembrane.Thisandotherevidencesupportsthetheorythatmitochondriaarethedescendantsofaerobicbacteriathatlivedendosymbiotically[80]withearlyeukaryoticcells.
ChloroplastsConvertSolarEnergyintoChemicalEnergy21.Thecytoplasmofplantscontainsplastids[81],specializedorganellessurroundedbyenvelopesconsistingoftwomembranes.Mostconspicuousoftheplastidsandcharacteristicallypresentinthephotosyntheticcellsofplantsandalgae[82]arethechloroplasts.
22.Likemitochondria,thechloroplastsmaybeconsideredpowerplants,withtheimportantdifferencethatchloroplastsusesolarenergy,whereasmitochondriausethechemicalenergyofoxidizablecompounds.PigmentmoleculesinchloroplastsabsorbtheenergyoflightanduseittomakeATPand,ultimately,toreducecarbondioxidetoformcarbohydratessuchasstarchandsucrose.Photosynthesisineukaryotesandincyanobacteria[83]producesO2asabyproductofthelightcapturingreactions;Photosyntheticplantcellscontainbothchloroplastsandmitochondria.ChloroplastsproduceATPonlyinthelight;mitochondriafunctionindependentlyoflight,oxidizingcarbohydratesgeneratedbyphotosynthesisduringdaylighthours
23.Chloroplastsaregenerallylarger(diameter5μm)thanmitochondriaandhavevariousshapes.Becausechloroplastscontainahighconcentrationofthepigmentchloro
phyll[84],cellsareusuallygreen,buttheircolordependsontherelativeamountsofotherpigmentspresent.Chlorophyllandotherpigmentmolecules,whichtogethercanabsorblightenergyovermuchofthevisiblespectrum,arelocalizedintheinternalmem
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branesofthechloroplast;thesemembranesformstacksofclosedcisternaeknownasthylakoids[85].Likemitochondria,chloroplastscontainDNA,RNA,andribosomes.
Notes
[1]extracellular[9ekstr[5seljUl[]fluid细胞外液
[2]hormone[`hR:m[Un]n.激素
[3]neurotransmitter[9nju[r[u5trAnsmit[]n.神经递质
[4]antigen[`AntidV[n]n.抗原
[5]signalreceptor信号受体
[6]receptorligand[5lig[nd`laig[nd]受
体配体
[7]intracellular[9intr[5seljul[]adj.细
胞内的
[8]ionchannel[5ai[5tFAnl]离子通道
[9]acetylcholine[[7si:t[5[ulin]n.乙酰
胆碱
[10]cascade[kAs5keid]n.小 瀑 布,人 工
瀑布,分多级进行
[11]lipoprotein[7lip[5pr[uti:n]n.脂蛋白
[12]antibody[5Anti7bRdi]n.抗体
[13]mosaic[mC5zeiik]n.镶 嵌,镶 嵌 图
案,镶嵌工艺
[14]molecularantenna[An5ten[]分 子 天
线
[15]cellulose[5seljUl[us]n.纤维素
[16]invaginate[in5vAdVinneit]v.收进鞘
中,套进内部
[17]vesicle[5vesikl]n.[解][动]囊,泡,[植]小泡
[18]endosome[5end[9s[Um]n.内吞体
[19]phagocytosis[fAg[7sait[Usis]n.噬
菌作用
[20]phagosome[5fAg[s[Um]n.吞噬体
[21]particulate[p[5tikjulit]adj.微粒的
[22]peroxisome[p[5rRksis[um]n.过 氧
化物酶体
[23]convolute[5kCnv[ljut]v.回 旋,卷
绕,盘旋adj.旋绕的
[24]subcellularcompartment[5sQb5seljul[k[n5pB:tm[nt]亚细胞隔室
[25]lumen[5lju:mi:n]n.流明(光通量单
位),[解]内腔
[26]cisternae[5sisten[]n.扁囊,池,封闭
的膜系统及其围成的腔构成网状膜结
构
[27]pancreatic[9pANkri5Atik]adj.胰腺
的
[28]insulin[5insjulin]n.胰岛素
[29]roughendoplasmicreticulum [5end[U9plAzmikri5tikjul[m]粗面内质网
[30]smoothendoplasmicreticulum光 滑 内
质网
[31]tubular[5tju:bjUl[]adj.管状的
[32]skeletalmuscle[5skelitl5mQsl]n.骨
骼肌
[33]asymmetric[Asi5metrik]adj.不对称
的
[34]sort[sC:t]v.分类,拣选
[35]cisside顺式面(面向内质网的一面)[36]transside反式面(面向质膜的一面)[37]bud出芽
[38]moiety[5mCi[ti]n.一 部 分;组 成 部
分,成分
[39]secretory granule [si5kri:t [ri5grAnju:l]n.分泌颗粒
[40]lysosome[5lais[us[um]n.溶酶体
[41]polysaccharide[pRli5sAk[raid]n.多
糖
[42]nucleicacid[5nju:kliik5Asid]n.核
酸
17
[43]recyclingcenter[5ri:5saikliN5sent[]
n.废物利用中心
[44]monosaccharide[7mCn[u5sAk[raid]
n.单糖
[45]catabolize[k[5tAb[9laiz]v.(使)异
化,(使)发生分解代谢
[46]protonpump[5pr[utRnpQmp]n.质
子泵
[47]centralvacuole[sen`tra:l5vAkju[ul]中央大液泡
[48]tonoplast[5tRn[9plB:st]n.(包 围 植
物细胞液泡的)液泡膜
[49]anthocyanin[9AnW[5sai[nin]n.花青
素
[50]osmotically[Rz5mRtikli]adv.渗 透
的,渗透性的
[51]turgorpressure[5t[:g[5preF[]n.膨
压
[52]hydrogenperoxide[5haidr[udV[np[5rCksaid]过氧化氢
[53]glyoxysome[7gli5Rks[um]n.乙醛酸
循环体
[54]freeradical[5rAdidl]自由基
[55]catalase[5kAt[leis]n.过氧化氢酶,触酶
[56] glyoxylate cycle [glai5Cksi7leit5saikl]乙醛酸循环
[57]microbody[5maikr[u9bCdi]n.微体
[58]nucleoplasm [5njU:kli[plAzm]n.核
浆
[59]nuclearporecomplex核孔复合物
[60]diffusematerial[di5fju:zm[5ti[ri[l]弥散性物质
[61]chromatin[5kr[um[tin]n.染色质
[62]nucleolus[nju:5kli:[l[s]n.核仁
[63]mitosis[mi5t[usis]n.有丝分裂,核分
裂
[64]cytokinesis[7sait[ukai5ni:sis]n.细
胞质分裂
[65]chromosome[5kr[um[s[um]n.染色
体
[66]chromatid[5kr[um[tid]n.染色单体
[67]protist[5pr[utist]n.原生生物
[68] Tetrahymena pyriformis [9tetr[5haimEn[5pirifR:mis]四膜虫
[69]Ophioglossumreticulatum 心脏叶瓶尔
小草,瓶尔小草
[70]diploid(2n)[5diplRid]n.二倍体
[71]gamete[5gAmi:t]n.配子
[72]meiosis[mai5[usis]n.减数分裂
[73]sexualreproduction[5seksju[l7ri:pr[5dQkF[n]有性繁殖
[74]histone[5hist[un]n.组蛋白
[75]nucleosome[5nju:kli[s[um]n.核 小
体
[76]chromatinfiber染色质纤维
[77]conspicuous[k[n5spikju[s]adj.显著
的,显眼的
[78]cristae[5krist[]n.嵴
[79]matrix[5meitriks]n.(线粒体)基质
[80]endosymbioticallyadv.内共生地
[81]plastid[5plAstid]n.质体
[82]algae[5AldVi:]n.藻类,海藻
[83]cyanobacteria[5sai[n[bAkti[ri[]n.蓝细菌
[84]chlorophyll[5klC:r[fil]n.叶绿素
[85]thylakoid[5Wail[9kRid]n.类囊体
UNIT02 犉犈犃犜犝犚犈犛犗犉犆犈犔犔犛犃犖犇犘犚犗犜犗犘犔犃犛犕
18
犈狊狊犪狔05 犆狅犾犾狅犻犱狊:犆犺犪狉犪犮狋犲狉犻狊狋犻犮犆狅犿狆狅狀犲狀狋狊狅犳犘狉狅狋狅狆犾犪狊犿狅犳犃犾犾犆犲犾犾狊
1.Protoplasmisuniquenotonlybecauseitconsistsofhighlycomplexandspecialmoleculesbutalsobecauseofitsphysicalnature,becauseofitshighviscosity[1],protoplasmisabitlikegelatin[2]orsometimeslikeglue[3].Thephysicalnatureofprotoplasmisdeterminedbyvastareasofinterface[4]betweensomeofthosespecialmolecules,especiallyproteins,andtheprotoplasmicsolutionsinwhichtheyaresuspended.Thereactionsoflifearecatalyzedattheseenzymeinterfaces.Soilsarealsocharacterizedbyhugeinterfacesbetweenclay[5]andtoalessextent,silt[6]andsandorhumus[7]particlesandtheirsurroundings.Technologytakesadvantageofsuchsystemsinwatersofteners,
catalyticconvertersandnumerousotherapplications.2.Crucialtothephysicalnatureofprotoplasmaremembranesandparticlestoosmalltosettleout[8]bygravitybutlargerthantheatoms,smallmolecules,andionsthatformtruesoluteparticles.Whentheselargerparticlesaresuspendedinwater,theysometimesformglue,sotheyhavebeentermedcolloids,fromtheGreekwordkola,“glue”.
3.Whydocolloidsnotsettleout?Becausetheyareconstantlybeingstruckbythesurroundingmuchsmallerwatermoleculesinrapidmotion,andtheyaresmallenoughthattherandomvelocitiesoftheimpactingwatermoleculesdonotaverageout[9].Atanygivenmomentthereisahighprobabilitythatacolloidalparticleisbombardedmorestronglyononesidethanontheoppositeside.Whencolloidalparticlesareobservedinalightmicroscopebystrongilluminationfromoneside,theyappearaspointsoflight(theTyndalleffect[10],firstnoticedbyJohnTyndall,1820~1893).Theyseemtodancearoundwithmanyrandomhopspersecond.Thelargest(brightest)particlesdancelessthanthesmaller(dimmer)particles.
4.ThisisBrownianmovement[11],discoveredbytheScottishbotanistRobertBrownin1827.Itisbeautiful,evenspectacular,confirmationofkinetictheory.Thiserratic(irregular)andcontinuousmotionkeepscolloidsfromsettling.Indeed,wemightdefineacolloidalparticleasonethatisnotatruesolute[12]butissmallenoughtoremaininsus
pensionbecauseofitsBrownianmovement.Withslightlylargerparticles,thereisamuchgreaterchancethattherandombombardmentonanysidewillapproachanaveragevaluefortheentireparticle.Inthecontestbetweenkineticbombardmentandgravity,
gravitywins,sotheparticlesettles.5.ThelargestparticlesexhibitingBrownianmovementareabout100to2,000nmindiameter,dependingonshapesanddensities.Becauselightwavesare385to776nmlong,onlythelargestcolloidalparticlescancastshadows[13].Thesmallestonesrefractlightwaves,causingtheTyndalleffect,butarenotthemselvesactuallyvisibleinalightmicroscope.Smallerparticlesaretruesolutes,butthedistinctionisnotprecise.Manyparticlesinacell,includingtheribosomesandallthesingleproteinmoleculesthatare
19
enzymes,areinthecolloidalsizerange.6.Mostcolloidalparticlespassthroughfilterpaper[14],buttheycannotpassthroughcellophane[15],ascantruesoluteparticles.Suspensionparticlesaretoolargetopassthroughfilterpaper.Althoughcolloidalparticlesaresmall,eachislargeenoughtopresentasurface(alayerofatoms)tosurroundingwatermoleculesandsoluteparticles.Becauseofthesmallsizeofcolloidalparticles,theirtotalsurfaceinagivenvolumeisrelativelyhuge.Imagineasolidcubeofmaterial1cmoneachofitsedges.Therearesixfaces,soithasasurfaceareaof6cm2.Cutitonce,youexpose2cm2 moresurfaces.Continueslicingthecubeuntilyouhavereducedeachparttoacubeof10nmlongonitsedges.Nowthetotalsurfaceareais6000000cm2(600m2).Asinglecubewiththesamesurfaceareawouldbe10mhighwithavolumeof1000m3!Colloidalparticlesareseldomcubes,buttheyareofcomparativesize.
7.Thereactionsoflifeoccuronsurfaces,anditiseasytoseehowrelativelylargesurfacescanexistinasinglecell.Itisalsoeasytoseehowhydration(matricforces[16])caninfluencethewatermilieu(backgroundorsurroundings)ofcellsandsoils.
Notes
[1]viscosity[vis5kCsiti]n.黏度,黏性
[2]gelatin[5dVel[tin]n.明胶
[3]glue[glU:]n.胶,胶水
[4]interface[5int[7feis]n.分界面
[5]clay[klei]n.黏土;泥土
[6]silt[silt]n.淤泥
[7]humus[5hju:m[s]n.腐殖土
[8]settleoutv.沉降
[9]averageoutv.达到平衡
[10]Tyndalleffect丁达尔效应
[11]Brownianmovement布朗运动
[12]truesolute[trU:5sCljU:t]真溶质
[13]castshadow投下阴影
[14]filterpaper滤纸
[15]cellophane[5sel[fein]n.玻璃纸; 璐
酚
[16]matricforce基质作用力
20
犝犖犐犜03 犅犐犗犆犎犈犕犐犛犜犚犢
犈狊狊犪狔06 犆犲犾犾狊犪狀犱犜犻狊狊狌犲狊犝狊犲犱犻狀犅犻狅犮犺犲犿犻犮犪犾犛狋狌犱犻犲狊
1.Becausealllivingcellshaveevolvedfromthesameprogenitors[1],theysharecertainfundamentalsimilarities.CarefulBiochemicalstudyofjustafewtypesofcells,howeverdifferentinbiochemicaldetailsandvariedinsuperficialappearance,shouldtherefore
yieldgeneralprinciplesapplicabletoallcellsandorganisms.Theburgeoning[2]ofbiologicalknowledgeoverthepast150yearshasrepeatedlysupportedthesepropositions[3].Certaincells,tissues,andorganismshaveprovenmoreamenable[4]toexperimentalstudiesthanothers.Knowledgeinbiochemistryisderivedprimarilyfromafewrepresentativetissuesandorganisms,suchasthebacteriumE.coli,theyeastSaccharomycescerevisae[5],photosyntheticalgaesuchaschlamydomonas[6],spinach[7]leaves,
ratliver,andtheskeletalmuscleofseveralvertebrates[8].Somebiochemicalstudiesfocusontheisolation,purification,andcharacterizationofcellularcomponents;otherresearchinvestigatesthemetabolicandgeneticpathwaysoflivingcells.
2.Anexperimenterideallybeginstheisolationofenzymesandothercellularcomponentswithplentifulandhomogeneous[9]sourceofthematerial.Thecomponentofinterestoftenrepresentsonlyaminuscule[10]fractionofthetotalmaterial,andgramsorevenkilo
gramsofstartingmaterialareneededtoobtainafewmicrogramsofthepurifiedcomponent.Ahomogeneoussourceofanenzymeornucleicacid,inwhichallthecellsaregeneticallyandbiochemicalidentical,leavesnodoubtaboutwhichcelltypeyieldedthe
purifiedcomponentandmakesitsafertoextrapolate[11]theresultsofinintrostudiestothesituationinvivo.Alargecultureofbacterialcells,allderivedbydivisionfromthesameparentandthereforegeneticallyidentical,meetstherequirementforaplentifulandhomogeneoussource.Individualtissuesfromlaboratoryanimals(ratliver,pigbrain,rabbitmuscle)areplentifulsourcesofsimilar,thoughnotidentical,cells.Someanimalandplantcellsproliferate[12]incellculture,producingpopulationsofidentical(cloned)cellsinquantitiessuitableforbiochemicalanalysis.
3.Geneticmutants[13]inwhichadefectinasinglegeneproducesadefectiveprotein[14],
whichcausesaspecificfunctionaldefectinthecellororganism,areextremelyusefulinestablishingthatacertainproteinisessentialtoaparticularcellularfunction.Becauseitistechnicallymuchsimplertoproduceanddetectmutantsinbacteriaandyeast,theseorganisms(E.coliandS.cerevisae,forexample)havebeenfavoriteexperimentaltar
21
getsforbiochemicalgeneticists[15].Oncethegeneforaproteinhasbeenisolated,itcanoftenbeinsertedintoabacterialoryeastcell,whichthenactsasabiologicalfactory[16],
overproducing[17]theprotein.Withgeneticengineering[18]techniques,experimenterscanintroducespecificmutationsintosuchgenesanddeterminetheireffectsonproteinstructureandfunction.
4.Anorganismthatiseasytocultureinthelaboratory,andhasashortgenerationtime[19],offerssignificantadvantagestotheresearchbiochemist.Anorganismthatrequiresonlyafewsimpleprecursormoleculesinitsgrowthmediumcanbeculturedinthepresenceofaradioisotopicallylabeled[20]precursor,andthemetabolicfateofthatprecursorcanthenbeconvenientlytracedbyfollowingtheincorporationoftheradioactiveatomsintoitsmetabolicproducts.Theshortgenerationtimeofmicroorganisms(minutesorhours)allowstheinvestigatortofollowalabeledprecursororageneticdefectthroughmanygenerationsinafewdays.Inorganismswithgenerationtimesofmonthsoryears,thisisvirtuallyimpossible.
5.Somehighlyspecializedtissuesofmulticellularorganismsareremarkablyenrichedinsomeparticularcomponentrelatedtotheirspecializedfunction.Forstudiesonsuchspecificcomponentsorfunctions,biochemistscommonlychoosethespecializedtissuefortheirexperimentalsystems.Forexample,vertebrateskeletalmuscleisarichsourceofactin[21]andmyosin[22];pancreaticsecretorycellscontainhighconcentrationsofroughendoplasmicreticulum;spermcellsarerichinDNA;livercontainshighconcentrationsofmanyenzymesofbiosyntheticpathways;andspinachleavescontainlargenumbersofchloroplasts.
6.Sometimes,itissimplicityofstructurethatmakesaparticularcellororganismattractiveasanexperimentalsystem.Forstudiesonplasmamembranestructureandfunction,thematureredbloodcellhasbeenafavorite,becauseithasnointernalmembranes[23]tocomplicatepurificationoftheplasmamembrane.Somebacterialviruses(bacteriophages[24])havefewgenes.TheirDNA moleculesarethereforesmallerandmuchsimplerthanthoseofhumansormaizeplants.IthasprovedeasiertostudyDNAreplicationwiththesevirusesthanwitheukaryoticchromosomesbecausewhenavirusinfectsabacterialcell,thereisasynchronousburst[25]ofDNAsynthesis,oftenaccompaniedbyincreasedlevelsoftheenzymesofDNAreplication.
Notes
[1]progenitor[pr[5dVenit[]n.祖先
[2]burgeon[5b…dV[n]v.萌发
[3]proposition[9prRp[5ziF[n]n.主张,建议,陈述,命题
[4]amenable[[5mi:n[bl]adj.经得起检
验的;可 按 照……控 制[处 理,测 验]的
[5]Saccharomycescerevisaen.酵母
[6]chlamydomonas[9klAmid[5m[un[s]
n.衣藻
UNIT03 犅犐犗犆犎犈犕犐犛犜犚犢
22
[7]spinach[5spinidV5spinitF]n.菠菜
[8]vertebrate[5v[:tibrit]n.脊椎动物
[9]homogeneous[9hRm[u5dVi:nj[s]
adj.同质的
[10]minuscule[mi5nQskju:l]adj.极小的
[11]extrapolate[eks5trAp[leit]v.外 推,推断
[12]proliferate[pr[u5lif[reit]v.增 生 扩
散
[13]mutant[5mju:t[nt]n.突变体
[14]defective[di5fektiv]protein缺陷蛋白
[15]geneticist[dVi5netisist]n.遗传学家
[16]biologicalfactory生物工厂
[17]overproduce[5[uv[pr[5dju:s]v.超
量生产
[18] genetic engineering [dVi5netik7endVi5ni[riN]遗传工程
[19]generationtime世代
[20]radioisotopicallylabeled[5reidi[u7ais[U5tCpikli5leibld]放 射 性 同 位 素 标
记的
[21]actin[5Aktin]n.肌动蛋白
[22]myosin[5mai[sin]n.肌球蛋白
[23]internalmembrane内膜
[24]bacteriophage[bAk5ti[ri[feidV]n.噬菌体
[25]synchronousburst[5siNkr[n[sb[:
st]同步突发
犈狊狊犪狔07 犜犺犲αHelix[1]IsaCommonProteinSecondaryStructure[2]
1.PaulingandCoreywereawareoftheimportanceofhydrogenbondsinorienting[3]polarchemicalgroup ssuchasthe C O and N H groupsofthepeptidebond.TheyalsohadtheexperimentalresultsofWilliamAstbury,whointhe1930shadconductedpioneering[4]Xraystudiesofproteins.Astburydemonstratedthattheproteinthatmakesuphairandporcupinequills[5](thefibrousproteinαkeratin[6])hasaregularstructurethatrepeatsevery5.15to5.2.[Theangstrom[7], (namedafterthephysicistAndersJ.ngstrm),isequalto0.1nm.AlthoughnotanSIunit[8],itisuseduniversallybystructuralbiologiststodescribeatomicdistances.]Withthisinformationandtheirdataonthepeptidebond[9],andwiththehelpofpreciselyconstructedmodels,PaulingandCoreysetouttodeterminethelikelyconformations[10]ofproteinmolecules.
2.Thesimplestarrangementthepolypeptidechain[11]couldassume[12]withitsrigid[13]
peptidebonds(butothersinglebondsfreetorotate)isahelicalstructure,whichPaulingandCoreycalledtheαhelix.Inthisstructurethepolypeptidebackboneistightlywound[14]aroundanimaginaryaxisdrawnlongitudinally[15]throughthemiddleofthehelix,andtheRgroupsoftheaminoacidresidues[16]protrude[17]outwardfromthehelicalbackbone.Therepeatingunit[18]isasingleturnofthehelix,whichextendsabout5.4alongthelongaxis,slightlygreaterthantheperiodicity[19]AstburyobservedonXrayanalysisofhairkeratin.Theaminoacidresiduesinαhelixhaveconformationswithψ=-45°to-50°andφ=-60°,andeachhelicalturnincludes3.6aminoacidresidues.Thehelicaltwistofαhelixfoundinallproteinsisrighthanded.Theαhelix
23
provedtobethepredominant[20]structureinαkeratins.Moregenerally,aboutonefourthofallaminoacidresiduesinpolypeptidesarefoundinαhelices,theexactfractionvaryinggreatlyfromoneproteintothenext.Whydoestheαhelixformmorereadilythanmanyotherpossibleconformations?Theansweris,inpart,thatanαhelixmakesoptimaluseofinternalhydrogenbonds.Thestructureisstabilizedbyahydrogenbondbetweenthehydrogenatomattachedtotheelectronegative[21]nitrogenatomofthepeptidelinkageandtheelectronegativecarbonyloxygenatomofthefourthaminoacidontheaminoterminalsideofthatpeptidebond.Withinαhelix,everypeptidebond(exceptthoseclosetoeachendofthehelix)participatesinsuchhydrogenbonding.Eachsuccessiveturnoftheαhelixisheldtoadjacentturnsbythreetofourhydrogenbonds.Allthehydrogenbondscombinedgivetheentirehelicalstructureconsiderablestability.
3.Furthermodelbuildingexperiments[22]haveshownthatαhelixcanforminpolypeptidesconsistingofeitherLorDaminoacids.However,allresiduesmustbeofonestereoisomeric[23]series;aDaminoacidwilldisruptaregularstructureconsistingofLaminoacids,andviceversa.NaturallyoccurringLaminoacidscanformeitherrightorlefthandedαhelices,butextendedlefthandedheliceshavenotbeenobservedinproteins.
AminoAcidSequenceAffectsαHelixStability4.Notallpolypeptidescanformastableαhelix.Interactionsbetweenaminoacidsidechainscanstabilizeordestabilize[24]thisstructure.Forexample,ifapolypeptidechainhasalongblockof[25]glutamate(Glu)[26]residues,thissegmentofthechainwillnotformαhelixatpH7.0.ThenegativelychargedcarboxylgroupsofadjacentGluresiduesrepeleachothersostronglythattheyovercomethestabilizinginfluenceofhydrogenbondsontheαhelix.Forthesamereason,iftherearemanyadjacentlysine(Lys)[27]and/orarginine(Arg)[28]residues,whichhavepositivelychargedRgroupsat
pH7.0,theywillalsorepeleachotherandpreventformationoftheαhelix.Thebulkandshapeofasparagine(Asn)[29],serine(Ser)[30],threonine(Thr)[31],andcysteine(Cys)[32]residuescanalsodestabilizeanαhelixiftheyareclosetogetherinthechain.
5.Thetwistofαhelixensuresthatcriticalinteractionsoccurbetweenaminoacidsidechainandthesidechainthree(andsometimesfour)residuesawayoneithersideofit.Positivelychargedaminoacidsareoftenfoundthreeresiduesawayfromnegativelychargedaminoacids,eliminatingtheformationofanionpair.Twoaromaticaminoacid[33]residuesareoftensimilarlyspaced,avoidingahydrophobicinteraction.Aconstraintontheformationofαhelixisthepresenceofproline (Pro)[34]orglycine(Gly)[35]residues.Inproline,thenitrogenatomispartofarigidringandrotationa
boutthe N Ca bondisnotpossible.Thus,aProresidueintroducesadestabilizingkink[36]inαhelix.Inaddition,thenitrogenatomofProresidueinpeptidelinkagehasnosubstituenthydrogentoparticipateinhydrogenbondswithotherresidues.Forthesereasons,prolineisonlyrarelyfoundwithinαhelix.Glycineoccursinfrequentlyinαhelicesforadifferentreason:ithasmoreconformationalflexibilitythantheotheramino
UNIT03 犅犐犗犆犎犈犕犐犛犜犚犢
24
acidresidues.Polymersofglycinetendtotakeupcoiledstructurequitedifferentfromαhelix.Afinalfactoraffectingthestabilityofαhelixinapolypeptideistheidentityoftheaminoacidresiduesneartheendsoftheαhelicalsegment.Asmallelectricdipole[37]
existsineachpeptidebond.Thesedipolesareconnectedthroughthehydrogenbondsofthehelix,resultinginanetdipoleextendingdownthehelixthatincreaseswithhelixlength.Thefouraminoacidresiduesateachendofthehelixdonotparticipatefullyinthehelixhydrogenbonds.Thepartialpositiveandnegativechargesofthehelixdipoleactuallyresideonthepeptideaminoandcarbonylgroupsneartheaminoterminalandthecarboxylterminalendsofthehelix,respectively.Forthisreason,negativelychargedaminoacidsareoftenfoundneartheaminoterminusofthehelicalsegment,
wheretheyhavestabilizinginteractionwiththepositivechargeofthehelixdipole;apotivelychargedaminoacidattheaminoterminalendisdestabilizing.Theoppositeistrueatthecarboxylterminalendofthehelicalsegment.Thusfivedifferentkindsofconstraintsaffectthestabilityofαhelix:
(1)Theelectrostaticrepulsion(orattraction)betweensuccessiveaminoacidresidueswithchargedRgroups.
(2)Thebulkinessofadjacentgroups.(3)Theinteractionsbetweenaminoacidsidechainsspacedthree(orfour)residuesapart(4)TheoccurrenceofProandGlyresidues.(5)Theinteractionbetweenaminoacidresiduesattheendsofthehelixsegmentandtheelectricdipoleinherenttotheahelix.
Notes
[1]αhelix[5hi:liks]α螺旋
[2]secondarystructure二级结构
[3]orient[5R:ri[nt]v.定向
[4]pioneer[9pai[5ni[]v.开 路,创 办;打
开(新领域)或准备(途径)[5]porcupinequill[5pR:kjupainkwil]n.(豪猪、刺猬的)刚毛
[6]αkeratin[5ker[tin]n.α角蛋白
[7]angstrom[5ANstr[m]n.()埃(长
度单位)[8]SIunit:SystèmeInternationalUnit
国际(单位)制[9]peptidebond[5peptaidbRnd]n.肽键
[10]conformation[7kRnfR:5meiF[n]n.构象
[11]polypeptidechain[9pRli5peptaidtFein]
n.多肽链
[12]assume[[5sju:m]vt.采取,呈现
[13]rigid[5ridVid]adj.刚性的
[14]wind[waind]v.绕,缠,上 发 条,旋
紧
[15]longitudinally [lRndVi5tju:din[li]
adj.经度的,纵向的
[16]residue[5rezidju:]n.残基
[17]protrude[pr[5tru:d]v.伸出
[18]repeatingunit重复单位
[19]periodicity[9pi[ri[5disit]n.周期性
[20]predominant[pri5dRmin[nt]adj.卓
越的,支配的,主要的,突出的,有影
响的
25
[21]electronegative [i9lektr[u5neg[tiv]
adj.电负性的
[22]modelbuildingexperiment建模实验
[23]stereoisomeric[7sti[ri[u5ais[m[rik]
adj.立体异构体的
[24]destabilize[di:5steibilaiz]vt.去稳定
[25]alongblockof一长串的
[26]glutamate(Glu)[5glu:t[meit]n.谷
氨酸
[27]lysine(Lys)[5laisi:n]n.赖氨酸
[28]arginine(Arg)[5B:dVinin]n.精氨酸
[29]asparagine(Asn)[[s5pAr[dVi:n]n.
天冬酰胺
[30]serine(Ser)[5seri:n]n.丝氨酸
[31]threonine(Thr)[5Wri:[ni:n]n.苏
氨酸
[32]cysteine(Cys)[5sistin]n.半胱氨酸
[33]aromatic[7Ar[U5mAtik]aminoacid芳香氨基酸
[34]proline(Pro)[5pr[uli:n]n.脯氨酸
[35]glycine(Gly)[5glaisi:n]n.甘氨酸
[36]kink[kiNk]n.结节
[37]electricdipole[i5lektrik5daip[ul]n.电偶极
犈狊狊犪狔08 犇犖犃犐狊犪犇狅狌犫犾犲犎犲犾犻狓[1]
1.Toshedmorelighton[2]thestructureofDNA,RosalindFranklinandMauriceWilkinsusedthepowerfulmethodofXraydiffraction[3]toanalyzeDNAfibers.Theyshowedintheearly1950sthatDNAproducesacharacteristicXraydiffractionpattern.Fromthis
patternitwasdeducedthatDNAmoleculesarehelicalwithtwoperiodicitiesalongtheirlongaxis,aprimaryoneof3.4andasecondaryoneof34.Theproblemthenwastoformulate[4]athreedimensionalmodeloftheDNAmoleculethatcouldaccountnotonlyfortheXraydiffractiondatabutalsoforthespecificA = TandG = Cbasee
quivalences[5]discoveredbyChargaffandfortheotherchemicalpropertiesofDNA.2.In1953,WatsonandCrickpostulated[6]athreedimensionalmodelofDNAstructurethataccountedforalltheavailabledata.ItconsistsoftwohelicalDNAchainswoundaroundthesameaxistoformarighthandeddoublehelix.Thehydrophilic[7]backbonesofalternatingdeoxyribose[8]andphosphategroupsareontheoutsideofthedoublehelix,facingthesurroundingwater.Thefuranose[9]ringofeachdeoxyriboseisintheC2’endoconformation[10].Thepurine[11]andpyrimidine[12]basesofbothstrandsarestacked[13]insidethedoublehelix,withtheirhydrophobicandnearlyplanarringstructuresveryclosetogetherandperpendiculartothelongaxis.Theoffsetpairingofthetwostrandscreatesamajorgroove[14]andminorgroove[15]onthesurfaceoftheduplex.Eachnucleotidebaseofonestrandispairedinthesameplanewithabaseoftheotherstrand.WatsonandCrickfoundthatthehydrogenbondedbasepairs,GwithCandAwithT,arethosethatfitbestwithinthestructure,providingarationale[16]forChar
gaff’srulethatinanyDNA,G=CandA= T.ItisimportanttonotethatthreehydrogenbondscanformbetweenGandC,butonlytwocanformbetweenAandT.ThisisonereasonforthefindingthatseparationofpairedDNAstrandsismoredifficult
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thehighertheratioofGCtoATbasepairs.Otherpairingsofbasestend(tovaryingdegrees)todestabilizethedoublehelicalstructure.WhenWatsonandCrickconstructedtheirmodel,theyhadtodecideattheoutsetwhetherthestrandsofDNAshouldbeparallelorantiparallel[17]— whethertheir5’,3’phosphodiesterbonds[18]shouldruninthesameoroppositedirections.Antiparallelproducedthemostconvincingmodel,andlaterworkwithDNApolymerases[19]providedexperimentalevidencethatthestrandsareindeedantiparallel,afindingultimatelyconfirmedbyXrayanalysis.
3.ToaccountfortheperiodicitiesobservedintheXraydiffractionpatternsofDNAfibers,WatsonandCrickmanipulatedmolecularmodelstoarriveatastructureinwhichtheverticallystackedbasesinsidethedoublehelixwouldbe3.4apart;thesecondaryrepeatdistanceofabout34wasaccountedforbythepresenceof10basepairsineachcompleteturnofthedoublehelix.Inaqueoussolutionthestructurediffersslightlyfromthatinfibers,having10.5basepairsperhelicalturn.ThetwoantiparallelpolynucleotidechainsofdoublehelicalDNAarenotidenticalineitherbasesequenceorcomposition.Insteadtheyarecomplementary[20]toeachother.Whereveradenine[21]occursinonechain,thymine[22]isfoundintheother;similarly,whereverguanine[23]occursinonechain,cytosine[24]isfoundintheother.TheDNAdoublehelixorduplexisheldtogetherbytwoforces,asdescribedearlier:hydrogenbondingbetweencomplementarybasepairsandbasestackinginteractions[25].ThecomplementaritybetweentheDNAstrandsisattributabletothehydrogenbondingbetweenbasepairs.Thebasestackinginteractions,whicharelargelynonspecific[26]withrespecttotheidentityofthestackedbases,makethemajorcontributiontothestabilityofthedoublehelix.TheimportantfeaturesofthedoublehelicalmodelofDNAstructurearesupportedbymuchchemicalandbiologicalevidence.Moreover,themodelimmediatelysuggestedamechanismforthetransmission[27]ofgeneticinformation.TheessentialfeatureofthemodelisthecomplementarityofthetwoDNAstrands.AsWatsonandCrickwereabletosee,wellbeforeconfirmatorydatabecameavailable,thisstructurecouldlogicallybereplicatedby(1)separatingthetwostrandsand(2)synthesizingacomplementarystrandforeach.Becausenucleotidesineachnewstrandarejoinedinasequencespecifiedbythebasepairingrulesstatedabove,eachpreexisting[28]strandfunctionsasatemplatetoguidethesynthesisofonecomplementarystrand.Theseexpectationswereexperimentallyconfirmed,inaugurating[29]arevolutioninourunderstandingofbiologicalinheritance.
Notes
[1]doublehelix[5dQbl5hi:liks]双螺旋
[2]toshedmorelighton更好地说明
[3]Xraydiffraction[di5frAkF[n]X射
线衍射
[4]formulate[5fR:mjuleit]vt.把……作
成公式,用公式表示
[5]baseequivalence[i5kwiv[l[ns]碱 基
等价关系
27
[6]hydrophilic[7haidr[u5filik]adj.亲
水的
[7]deoxyribose[di:9Rksi5raib[us]n.脱
氧核糖
[8]furanose[5fju[r[7n[us]n.呋喃糖
[9]endoconformation内向构象
[10]purine[5pju[ri:n]n.嘌呤
[12]pyrimidine[5pirimidi:n]n.嘧啶
[13]stack[stAk]v.堆积
[14]majorgroove[5meidV[gru:v]n.大
沟
[15]minorgroove[5main[gru:v]n.小沟
[16]rationale[7rAF[5nB:li]n.理论基础,合逻辑的论据
[17]antiparallel[9Anti5pAr[lel]adj.反
平行的
[18]phosphodiesterbond[f[usf[dai5est[
bRnd]磷酸二酯键
[19]DNApolymerase[5pRlim[5reis]n.DNA聚合酶
[20]complementary[kRmpl[5ment[ri]n.互补的
[21]adenine[5Ad[ni:n]n.腺嘌呤
[22]thymine[5Waimi:n]n.胸腺嘧啶
[23]guanine[5gwB:ni:n]n.鸟嘌呤
[24]cytosine[5sait[si:n]n.胞嘧啶
[25]basestackinginteraction碱基堆积力
[26]nonspecific[5nRnspi5sifik]adj.非特
异的
[27]transmission[trAnz5miF[n]n.传递
[28]preexist[5pri:ig5zist]v.事先存在
[29]inaugurate[i5nR:gjureit]vt.举 行 就
职典礼,创新,开辟,举行开幕(落成、成立)典礼
犈狊狊犪狔09 犚犲犪犮狋犻狅狀狊狅犳狋犺犲犆犻狋狉犻犮犃犮犻犱犆狔犮犾犲[1]
1.Aswehaveknownthat,theendproductofglycolysis[2],pyruvate[3],isfurtheroxidizedtoyieldtheacetylgroup[4]ofacetylcoenzymeA,withlossofitscarboxylgroupasCO2andreleaseofonemoleculeofNADH[5];Thisoxidativedecarboxylation[6]reac
tioniscatalyzedbypyruvatedehydrogenasecomplex[7],aenzymecomplexexistinginmitochondrialmatrix[8],consistingofthreeenzymes — pyruvatedehydrogenase[9]
(E1),dihydrolipoyltransacetylase[10](E2)anddihydrolipoyldehydrogenase[11](E3),
andfivecoenzymesorprostheticgroups[12]—thiaminepyrophosphate[13](TPP),flavinadeninedinucleotide[14](FAD),coenzymeA (CoA),nicotinamideadeninedinucleotide(NAD),andlipoate[15].TheacetylgroupisthenoxidizedcompletelytoCO2bythecitricacidcycle(alsoknownasKrebscycleortricarboxylicacidcycle),thefirstcyclic
pathway[16]wehaveencountered.Tobeginaturnofthecycle,acetylCoAdonatesitsacetylgrouptothefourcarboncompoundoxaloacetate[17]toformthesixcarboncitrate[18],catalyzedbycitratesynthase[19].Citrateisthencatalyzedbycisaconitase[20]toformisocitrate[21],alsoasixcarbonmolecule,whichisdehydrogenated[22]byisocitratedehydrogenase[23]withlossofonemoleculeofCO2andreleaseofonemoleculeof
NADHtoyieldthefivecarboncompoundαketoglutarate[24].αketoglutarateundergoeslossofCO2withthecatalysisofαketoglutaratedehydrogenasecomplexaverysimilarcomplextopyruvatedehydrogenasecomplexandultimatelyyieldsthefourcarboncom
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poundsuccinylCoA[25]andasecondmoleculeofCO2andanothermoleculeofNADH.SuccinylCoAisthenconvertedtosuccinate[26]bysuccinylCoAsynthetase[27]orthiokinase[28],yieldingamoleculeofGTPbysubstratelevelphosphorylation[29].Succinateisthenoxidizedbysuccinatedehydrogenasetofumarate[30]andreleaseonemoleculeofFADH2.Fumarateishydratedtomalate[31]byfumarase[32].Andfinallymalateisdehydrogenatedby malatedehydrogenasetoform oxaloacetate (andone moleculeofNADH),withwhichthecyclebegan;oxaloacetateisthenreadytoreactwithanothermoleculeofacetylCoA.Ineachturnofthecycle,oneacetylgroup(twocarbons)entersasacetylCoAandtwomoleculesofCO2leave,andonemoleculeofoxaloacetateisusedtoformcitrate,butafteraseriesofreactions,theoxaloacetateisregenerated[33].Nonetremovalofoxaloacetateoccurs;onemoleculeofoxaloacetatecantheoreticallybringaboutoxidationofaninfinite[34]numberofacetylgroups,andinfact,oxaloacetateispresentincellsinverylowconcentrations.Fouroftheeightstepsinthisprocessareoxidations,inwhichtheenergyofoxidationisveryefficientlyconservedintheformofthereducedcoenzymesNADHandFADH2[35].
2.Althoughthecitricacidcycleiscentraltoenergyyieldingmetabolism,itsroleisnotlimitedtoenergyconservation.Fourandfivecarbonintermediatesofthecycleserveasprecursors[36]forawidevarietyofproducts.Toreplaceintermediatesremovedforthispurpose,cellsemployanaplerotic(replenishing)reactions[37]toreplenishitsintermediatesespeciallyoxaloacetate.
3.EugeneKennedyandAlbertLehningershowedin1948thatineukaryotestheentiresetofreactionsofthecitricacidcycletakesplaceinmitochondria.Isolatedmitochondriawerefoundtocontainnotonlyalltheenzymesandcoenzymesrequiredforthecitricacidcycle,butalsoalltheenzymesandproteinsnecessaryforthelaststageofrespiration[38]electrontransferandATPsynthesisbyoxidativephosphorylation[39].MitochondriaalsocontaintheenzymesfortheoxidationoffattyacidsandsomeaminoacidstoacetylCoA,andtheoxidativedegradationofotheraminoacidstoαketoglutarate,succinylCoA,oroxaloacetate.
4.Thusinnonphotosyntheticeukaryotes,mitochondrionisthesiteofmostenergyyieldingoxidativereactionsandofthecoupledsynthesisofATP.InphotosyntheticeukaryotesmitochondriaarethemajorsiteofATPproductioninthedark,butindaylightphotophosphorylation[40]inchloroplasts,producemostoftheorganism’sATP.Inmostprokaryotes,theenzymesofthecitricacidcycleareinthecytosol,andtheplasmamembraneplaysarolesimilartothatoftheinnermitochondrialmembraneinATPsynthesis.
Notes
[1]citricacidcycle[5sitrik5Asid5saikl] 柠檬酸循环
29
[2]glycolysis[^lai5kRlisis]糖酵解
[3]pyruvate[pai5ru:veit]丙酮酸
[4]acetylgroup乙酰基
[5]NADH:Reducednicotinamideadeninediphosphate还原性辅酶Ⅰ,还原型烟
(尼克)酰胺腺嘌呤二核苷酸
[6]oxidativedecarboxylation[5Rksideitiv7dikB:7bRks[5leiF[n]n.氧化脱羧
[7] pyruvate dehydrogenase complex[pai5ru:veitdi:5haidr[dV [7neis5kRmpleks]丙 酮 酸 脱 氢 酶 复 合 体
(系)[8]mitochondrialmatrix[7mait[5kCndri[5meitriks]线粒体基质
[9]pyruvatedehydrogenase[pai5ru:veitdi:5haidr[dV[7neis]丙酮酸脱氢酶
[10 ] dihydrolipoyl transacetylase[dai5haidr [lipCil trAnz[5setileis]二 氢 硫 辛 酸 转 乙 酰
基酶
[11]dihydrolipoyldehydrogenase[dai5haidr[lipCildi:5haidr[dV[7neis]二
氢硫辛酸脱氢酶
[12]prostheticgroup[prRs5Wetikgru:p]
n.辅基
[13]thiaminepyrophosphate(TPP)[5Wai[mi:n7pair[u5fRsfeit]n.焦磷
酸硫胺素
[14]flavinadeninedinucleotide(FAD)[5fleivin5Ad[ni:ndai5nju:kl[7taid]黄素
腺嘌呤二核苷酸
[15]lipoate[5li:p[ueit]n.硫辛酸
[16]cyclicpathwayn.循环途径
[17]oxaloacetate[9Rks[l[u5Asiteit]n.草
酰乙酸
[18]citrate[5sitrit]n.柠檬酸
[19]citratesynthase[5sitrit5sinWeis]n.柠檬酸合酶
[20]cisaconitase[sis[5kCniteis]n.顺乌
头酸酶
[21]isocitrate[ais[u5sitrit]n.异柠檬酸
[22]dehydrogenate[di:`haidr[neit]vt.脱
氢
[23]isocitratedehydrogenase[ais[u5sitritdi:
5haidr[dV[7neis]]异柠檬酸脱
氢酶
[24]αketoglutarate[7ki:t[U5glu:tt[reit]
n.α酮戊二酸
[25]succinylCoA[5sQksinilkRnei]n.琥
珀酰辅酶A[26]succinate[5sQksi9neit]n.琥珀酸
[27]succinylCoA synthetase [5sQksinilkRnei5sinWeteis]n.琥珀酰辅
酶A合成酶
[28]thiokinase[7Wai[u5kineis]n.硫激酶
[29 ] substratelevel phosphorylation[5sQbstreitlel5fRsfRrileiF[n]n.底 物
水平磷酸化
[30]fumarate[5fju:m[reit]n.延胡索酸
[31]malate[5mAleit]n.苹果酸
[32]fumarase[5fju:m[reis]n.延胡索酸酶
[33]regenerate[ri5dVen[reit]v.再生
[34]infinite[5infinit]adj.无数的
[35]FADH2:Reducedflavinadeninediphosphonucleotide还 原 型 的 黄 素 腺
嘌呤二核苷酸
[36]precursor[pri5k[:s[]n.前体
[37]anaplerotic[[n[p5ler[utik]reaction回补反应
[38]respiration[7respi55reiF[n]n.呼 吸
作用
[39]oxidativephosphorylation氧化磷酸化
[40]photophosphorylation [7f[ut[ufRsf[reiF[n]光合磷酸化
UNIT03 犅犐犗犆犎犈犕犐犛犜犚犢
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犈狊狊犪狔10 犅犾狅狅犱犛狌犫狊狋犻狋狌狋犲[1]
1.Theideaofusingabloodsubstituteinsteadofhumanbloodfortransfusing[2]patientsisnotnew.Inthe17thcentury,SirChristopherWrensuggestedthatale[3],wine,andevenopium[4]couldbeusedassubstitutesforhumanblood.Itwasnotuntil1901thatthemodernageofbloodtransfusionbeganwiththediscoveryofhumanbloodgroup[5]
antigens[6]byKarlLandsteiner.Hecategorized[7]humanbloodintoA,B,andC(laterrenamedO)groups,andayearlatertheABgroupwasaddedtothelist.Thesestudieswerecriticaltounderstandingwhybloodtransfusionshadfailedthusfar.Ottenbergin1913wasthefirsttoapplybloodgroupserology[8]totransfusionpractice.EvenwithOttenberg’sdescriptionofbloodcompatibilitytesting[9],bloodtransfusionswereseverelylimitedbecauseofalackofsuitableanticoagulants[10]andstoragemethods.TheFirstandSecondWorldWarsprecipitated[11]progressonthesetwofronts,atlastallowingbloodtransfusiontobecomeastandardpartofmedicaltreatment.
2.Oneoftheprincipaltasksofbloodistotransportoxygenthroughoutthebodyandthentoreleasetheoxygentotissues,pickingupcarbondioxideinitsstead.Allofthisisaccomplishedbyhemoglobin[12],theoxygencarryingproteincontainedwithinredbloodcells(erythrocytes[13]).Theothercellularconstituentsofbloodarewhitecells,whichareimportantfortheimmuneresponse[14],andcellularfragmentscalledplatelets[15]
thatarecrucialforbloodclottingandwoundhealing.3.Althoughtransfusionofdonorbloodisaroutineandsafeprocedure,thereareseveralreasonsfordevelopingbloodsubstitutes.Humanredbloodcellshaveexacting[16]storagerequirementsdesignedtoprolongclinicaleffectivenessandtoreducetheriskofbacterialcontamination.Thissubstantiallylimitstheavailabilityofbloodatdisastersitesoronthebattlefield.Bloodsubstituteswithlessstringent[17]storagerequirementswouldbevaluableinthesesituations.Inaddition,bloodsubstitutesaremoreamenabletosterilizationtoremoveinfectiouspathogens[18],andtheydonotrequirecrossmatching[19]becausetheydonotharbor[20]bloodgroupantigens.Donorbloodshortagesmakebloodsubstitutesattractivefortheshorttermreplacementoferythrocytesduringsurgery.Inthe1980s,therealizationthatthehumanimmunodeficiencyvirus(HIV)[21]
couldbetransmittedthroughbloodtransfusionprovidedrenewedimpetus[22]forthedevelopmentof“diseasefree”bloodsubstitutes.Beforethedevelopmentofaspecifictestfor HIV,therisk oftransfusionassociatedacquiredimmunodeficiencysyndrome(AIDS[23]wasabout38per100,000transfusedpatients).
4.Researchersinterestedindevelopingbloodsubstitutes(dubbed[24]artificialblood[25])
havepredominantlyconcentratedonmimickingtheoxygencarryingcapacityofhemo
globin.However,inadditiontobeingabletotransportoxygen,anidealbloodsubstitutewouldalso(i)requirenocrossmatchingorcompatibilitytesting,(ii)besuitable
31
forlongtermstorage(preferablyatroomtemperature),(iii)beabletosurviveinthecirculationforseveralweeks(theintravascular“dwell”time[26])beforebeingclearedbythekidney,(iv)befreeofsideeffects,(v)befreeofpathogens,and(vi)notonlytransportbutalsoeffectivelydeliveroxygentotissues.Therearetwotypesofbloodsubstitutecurrentlyunderdevelopment:thosederivedfromhemoglobin,calledhemo
globinbasedoxygencarriers(HBOCs)[27],andthosethatuseperfluorocarbonemulsions[28].
5.Thehemoglobininadulterythrocytesisatetramer[29]oftwoαandtwoβpolypeptidechains,eachofwhichisboundtoanironcontainingheme[30]group.Eachhemegroupbindsoneoxygenmolecule.Thisoxygenhemebondresultsinaconformational(shape)
changeinthehemoglobinmolecule,whichinturnprogressivelyincreasestheaffinity[31]
ofhemoglobinforadditionaloxygenmolecules.Thus,asmallchangeinoxygenpartial
pressure[32]resultsinalargechangeintheamountofoxygenboundorreleasedbyhemoglobin.Anumberofadditionalfactors,suchastemperatureandpH,canaltertheoxygenhemoglobindissociationcurve.Similarly,2,3diphosphoglycerate (2,3DPG)[33],aproductoftheredbloodcellglycolyticpathwayandpresentinnormalhumanerythrocytes,alsodirectlyaffectsthebindingofoxygentohemoglobin.Astheconcentrationof2,3DPGrises,theoxygenhemoglobindissociationcurve“shiftstotheright,”therebyallowingthereleaseofoxygentotissuesathigherthannormaloxygen
partialpressures.6.Acellfreesolutionofhemoglobincanbeusedasabloodsubstitutebecausehemoglobinmaintainsitsabilitytotransportoxygenoutsideoftheredbloodcell.OneadvantageofHBOCsisthatcompatibilitytestingisnotrequired.Incontrast,transfusionofdonorbloodrequirescarefulcrossmatchingtoavoidtheconsequencesofahemolytic[34]transfusionreactionintherecipient,thecauseofasmallbutsignificanttransfusionassociatedmorbidity[35]andmortality[36].Anotheradvantageofcellfreehemoglobinisthatitcanbesterilizedbyultrafiltration[37]andlowheattoinactivate[38]infectiousagents,astrategythatisnotpossiblewithredbloodcells.
7.Earlyattemptstodevelopbloodsubstitutesinthe1970sconcentratedoncellfreesolutionsofhumanhemoglobin.ButproblemswiththeseHBOCsincludedunacceptablyshortsurvivaltimesinthecirculation,anabnormallyhighoxygenaffinity,andclinicalsideeffectssuchasmalaise[39],abdominalpain[40],hemoglobinuria[41],andrenaltoxicity[42].IfHBOCsaretobecomeclinicallyeffectivebloodsubstitutes,twoprincipalchallengesmustbeovercome:theirshortintravasculardwelltimes,andtheirreducedabilitytooxygenatetissuesrelativetonormalhemoglobin.
8.Thefirstchallengeistopreventtherapidbreakdownandeliminationbythekidneyofhemoglobinmoleculesthatarenolongerwithintheprotectiveenvironmentoftheredbloodcell.Intracellularhemoglobinhasthesamelifespanastheerythrocyte,about120days,butinsolutionthehemoglobintetramerreadilydissociatesintomonomersanddimmers[43]thatarequicklyeliminatedbythekidneys.Thedissociationofoxygen
UNIT03 犅犐犗犆犎犈犕犐犛犜犚犢
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fromintracellularhemoglobinismodifiedby2,3DPG,resultinginanormalP50value(theoxygenpartialpressureatwhichhemoglobinis50%saturated)ofabout27mmHgforhumanblood.Inhemoglobinsolutions,thelackof2,3DPGcausesa“leftshift”intheoxygendissociationcurve,thatis,anincreaseintheaffinityofhemoglobinforoxy
gen.AlthoughthisincreasedaffinitydoesnotlimittheabilityofHBOCstotransportoxygen,itdoesseriouslylimittheirabilityto“unload”ordeliveroxygentotissues.
9.Thesetwochallengeshavebeenaddressed[44]bychemicallymodifyingcellfreehemoglobin.InthefirstclassofmodifiedHBOCs,specificchemicalcrosslinksareestablishedbetweenhemoglobinpolypeptidechainstopreventthedissociationofthehemoglobintetramer,thusretardingrenalelimination.Treatmentwith3,5dibromosalicylfumarate[45]resultsinastrongcovalentbondthatmaintainstheintegrityofthehemoglobintetramer.Thisresultsinaprolongedintravasculardwelltimeofupto12hours;bycontrast,untreatedcellfreehemoglobiniseliminatedbythekidneyinlessthan6hours.Alternatively,hemoglobincanbetreated withbifunctionalcrosslinkinga
gents[46],suchasraffinose[47]orglutaraldehyde[48],thattargetspecificaminogroupsandpolymerizethehemoglobinmolecule.Thesereagentsproducepolyhemoglobin[49],
composedoffourorfivehemoglobinmolecules,whichvariesinmolecularsizeandconfiguration[50]andhasintravasculardwelltimesofupto24hours.Finally,hemoglobincanbeconjugatedtoavarietyoflargermoleculessuchasdextran[51],polyethyleneglycol[52],orpolyoxyethylene[53],retardingtherateatwhichitisclearedfromthecirculation.Inthisinstance,theintravasculardwelltimecanbeextendedto48hours.NewHBOCsunderdevelopmentincludepolyhemoglobinlinkedtoantioxidant[54]enzymessuchassuperoxidedismutase[55]andcatalaseinanefforttominimizeischemiareperfusioninjury[56].Inaddition,somegroupsaretryingtopackagehumanhemoglobininartificialredbloodcellsmadefrombiodegradablepolymernanocapsules[57]orlipidvesicles[58].
10.Thereareatleastthreemodifiedhemoglobinproductscurrentlyinadvancedclinicaltrials.NorthfieldLaboratorieshasdevelopedPolyheme,apolymerizedhumanhemoglobin
product.Biopurehaspreparedpolymerizedhemoglobinfrombovine[59]redbloodcells(Hemopure),whichhasreceivedapprovalforuseasabloodsubstituteintheRepublicofSouthAfricaandisnowawaitingFDAreviewofaphaseIIIclinicaltrialintheUnitedStates.Finally,HemosolhasdevelopedHemolink,apartiallypolymerizedhumanhemoglobinproductthatisalsounderFDA[60]review.
11.ThereareseveralproblemswithHBOCsthatmustbeovercome.Thefirstisthesourceofthehemoglobinusedinthebloodsubstitute.Anobviouscandidateishumanhemo
globinderivedfromoutdateddonorblood(redbloodcellsthathaveexceededtheap
provedstorageperiod),butthelimitedsupplyofhumanbloodhascompoundeddifficultiesindevelopingahumanderived HBOC.A morereadilyavailable(andcheaper)
sourceofhemoglobinisbovineblood.Bovinehemoglobindoesnothave2,3DPG,resultinginaP50ofabout30mmHgbothinsideandoutsidetheredbloodcell(similarto
33
thatoftheintracellularnativehumanhemoglobin).Inaddition,oncestrippedofallotherproteins,bovinehemoglobinisnotrecognizedbythehumanimmunesystemasforeign.However,onepotentialobstacletotheacceptanceofabovinederivedHBOCisthefearthatitcouldharbortheprion[61]pathogenthatcausesbovinespongiformencephalopathy[62].Geneticallyengineeringbacteriatoproducearecombinantsourceofhumanhemoglobinwouldeliminatetheconcernsaboutdiseasetransmissionassociatedwithhemoglobinderivedfromhumansoranimals.Ofcourse,theproblemwiththisapproachisthecostofscalingupoperationssufficientlytoyieldthelargevolumesofhemoglobinrequiredforroutinetransfusions。
Notes
[1]bloodsubstitute[blQd5sQbstitjuit]
n.血液替代品
[2]transfuse[trAns5fju:z]vt.输血
[3]ale[eil]n.淡色啤酒(较一般啤酒含更
多的酒精)[4]opium[5[upj[m]n.鸦片
[5]bloodgroup[blQdgru:p]n.血型
[6]antigen[5AntidV[n]n.抗原
[7]categorize[5kAtig[raiz]v.加 以 类
别,分类
[8]serology[si[5rl[dVi]n.血清学
[9]bloodcompatibility[k[m7pAti5biliti]
testing血液兼容性试验
[10]anticoagulant[5Antik[U5Agjul[nt]
n.抗凝血剂
[11]precipitate[pri5sipiteit]vt.加 速,促
使,促成
[12]hemoglobin[7hi:m[u5gl[ubin]n.血
红蛋白
[13]erythrocyte[i5riWr[usait]n.红细胞
[14]immuneresponse[i5mju:nris5pRns]
n.免疫反应
[15]platelet[5pleitlit]n.血小板
[16]exacting[ig5zAktiN]adj.苛 求 的,
严格的,吃力的,需付出极大耐心
[17]stringent[5strindV[nt]adj.严厉的,
迫切的,银根紧的
[18]pathogen[5pAW[dV[n]n.病 菌,病
原体
[19]crossmatching交叉匹配
[20]harbor[5hB:b[]vt.为……提供地方、
住房或栖息地
[21]humanimmunodeficiencyvirus(HIV)[5hju:m[n7imjun[di5fiF[nsi5vai[r[s]n.人 类 免 疫 缺 陷 病 毒(艾 滋 病 病
原)[22]impetus[5impit[s]n.推动力,促进
[23]acquiredimmunodeficiencysyndrome(Aids)[[5kwai[d7imjun[di5fiF[nsi5sindr[um]n.获 得 性 免 疫 缺 陷 综 合
症(艾滋病)[24]dub[dQb]vt.[电 影]配 音,给……起
(绰号)[25]artificialblood[7B:ti5fiF[lblQd]n.
人造血液
[26]intravascular[7intr[5vAskjul[]“dwell”time血管内停留时间
[27]hemoglobinbasedoxygencarriers(HBOCs)基于血红蛋白的氧载体
[28]perfluorocarbonemulsion[p[7flu:[r[5kB:b[ni5mQlF[n]全 氟 碳 化 合 物
乳剂
[29]tetramer[5tetr[m[]n.四聚体
[30]heme[hi:m]n.血红素
UNIT03 犅犐犗犆犎犈犕犐犛犜犚犢
34
[31]affinity[[5finiti]n.亲和力
[32]partialpressure分压
[33]2,3diphosphoglycerate(2,3DPG)[dai9fRsf[u5glis[reit]2,3二 磷 酸 甘
油酸
[34]hemolytictransfusion[hi:mR5litiktrAns5fjuV[n]reaction溶血性输血反
应
[35]morbidity[mR:5biditi]n.发病率
[36]mortality[mR:5tAliti]n.死亡率
[37]ultrafiltration[7Qltr[fil5treiF[n]n.超滤(作用)
[38]inactivate[in5Akiveit]vt.使钝化,减
除……的活性;破坏(细 菌 等 的)传 染
性
[39]malaise[mA5leiz]n.[法]不 适;小
病,精神欠爽
[40]abdominal[Ab5dRminl]pain腹痛
[41]hemoglobinuria[7hi:m[7gl[ubi5nju[ri[]n.血红蛋白尿
[42]renaltoxicity[5ri:nltRk5sisiti]n.肾
脏毒性
[43]dimer[5daim[]n.二聚体
[44]address[[5dres]vt.处理,从事,忙于
[45]3,5dibromosalicylfumarate[5daibr[um[u5sAlisil5fju:m[reit]3,5二 溴 水 杨
酰延胡索酸
[46]bifunctional[7bai5fQnkF[nl]cross-linkingagent双功能交联剂
[47]raffinose[5rAfin[us]n.棉子糖
[48]glutaraldehyde[7glu:t[5Aldi9haid]
n.戊二醛
[49]polyhemoglobin [pRli7hi:m [u5gl[ubin]n.多聚血红蛋白
[50]configuration[k[n7figju5reiF[n]n.构型
[51]dextran[5dekstrEn]n.葡聚糖
[52 ] polyethylene glycol (PEG )[7pRli5eWili:n5glaikRl]n.聚乙二醇
[53]polyoxyethylene[7pRli5[uksieWili:n]
n.聚氧乙烯
[54]antioxidant[5Anti5Cksid[nt]adj.抗
氧化的
[55]superoxidedismutase(SOD)[7sjU:p[5Rksaiddismju:teis]n.超氧物歧化
酶
[56]ischemiareperfusioninjuryn.缺血再
灌注损伤
[57]biodegradablepolymernanocapsule[nAn[u5kApsjul]n.生 物 可 降 解 的 多 聚 物
微胶囊
[58]lipidvesicle[5lipid5vesikl]n.脂质小
泡
[59]FDAn.(美 国)食 品 及 药 物 管 理 局
(FoodandDrugAdministration)[60]bovine[5b[uvain]adj.牛的,[61]prion[prai[n]n.朊病毒(感染性蛋白
质):极 微 小 的 蛋 白 质 微 粒,类 似 于 病
毒,但不含核酸,被认为是绵羊痒病和
其他的一 些 神 经 系 统 变 性 疾 病(如 疯
牛病)的传染介质。[62]bovinespongiformencephalopathy[5b
[uvain5spQndVifR:m en9sf[5lRp[Wi]n.牛绵状脑病
35
犝犖犐犜04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
犈狊狊犪狔11 犛狋狅犿犪狋犪犾犃狀犪狋狅犿狔
1.Stomata[1]comeinconsiderablevariety.Thewaxycuticle[2]onleafsurfacesrestrictsdiffusion[3],somostwatervaporandothergasesmustpassthroughtheopeningsbetweentheguardcells.Someanatomists[4]insistthatthetermstomarefersonlytothisopening,butothersapplythistermtotheentirestomatalapparatus[5],whichincludestheguardcells.Theopeningisthencalledthestomatalpore[6].Adjacenttoeachguardcellareusuallyonetoseveralothermodifiedepidermalcellscalledaccessoryorsubsidiarycells[7],thenumberandarrangementdependingontheplantfamily,althoughdifferenttypescanoccuronasingleleaf.Waterevaporatesinsidetheleaffromcellwallsofthepalisadeparenchyma[8]andspongyparenchyma[9],collectivelythemesophyll[10],
intotheintercellularspaces,whicharecontinuouswiththeoutsideairwhenthestomataareopen.Carbondioxidefollowsthereversediffusionpathintotheleaf.Manyofthecellwallsofmesophyllcellsareexposedtotheinternalleafatmosphere,althoughthisisseldomevidentforpalisadecellsindrawingsandphotomicrographsofleafcrosssections.Thisarrangementbecomesmuchmoreapparentinsectionsthroughthepalisade,
paralleltotheleafsurface,andisalsostrikinglyapparentinscanningelectronmicro
graphs.Thereismuchvariabilityintheanatomyofleaves.AspecialkindofphotosynthesiscalledC4photosynthesisisespeciallyprevalentintropicalgrassessuchasmaize.LeaveswithC4photosynthesishaveaspecialanatomycalledKranzanatomy[11](fromtheGermanwordforwreath)inwhichthelayerofcellsaroundthevascularbundles[12]
isespeciallyprominent,withalargenumberofchloroplasts.Mostplantshavebundlesheathcells[13],buttheyareeasytooverlookinspeciesthatdonothaveKranzanatomy.ItplaysaspecialroleinC4photosynthesis.
2.Stomatasometimesoccuronlyonthelowersurfacesofleavesbutoftenarefoundonbothsurfaces,oftenwithmoreonthebottoms.Waterlilypadshavestomataonlyontop,andsubmergedplantshavenoneatall.Grassesusuallyhaveaboutequalnumbersoneachside.Sometimes,asintheoleander[14]orpine,thestomataoccurinastomatalcrypt[15].Suchsunkenstomataareapparentlyanadaptationthatreducestranspiration.
3.Typicalstomataofdicots[16]consistoftwokidneyshapedguardcells[17];grassandsedgeguardcellstendtobemoreelongate(dumbbellshaped[18]).Guardcellscontainafewchloroplasts,whereastheirneighboringepidermalcellsusuallydonot(exceptin
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
36
fernsandafewaquaticangiosperms[19]).Typically,thereareno(orincomplete)plasmodesmata[20]connectingtheprotoplastsofguardcellsandaccessorycells,buttheremaybeplasmodematabetweenguardcellsandthemesophyllcellsbelow.
4.Typically,eachsquaremillimeterofleafsurfacehasabout100stomata,butthenumbercanbetentimesthat,withamaximumsofarrecordedof2,230.RecentstudiessuggestthatstomataldensitiesaresensitivetoCO2concentration,withfewerstomataperunitareaasCO2increases.Thiswasshownbybothlaboratorystudiesandbystomatacountsofagivenspeciesasafunctionofincreasingelevation(CO2partialpressuredecreasesalongwiththeothergasesintheatmospherewithincreasingelevation).Itwasalsofoundbyexaminingherbarium[21]specimens[22]thatstomataldensitieshavedecreasedby40percentoverthepasttwocenturiesasCO2intheatmospherehasincreasedfrom280toover350μmolmol
-1
Notes
[1]stomata[5st[umeit[]n.气孔 (pl.ofstoma)
[2]cuticle[5kju:tikl]n.角质层
[3]diffusion[di5fju:V[n]n.扩散
[4]anatomist[[5nAt[mist]n.解剖学家
[5]stomatalapparatus气孔器
[6]stomatalpore气孔
[7]accessoryorsubsidiarycells护卫细胞
[8]palisadeparenchyma [7pAli5seidp[5reNkim[]n.栅栏薄壁组织
[9]spongy parenchyma [5spQndVi p[5reNkim[]n.海绵薄壁组织
[10]mesophyll[5mes[fil]n.叶肉
[11]Kranzanatomy花环状结构
[12]vascularbundle[5vAskjunl[5bQndl]
n.微管束
[13]bundlesheathcell微管束鞘细胞
[14]oleander[9[uli5And[]n.夹竹桃
[15]stomatalcrypt[kript]n.气孔隐囊
[16]dicot[5daikRt]n.双子叶植物
[17]kidneyshapedguardcell肾 形 保 卫 细
胞
[18]dumbbellshaped 哑 铃 性 的(保 卫 细
胞)[19]angiosperm [5AndVi[u7sp[:m]n.被
子植物
[20]plasmodesmata[9plAzm[u5dezmeit[]
n.胞间连丝(pl.ofplasmodesma)[21]herbarium[h[:5bZ[ri[m]n.植物标本
室,腊叶集,干燥标本集
[22]specimen[5spesim[n]n.标本
犈狊狊犪狔12 犜犺犲犘犪狉犪犱狅狓狅犳犘狅狉犲狊
1.Natureoftenprovestobemorecomplexthanweexpect.Supposewecomparetheevaporationratefromabeaker[1]ofwaterandfromanidenticalbeakerthatishalfcovered,
saywithmetalstrips[2].Wewouldexpectevaporationfromthesecondbeakertobeabouthalfofthatfromthefirst.Nowlet’scoverallbutabout1percentofthesecond
37
beaker.Westilluseathinpieceoffoil[3]withsmallholesmakingupabout1percentofthetotalarea.Willwemeasureabout1percentasmuchevaporation?Notiftheholeshaveaboutthesamesizeandspacingasstomatafoundintheepidermis[4]ofaleaf.Wewillinfactmeasureabouthalfasmuchevaporationasfromtheopensurface.
2.Howcanthisbe?Whyisn’tevaporationdirectlyproportionaltosurfacearea?Itcertainlyseemsparadoxical[5]thatstomatalopeningsontheleafmakeuponlyabout1percentofthesurfacearea,whereastheleafsometimestranspires[6]halfasmuchwateraswouldevaporatefromanequivalentareaofwetfilterpaper.Weresolvethisapparentparadoxbyrealizingthatevaporationisadiffusionprocessfromwatersurfacetoatmosphere.Simplystated,diffusionisproportionaltothedrivingforceandtheconductivity[7].Inourexample,thedrivingforceisthesameforbothbeakers:thedifferenceinvaporpressure(ordensity)betweenthewatersurface(wheretheatmosphereissaturatedwithvapor)andtheatmospheresomedistanceaway(whereitmustbebelowsaturationifevaporationistooccur).
3.Thedifferentevaporationratesdependondifferentconductivitiestodiffusion.Partoftheconductivityisafunctionofthearea,andthisvalueismuchlowerabovethebeakercoveredwithporousfoil,whichiswhatweexpected.Buttheotherpartoftheconductivitydependsonthedistanceintheatmospherethroughwhichwatermoleculesmustdiffusebeforetheirconcentrationreachesthatoftheatmosphereasawhole.Theshorterthedistanceis,thehighertheconductivity.Thisdistancecanbecalledtheboundarylayer[8],anditismuchshorterabovetheporesinthefoilthanabovethefreewatersurface.Moleculesevaporatingfromthefreewaterwillbepartofarelativelydensecolumnofmoleculesextendingsomedistanceabovethesurface,whereasmoleculesdiffusingthroughaporecangoinanydirectionwithinanimaginaryhemisphere,theconcentrationdropsrapidlywithdistancefromthepore,whichistosaythattheconcentrationgradient[9]isverysteepbecausetheboundarylayerisverythin.Ofcourseifporesareclosertogetherthanthethicknessoftheirboundarylayers,thesehemispheresoverlapandmergeintoaboundarylayer.
4.Manyempiricalstudiesweremadeseveraldecadesagotodeterminetheeffectsofporesize,shape,anddistributionondiffusionrates.Stomataoftypicalplantsprovedtobenearlyoptimalformaximumgasorvapordiffusion.Thus,plantsareideallyadaptedforCO2absorptionfromtheatmospherebutalsoforlossofwaterbytranspiration.Thestomatacanclose,however,andinmostplantstheyareadaptedtoclosewhenphotosynthesisandCO2absorptionstop(forexample,indarkness).
Notes
[1]beaker[5bi:k[]n.烧杯
[2]metalstripsn.铁带,钢带
[3]foil[fRil]n.锡箔纸
[4]epidermis[7epi5d[:mis]n.表皮
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
38
[5]paradoxical[7pAr[5dRksiik[l]adj.奇
怪的
[6]transpire[trAns5pai[]v.蒸 发,蒸 腾;泄漏机密
[7]conductivity[7kRndQktiviti]n.传 导
性
[8]boundarylayer界面
[9]concentrationgradient[7kRnsen5treiF[n5greidi[nt]n.浓度梯度
犈狊狊犪狔13 犗狊犿狅狊犻狊
1.Itisaneverydayexperiencetoturnonawaterfaucet[1]orflushatoilet[2].Thusweare
perfectlyfamiliarwithwatermovementasabulkflowphenomenon[3]—ourplumbingsystems[4]seetothat!Butintheworldaroundus,vastquantitiesofwateraremoving,
usuallyinvisibly,bydiffusion.2.Ittakessomementalefforttovisualizethesemoreunfamiliaraspectsoftherealworld.Withourmind’seye(thereisnootherway)wemustseethosewatermolecules,flyingandbouncingbillionsoftimeseachsecondinthevaporstate,holdingeachotherintheliquidstatewiththeirhydrogenbonding—positivesideofonetonegativesideofanother—evenwhiletheirkinetic[5]motionscausesometoseparate.Wemustsomehow
conceptualizetheentropy[6],freeenergy,andchemicalpotentials[7]andhowthese
propertiescandrivethemoleculestodiffusedownagradient.Wemustrealizethat
pressureincreasesfreeenergiesandchemicalpotentials,whereassoluteparticlesandmatricsurfacesdecreasethem.
3.Withthesemodelsinmind,wearereadytoextendourconceptstothecellsofplants.Wearereadytodiscussosmosisandrelatedmatters.
4.Adevicethatmeasuresosmosisisanosmometer[8].Thisisusuallyalaboratorydevice,
butalivingcellmaybethoughtofasanosmoticsystem.Inbothcases,twothingsareusuallypresent:First,twoormorevolumesofsolutionsorpurewaterareisolatedfromeachotherbyamembranethatrestrictsthemovementofsoluteparticlesmorethanitrestrictsthemovementofsolventmolecules.Second,thereisusuallysomemeansofallowingpressuretobuildupinatleastoneofthevolumes.Inthelaboratoryosmometer,pressuretypicallybuilduphydrostaticallybyraisingthesolutioninthetubea
gainstgravity,butothermeanscanbeused,suchasavolumedetector(forexample,alightbeamandphotocell[9])thatcanincreasepressureinthesystem(forexample,withapiston[10])assoonasthevolumeofliquidbeginstoexpandbythefirstsmallincrement.Inthecell,therigidityoftheplantcellwallisresponsiblefortheincreasein
pressure.5.Itisimportanttoemphasizethestructuraldifferencesbetweenthecellmembraneandthecellwall.Themembraneallowswatermoleculestopassmorerapidlythansolute
particles;theprimarycellwallisusuallyhighlypermeabletoboth.Itistheplantcell
39
membranethatmakesosmosispossible,butitisthecellwallthatprovidestherigiditytoallowabuildupinpressure.Animalcellsdonothavewalls,sowhenpressuresbuildupinthem,theyoftenburst,ashappenswhenredbloodcellsareplacesinwater.Tur
gidcellsprovidemuchoftherigidityofnonwoodyplantparts.6.Consideratfirstaperfectosmometer.Insuchadevice,themembraneissemipermea
ble[11],allowingreadypassageofsolvent(water),butnopassageofsolute,andthesolutionissostronglyconfinedthatmovementofwaterintotheosmometercausesnosignificantincreaseinsolutionvolume.Anearlyperfectosmometercanbeconstructedinthelab,butacellisneverperfectosmoticsystem.
7.Restrictingthediffusionofsoluteparticlescomparedwithsolventmoleculescanresultintheestablishmentofawaterpotentialgradient[12].Ifthereispurewaterononesideofthemembraneandasolutionontheotherside(typicallyinsidethelaboratoryosmometerorthecell),thenthewaterpotentialofthesolutionwillbelowerthanthatofthepurewater.Byconvention[13],waterpotentialofpurewateratatmosphericpressureandatthesametemperatureassolutionbeingconsideredissetequaltozero,sothewaterpotentialofanaqueoussolutionatatmosphericpressurewillbesomenegativenumber(lessthanzero).Hence,watermoleculeswilldiffusefromthehigherwaterpotentialontheoutsidetothelowerwaterpotentialinthecellsolution;thatis,waterwilldiffuse“down”awaterpotentialgradientintothesolution.Theresultwillbeabuildupofpressurewithinthesystem,eitheraraiseofliquidinthetubeofthelaboratoryosmometerorofpressureuponthecellwall.Increasingpressureraisesthewater
potential,sothewaterpotentialwithintheosmoticsystemwillbegintoincreasetowardzero.
8.Thesituationisanalogoustothescaleofathermometer,butinthiscasewearedealingalmostexclusivelywithvaluesbelowzero.Addingsolutedecreasesthewaterpotentialtosomelevelbelowzero,andaddingpressureraisesthistowardzero.
9.Ifpurewaterisononesideofthemembrane,pressureontheothersidewillincreaseuntilthewaterpotentialofthesolutionisequaltozero,thatis,equaltothewaterpotentialofthepurewaterontheotherside.Whenwaterpotential(ψ)areequalonbothsides,thewaterpotentialdifference(Δψ)betweenthetwosidesofthemembraneiszero,andequilibriumhasbeenachieved(Δψ=ψ1-ψ2=0).
10.Ifononesideofthemembranethereisasolutionandontheothersideanothersolutionofdifferentconcentration,osmosiswillstilloccur.Themoreconcentratedsolutionwillhavethelower(morenegative)waterpotential,sowaterwilldiffuseintoitfromtheothersolutionuntilitspressurebuildsup,ifitisconfinedsothatthatispossible,tothe
pointatwhichitswaterpotentialequalsthatofthelessconcentratedsolution.Ifdiffusionoccursintoasolutionthatisnotconfined,itwillcontinueuntilmoreconcentratedsolutionhasbeendilutedtothepointatwhichitswaterpotentialequalsthatofthesolutionontheothersideofthemembrane.Ineithercase,bothsolutionswillhaveawater
potentialofsomenegativebutequalvalue,andequilibriumwillhavebeenreached.
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
40
11.Actually,theprocessiscompletelygeneral.Therecouldbepressureonbothsolutions,
orthesolutionoutsidetheosmometermightbemoreconcentrated(waterwouldmoveout),butwhenequilibriumisachieved,waterpotentialwillbeequalinallpartsofthesystem(ψ1=ψ2=ψi,andhence,Δψ=0).Thisisnottosaythatψ=0inallpartsofthesystem;twosolutionsinequilibriumwitheachotheracrossamembranewouldbothhavethesamewaterpotentialofsomenegativenumber.
Notes
[1]waterfaucet[5fC:sit]n.水龙头
[2]flush[flQF]atoilet冲厕所
[3]bulkflowphenomenon[fi5nCmin[n]集流现象
[4]plumbing[5plQmiN]system 排 水 管
道系统
[5]kinetic[kai5netik]adj.动力学的
[6]entropy[5entr[pi]n.熵
[7]chemicalpotential化学势
[8]osmometer[Cz5mRmit[]n.渗透计
[9]photocell[5f[ut[sel]n.光电池
[10]piston[5pist[n]n.活塞
[11]semipermeable [5semi5p[:mj[bl]
adj.半渗透性的
[12]waterpotentialgradient水势梯度
[13]convention[k[n5venF[n]n.惯例
犈狊狊犪狔14 犘狉犻狀犮犻狆犾犲狊狅犳犘犺狅狋狅狊狔狀狋犺犲狋犻犮犈狀犲狉犵狔犜狉犪狀狊犳狅狉犿犪狋犻狅狀
1.Theenergythatdrivesphotosynthesisoriginatesinthecenterofthesun,wheremassisconvertedtoheatbythefusionofhydrogen.Overtime,theheatenergyreachesthesun’ssurface,wheresomeofitisconvertedtolightbyblackbody[1]radiationthatrea
chestheearth.Asmallfractionofthevisiblelightincidenton[2]theearthisabsorbedbyplants.Throughaseriesofenergytransducingreactions,photosyntheticorganismsareabletotransformlightenergyintochemicalfreeenergyinastableformthatcanlastforhundredsofmillionsofyears(e.g.fossilfuels).Asimplifiedscheme[3]describinghowenergyistransformedinthephotosyntheticprocessispresentedinthissection.Thefocusisonthestructuralandfunctionalfeaturesessentialfortheenergytransformingreactions.Forclarity,mechanisticandstructuraldetailsareomitted.A morehighlyresolveddescriptionofoxygenicandanoxygenic[4]photosynthesisisgivenintheremainingsections.
2.Thephotosyntheticprocessinplantsandalgaeoccursinsmallorganellesknownaschloroplaststhatarelocatedinsidecells.Themoreprimitivephotosyntheticorganisms,forexampleoxygeniccyanobacteria,prochlorophytes[5]andanoxygenicphotosyntheticbacteria,lackorganelles.Thephotosyntheticreactionsaretraditionallydividedintotwostages—the“lightreactions[6],”whichconsistofelectronandprotontransferreac
41
tionsandthe“darkreactions[7],”whichconsistofthebiosynthesisofcarbohydratesfromCO2.Thelightreactionsoccurinacomplexmembranesystem(thephotosyntheticmembrane)thatismadeupofproteincomplexes,electroncarriers,andlipidmolecules.Thephotosyntheticmembraneissurroundedbywaterandcanbethoughtofasatwodimensionalsurfacethatdefinesaclosedspace,withaninnerandouterwater
phase.Amoleculeorionmustpassthroughthephotosyntheticmembranetogofromtheinnerspacetotheouterspace.Theproteincomplexesembedded[8]inthephotosyntheticmembranehaveauniqueorientation[9]withrespecttotheinnerandouterphase.Theasymmetrical[10]arrangementoftheproteincomplexesallowssomeoftheenergyreleasedduringelectrontransporttocreateanelectrochemicalgradient[11]ofprotonsacrossthephotosyntheticmembrane.
3.Photosyntheticelectrontransportconsistsofaseriesofindividualelectrontransferstepsfromoneelectroncarriertoanother.Theelectroncarriersaremetalioncomplexesandaromaticgroups.Themetalioncomplexesandmostofthearomaticgroupsareboundwithinproteins.Mostoftheproteinsinvolvedinphotosyntheticelectrontransportarecomposedofnumerouspolypeptidechainsthatlace[12]throughthemembrane,providingascaffold[13]formetalionsandaromaticgroups.Anelectronentersaproteincomplexataspecificsite,istransferredwithintheproteinfromonecarriertoanother,andexitstheproteinatadifferentsite.Theproteincontrolsthepathwayofelectronsbetweenthecarriersbydeterminingthelocationandenvironmentofthemetalioncomplexesandaromaticgroups.Bysettingthedistancebetweenelectroncarriersandcontrollingtheelectronicenvironmentsurroundingametalioncomplexoraromaticgroup,theproteincontrolspairwiseelectrontransferreactions.Betweenproteins,electrontransferiscontrolledbydistanceandfreeenergy,andbytheprobabilitythatthetwoproteinsareinclosecontact.Proteinassociationiscontrolledbyanumberoffactors,includingthestructureofthetwoproteins,theirsurfaceelectricalandchemicalpropertiesandthe
probabilitythattheycollidewithoneanother.Notallelectroncarriersareboundto
proteins.Thereducedformsofplastoquinone[14]orubiquinone[15]andnicotinamideadeninedinucleotidephosphate(NADPH)orNADHactasmobileelectroncarriersoperatingbetweenproteincomplexes.Forelectrontransfertooccur,thesesmallmoleculesmustbindtospecialpocketsintheproteinsknownasbindingsites.Thebindingsitesarehighlyspecificandareacriticalfactorincontrollingtherateandpathwayofelectrontransfer.
4.Thelightreactionsconvertenergyintoseveralforms.Thefirststepistheconversionofaphoton[16]toanexcitedelectronicstateofanantennapigment[17]moleculelocatedintheantennasystem[18].Theantennasystemconsistsofhundredsofpigmentmolecules(mainlychlorophyllorbacteriochlorophyll[19]andcarotenoids[20])thatareanchored[21]
toproteinswithinthephotosyntheticmembraneandserveaspecializedproteincomplexknownasareactioncenter[22].Theelectronicexcitedstateistransferredovertheantennamoleculesasanexciton[23].Someexcitonsareconvertedbackintophotonsandemit
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
42
tedasfluorescence[24],someareconvertedtoheat,andsomearetrappedbyareactioncenterprotein.Excitonstrappedbyareactioncenterprovidetheenergyfortheprimaryphotochemicalreaction[25]ofphotosynthesis—thetransferofanelectronfromadonormoleculetoanacceptormolecule.Boththedonorandacceptormoleculesareattachedtothereactioncenterproteincomplex.Onceprimarychargeseparation[26]occurs,thesubsequentelectrontransferreactionsareenergetically[27]downhill.
5.Inoxygenicphotosyntheticorganisms[28],twodifferentreactioncenters,knownasphotosystem[29]IIandphotosystemI,workconcurrently[30]butinseries.InthelightphotosystemIIfeedselectronstophotosystemI.TheelectronsaretransferredfromphotosystemIItothephotosystemIbyintermediate[31]carriers.ThenetreactionisthetransferofelectronsfromawatermoleculetoNADP+,producingthereducedform,
NADPH.Inthephotosyntheticprocess,muchoftheenergyinitiallyprovidedbylightenergyisstoredasredoxfreeenergy[32](aformofchemicalfreeenergy)inNADPH,tobeusedlaterinthereductionofcarbon.Inaddition,theelectrontransferreactionsconcentrateprotonsinsidethemembranevesicleandcreateanelectricfieldacrossthephotosyntheticmembrane.Inthisprocesstheelectrontransferreactionsconvertredoxfreeenergyintoanelectrochemicalpotentialofprotons.Theenergystoredintheprotonelectrochemicalpotentialisusedbyamembraneboundproteincomplex (ATPSynthase[33])tocovalentlyattachaphosphategrouptoadenosinediphosphate(ADP),
formingadenosinetriphosphate(ATP).ProtonspassthroughtheATPSynthaseproteincomplexthattransformselectrochemicalfreeenergyintoatypeofchemicalfreeenergyknownasphosphategrouptransferpotential[34](orahighenergyphosphatebond).TheenergystoredinATPcanbetransferredtoanothermoleculebytransferringthephosphategroup.TheneteffectofthelightreactionsistoconvertradiantenergyintoredoxfreeenergyintheformofNADPHandphosphategrouptransferenergyintheformofATP.Inthelightreactions,thetransferofasingleelectronfromwatertoNADP+involvesabout30metalionsand7aromaticgroups.Themetalionsinclude19Fe,5Mg,4Mn,and1Cu.Thearomaticsincludequinones[35],pheophytin[36],
NADPH,tyrosine[37]andaflavoprotein[38].TheNADPHandATPformedbythelightreactionsprovidetheenergyforthedarkreactionsofphotosynthesis,knownastheCalvincycle[39]orthephotosyntheticcarbonreductioncycle[40].Thereductionofatmos
phericCO2tocarbohydrateoccursintheaqueousphaseofthechloroplastandinvolvesaseriesofenzymaticreactions.ThefirststepiscatalyzedbytheproteinRubisco(Dribulose1,5bisphosphatecarboxylase/oxygenase)[41]whichattachCO2toafivecarboncompound.Thereactionproducestwomoleculesofathreecarboncompound.Subse
quentbiochemicalreactionsinvolveseveralenzymesthatreducecarbonbyhydrogentransferandrearrangethecarboncompoundstosynthesizecarbohydrates.Thecarbonreductioncycleinvolvesthetransferofchemicalbondenergyandrearrangementofchemicalbonds.
6.Inanoxygenicphotosyntheticorganisms[42],waterisnotusedastheelectrondonor.E
43
lectronflowiscyclicandisdrivenbyasinglephotosystem,producingaprotonelectrochemicalgradientthatisusedtoprovideenergyforthereductionofNAD+byanexternalHatomoredonor(e.g.H2Soranorganicacid)inaprocessknownas“reverseelectronflow[43]”.FixationofCO2occursviadifferentpathwaysindifferentorganisms.
Notes
[1]blackbody(光、热)黑体
[2]incident[5insidd[nt]adj.[物]入 射
的
[3]scheme[ski:m]n.方案,图解
[4]anoxygenic[An7Rksi5dVenik]adj.非放氧的
[5]prochlorophyte[pr[u5klR:r[7fait]n.前绿色植物
[6]lightreaction光反应
[7]darkreaction暗反应
[8]embed[im5bed]vt.使插入,使嵌入,
深留,嵌入,[医]包埋
[9]orientation[7R:rien5teiF[n]n.方
向,方位,定位,倾向性,向东方
[10]asymmetrical[[5simitrik[l]adj.不
均匀的,不对称的
[11]electrochemicalgradient [i9lektr[u5kemik[l5greidi[nt]n.电化学梯度
[12]lace[leis]vt.扎 带 子,扎,饰 以 花 边
vi.缚带子
[13]scaffold[5skAf[ld]n.支架
[14]plastoquinone[5plAst[ukwin[un]n.质体醌
[15]ubiquinone[ju:5bikwin[un]n.泛醌
[16]photon[5f[utRn]n.光子
[17]antennapigment[An5ten[5pigm[nt]
n.天线色素
[18]antennasystem天线(色素)系统
[19]bacteriochlorophyll[bAkti[ri[5klR:r[fil]n.细菌叶绿素
[20]carotenoid[k[5rRt[nRid]n.类胡萝卜
素
[21]anchor[5ANk[]v.抛锚,锚定n.锚
[22]reactioncenter作用中心
[23]exciton[5iksitRn]n.激子,激发子
[24]fluorescence[flu[5resns]n.荧光
[25]primaryphotochemicalreaction原 初
光化学反应
[26]primarychargeseparation原初电荷分离
[27]energetically[7en[55dVetik[li]adv.在能学上
[28]oxygenicphotosyntheticorganism 放
氧光合生物
[29]photosystem 光系统
[30]concurrently[k[n5kQr[nntli]adv.同
时发生地,并发地
[31]intermediate[7int[5mi:dj[t]adj.中间
的
[32]redoxfreeenergy氧还自由能
[33]ATPSynthaseATP合酶
[34]phosphategrouptransferpotential磷
酸基团转移势
[35]quinine[kwi5ni:n]n.奎宁,奎宁化合
物
[36]pheophytin[7fi:[5faitin]n.脱镁叶绿
素
[37]tyrosine[5tir[si:n]n.酪氨酸
[38]flavoprotein[7fleiv[u5pr[uti:n]n.黄
素蛋白
[39]Calvincycle卡尔文循环
[40]photosyntheticcarbonreductioncycle光合碳还原循环
[41]Rubisco(Dribulose1,5bisphosphate
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
44
carboxylase/oxygenase) [ru5biskk[u]1,5二 磷 酸 核 酮 糖 羧 化 酶/加 氧
酶
[42]anoxygenicphotosyntheticorganisms非放氧光合生物
[43]reverseelectronflow反向电子流
犈狊狊犪狔15 犇犲狊犲狉狋犘犾犪狀狋犛狌狉狏犻狏犪犾
1.Desertplantshaveadaptedtotheextremesofheatandaridity[1]byusingbothphysicalandbehavioralmechanisms,muchlikedesertanimals.Plantsthathaveadaptedbyalteringtheirphysicalstructurearecalledxerophytes[2].Xerophytes,suchascacti[3],usuallyhavespecialmeansofstoringandconservingwater.Theyoftenhavefewornoleaves,whichreducetranspiration.Phreatophytes[4]areplantsthathaveadaptedtoaridenvironmentsbygrowingextremelylongroots,allowingthemtoacquiremoistureatornearthewatertable.
2.Otherdesertplants,usingbehavioraladaptations,havedevelopedalifestyleinconformancewiththeseasonsofgreatestmoistureand/orcoolesttemperatures.Thesetypesofplantsareusually(andinaccurately)referredtoasperennials[5],plantsthatliveforseveralyears,andannuals[6],plantsthatliveforonlyaseason.
3.Desertperennialsoftensurvivebyremainingdormantduringdryperiodsoftheyear,
thenspringingtolifewhenwaterbecomesavailable.4.Mostannualdesertplantsgerminateonlyafterheavyseasonalrain,andthencompletetheirreproductivecycleveryquickly.Theybloomprodigiouslyforafewweeksinthespring,accountingformostoftheannualwildflowerexplosionsofthedeserts.Theirheatanddroughtresistantseedsremaindormantinthesoiluntilthenextyear’sannualrains.
Xerophytes5.Thephysicalandbehavioraladaptationsofdesertplantsareasnumerousandinnovativeasthoseofdesertanimals.Xerophytes,plantsthathavealteredtheirphysicalstructuretosurviveextremeheatandlackofwater,arethelargestgroupofsuchplantslivinginthedesertsoftheAmericanSouthwest.Eachofthefoursouthwesterndesertsoffershabitatsinwhichmostxerophyticplantssurvive.Buteachischaracterizedbyspecificplantsthatseemtothrive[7]there.TheGreatBasinDesert[8]isnotedforvastrollingstandsofSagebrush[9]andSaltbush[10],whileintheMojaveDesert[11]JoshuaTrees[12],
CreosoteBush[13]andBurroweed[14]predominate.TheSonoranDeserts[15]hometoanincrediblevarietyofsucculents[16],includingthegiantSaguaroCactus[17],aswellasshrubsandtreeslikemesquite[18],Paloverde[19],andIronwood[20].TheChihuahuaDesert[21]isnotedformesquitegroundcoverandshrubbyundergrowth,suchasYucca[22]
andPricklyPearCactus[23].Cactus,xerophyticadaptationsoftherosefamily,area
45
mongthemostdroughtresistantplantsontheplanetduetotheirabsenceofleaves,
shallowrootsystems,abilitytostorewaterintheirstems,spinesforshadeandwaxyskintosealinmoisture.CactioriginatedintheWestIndies[24]andmigratedtomanypartsoftheNew World[25],populatingthedesertsoftheSouthwestwithhundredsofvarieties,suchastheBeavertailCactus[26]andJumpingCholla[27].Cactidependonchlorophyllintheoutertissueoftheirskinandstemstoconductphotosynthesisforthemanufactureoffood.Spinesprotecttheplantfromanimals,shadeitfromthesunandalsocollectmoisture.Extensiveshallowrootsystemsareusuallyradial,allowingforthequickacquisitionoflargequantitiesofwaterwhenitrains.Becausetheystorewaterinthecoreofbothstemsandroots,cactiarewellsuitedtodryclimatesandcansurviveyearsofdroughtonthewatercollectedfromasinglerainfall.
6.Manyotherdeserttreesandshrubshavealsoadaptedbyeliminatingleaves—replacingthemwiththorns,notspines—orbygreatlyreducingleafsizetoeliminatetranspiration.Suchplantsalsousuallyhavesmooth,greenbarkonstemsandtrunksservingtobothproducefoodandsealinmoisture.
Phreatophytes7.Phreatophytes,likethemesquitetree,haveadaptedtodesertconditionsbydevelopingextremelylongrootsystemstodrawwaterfromdeepundergroundnearthewatertable[28].Themesquite’srootsareconsideredthelongestofanydesertplantandhavebeenrecordedaslongas80feet.
8.Botanistsdonotagreeontheexactclassificationofthethreemesquitetrees:theHoneyMesquite[29],ScrewBeanMesquite[30]andtheVelvetMesquite[31],butnoonedisputesthesuccessoftheiradaptationtothedesertenvironment.Mesquitesareabundantthroughoutallthesouthwesterndeserts.TheCreosoteBushisoneofthemostsuccessfulofalldesertspeciesbecauseitutilizesacombinationofmanyadaptations.Insteadofthorns,itreliesforprotectiononasmellandtastewildlifefindunpleasant.Ithastinyleavesthatclosetheirstomata(pores)duringthedaytoavoidwaterlossandopenthematnighttoabsorbmoisture.Creosotehasanextensivedoublerootsystem,bothradialanddeep,toaccumulatewaterfrombothsurfaceandgroundwater.
Perennials9.Someperennials,suchastheOcotillo[32],survivebybecomingdormantduringdryperiods,thenspringingtolifewhenwaterbecomesavailable.Afterrainfalls,theOcotilloquicklygrowsanewsuitofleavestophotosynthesizefood.Flowersbloomwithinafewweeks,andwhenseedsbecomeripeandfall,theOcotillolosesitsleavesagainandreentersdormancy.Thisprocessmayoccurasmanyasfivetimesayear.TheOcotilloalsohasawaxycoatingonstems,whichservetosealinmoistureduringperiodsofdormancy.
10.Anotherexampleofperennialsthatutilizedormancy[33]asameansofevadingdrought
UNIT04 犅犗犜犃犖犢犃犖犇犘犔犃犖犜犘犎犢犛犐犗犔犗犌犢
46
arebulbs[34],membersofthelilyfamily[35].Thetopsofbulbsdryoutcompletelyandleavenotraceoftheirexistenceabovegroundduringdormantperiods.Theyareabletostoreenoughnourishment[36]tosurviveforlongperiodsinrockyoralluvial[37]soils.TheDesertLily,alsoknownastheAjo,isfoundatadepthof18inchesormore.Adequatewinterrainscanrouseittolifeafteryearsofdormancy.
Annuals(Ephemerals[38])
11.Theterm“annuals”impliesbloomingyearly,butsincethisisnotalwaysthecase,desertannualsaremoreaccuratelyreferredtoas“ephemerals.”Manyofthemcancompleteanentirelifecycleinamatterofmonths,someinjustweeks.
12.Contrarytotheusualideathatdesertsareuniformlyhot,dryandhomogeneousintheirlackofplantlife,theyareactuallybiologicallydiverseandcompriseamultitudeofmicroclimates[39]changingfromyeartoyear.Eachseason’suniqueprecipitation[40]patternfallsonahugevarietyofminienvironments[41].Andeachyearineachofthesetinyeconiches[42],adifferentmedley[43]ofplantsbloomasdifferentspeciesthrive.
13.Desertplantsmustactquicklywhenheat,moistureandlightinformthemit’stimetobloom.Ephemeralsarethesprintersoftheplantworld,sendingflowerstalksjettingoutinafewdays.Thepeakofthisbloommaylastforjustdaysormanyweeks,dependingontheweatheranddifferenceinelevation.Thehigheronegoes,thelaterbloomscome.
14.Differentvarietiesofplantswillbeinbloomfromdaytoday,andevenhourtohour,
sincesomeopenearlyandotherslaterintheday.EphemeralssuchastheDesertSandVerbena[44],DesertPaintbrush[45]and MojaveAster[46]usuallygerminate[47]inthespringfollowingwinterrains.Theygrowquickly,flowerandproduceseedsbeforedyingandscatteringtheirprogenytothedesertfloor.Theseseedsareextremelyhardy[48].Theyremaindormant,resistingdrought[49]andheat,untilthefollowingspring—sometimes2or3springs— whentheyrepeatthecycle,germinatingafterwinterrainstobloomagaininthespring.TherearehundredsofspeciesofephemeralsthatthriveinthedesertsoftheAmericanSouthwest.
15.Ifyouexaminedesertsoilsclosely,youwilldispelforeveranynotion[50]youmighthaveofthedesertasabarren[51]environment,foryouwilllikelyfinddozensofbothannualandperennialseedsineveryhandfulofdesertsoil.IntheSonoranDesert,seeddensitiesaveragebetween5,000and10,000persquaremeter.Theworldrecordisover200,000seedspersquaremeter.
Notes
[1]aridity[A5riditi]n.干燥
[2]xerophyte[5zi[r[fait]n.旱生植物
[3]cactus[5kAkt[s]n.仙人掌
[4]phreatophyte[fri:5At[7fait]n.(根
47
深达地下潜水层的)地下水湿生植物
[5]perennial[p[5renj[l]n.多年生植物
[6]annual[5Anju[l]n.一年生植物
[7]thrive[Wraiv]v.兴旺,繁荣,旺盛
[8]TheGreatBasinDesert(北美)大盆地
荒漠
[9]sagebrush[5seidVbrQF]n.山艾树
[10]saltbush[5sRlt7buF]n.[植]滨藜
[11]theMojave[m[u5hB:vi]Desert莫哈
维沙漠(在美国加利福尼亚西南)[12]Joshua[5dVRFw[]Trees约书亚树
[13]creosote[5kri[s[ut]Bush石炭酸灌木
[14]burroweed[5bQr[uwi:d]木碱蓬
[15]TheSonoran[sR:5nR:rB:]Desert索
诺兰沙漠
[16]succulent[5sQkjul[nt]n.肉 质 植 物,多汁植物adj.多 汁 的,多 水 分 的,多
汁性的
[17]Saguaro[s[5gwB:r[u]Cactus树形仙
人掌
[18]mesquit[meskwit]n.牧豆树;豆科灌
木
[19]paloverde[7pAl[u5v[:d]n.[植]假紫
荆属树木
[20]ironwood[5ai[wJd]n.铁木,硬木
[21]TheChihuahua[tFi5wB:w[:]Desert奇华华荒漠;Chihuahua吉娃娃(一 种
产于墨西哥的狗)[22]yucca[5jQk[]n.丝兰(一种丝兰属常
绿植物)[23]PricklyPearCactus刺梨仙人掌
[24]theWestIndies西印度群岛
[25]theNewWorld新世界(即美洲大陆)[26]beavertail[5bi:v[teil]Cactus獭 尾 仙
人掌
[27]JumpingCholla[5tF[uj[]跳月掌(这
种仙人掌 看 起 来 就 像 在 山 谷 中 跳 跃 一
样)
[28]watertable地下水位
[29]HoneyMesquiten.蜜豆灌木
[30]ScrewBeanMesquiten.一种豆科灌木
[31]theVelvetMesquite天鹅绒豆灌木
[32]Ocotillo[[U9k[5ti:l[U]n.墨西哥刺
木(一种仙人掌)[33]dormancy[5dR:m[nsi]n.休眠
[34]bulb[bQlb]n.鳞茎植物;鳞茎
[35]lilyfamily百合科
[36]nourishment[5nQriFm[nt]n.食 物,营养品
[37]alluvial[[5lu:vj[l]adj.冲 积 的,淤
积的
[38]ephemeral[i5fem[r[l]n.短 命 植 物
adj.朝生暮死的,短暂的,短命的
[39]microclimate [5maikr[Jklaimit]n.[气]小气候(指森林、城市、洞穴等局部
地区的气候)[40]precipitation[pri7sipi5teiF[n]n.降
水
[41]minienvironment微环境
[42]econiche[5i:k[unitF]n.生态小生境
[43]medley[5medli]n.混杂的人群,杂乱
的一团,混 合 物,杂 录,[音]集 成 曲
adj.混合的,拼凑的
[44]DesertSandVerbena[v[:55bi:n[]荒
漠黄花秋水仙
[45]DesertPaintbrush荒漠画笔树
[46]MojaveAster[5Ast[]摩哈比菊花
[47]germinate[5dV[:mineit]v.萌发
[48]hardy[5hB:di]adj.难的,艰苦的,勇敢的,抗性强的
[49]droughtn.干旱
[50]notion[5n[uF[n]n.概念,观念,想
法,意见,打算,主张
[51]barren[5bAr[n]adj.不 生 育 的,不
孕的,贫瘠 的,没 有 结 果 的,无 益 的,单调的,无聊的,空洞的
48
犝犖犐犜05 犌犈犖犈犜犐犆犛犃犖犇犈犞犗犔犝犜犐犗犖
犈狊狊犪狔16 犕犲狀犱犲犾’狊犌犲狀犲狋犻犮犔犪狑狊
1.Onceuponatime(1860’s),inanAustrianmonastery[1],therelivedamonknamedMendel,GregorMendel[2].MonkshadalotoftimeontheirhandsandMendelspenthistimecrossingpeaplants.Ashedidthisoverandoveragain,henoticedsomepatternstotheinheritanceoftraits[3]fromonesetofpeaplantstothenext.Bycarefullyanalyzinghispeaplantnumbers(hewasreallygoodatmathematics),hediscoveredthreelawsofinheritance:theLawofDominance[4],theLawofSegregation[5]andtheLawofIndependentAssortment[6].
2.Now,noticeinthatverybriefdescriptionofhisworkthatthewords“chromosomes”or“genes”arenowheretobefound.Thatisbecausetheroleofthesethingsinrelationtoinheritancehadnotbeendiscoveredyet.WhatmakesMendel’scontributionssoimpressiveisthathedescribedthebasicpatternsofinheritancebeforethemechanism[7]forinheritance(namelygenes)wasevendiscovered.
TheLawofDominance— Mendel’sFirstLaw3.Stated“simply”,itgoeslikeso:Inacrossofparentsthatarepureforcontrastingtraits[8],onlyoneformofthetraitwillappearinthenextgeneration.Offspringthatarehybridforatraitwillhaveonlythedominanttrait[9]inthephenotype[10].
4.WhileMendelwascrossinghispeaplants,henoticedsomethinginteresting.Whenhecrossedpuretallplantswithpureshortplants,allthenewpeaplants(referredtoastheF1generation)weretall.Similarly,crossingpureyellowseededpeaplantsandpuregreenseededpeaplantsproducedanF1generationofallyellowseededpeaplants.Thesamewastrueforotherpeatraits:
ParentPeaPlants F1PeaPlants
tallstem×shortstem alltallstems
yellowseeds×greenseeds allyellowseeds
greenpeapods[11]×yellowpeapods allgreenpeapods
roundseeds× wrinkled[12]seeds allroundseeds
axialflowers[13]×terminal[14]flowers allaxialflowers
So,whathenoticedwasthatwhentheparentplantshadcontrastingformsofatrait
49
(tallvsshort,greenvsyellow,etc.)thephenotypesoftheoffspringresembledonlyoneoftheparentplantswithrespecttothattrait.
5.Now,inourmodernwisdom,weuse“allele”[15]or“gene”insteadofwhatMendelcalled“factors”.ThereisageneintheDNAofpeaplantsthatcontrolsplantheight(makesthemeithertallorshort).Oneformofthegene(allele)codes[16]fortallandtheotheralleleforplantheightcodesforshort.Forabbreviations,weusethecapital“T”forthedominanttallallele,andthelowercase[17]“t”fortherecessive[18]shortallele.Let’srevisitthethreepossiblegenotypes[19]forpeaplantheightandaddsomemorevocabulary.
GenotypeSymbol GenotypeVocab Phenotype
TT homozygous[20]DOMINANTorpuretall tall
Tt heterozygous[21]orhybrid tall
tt homozygousRECESSIVEorpureshort short
Note:theonlywaytherecessivetraitshowsupinthephenotypeisifthegenotypehas2lowercaseletters(i.e.ishomozygousrecessive).Alsonote:hybridsalwaysshowthedominanttrait[22]intheirphenotype(that,bytheway,isMendel’sLawofDominance).
TheLawofSegregation — Mendel’sSecondLaw6.Duringtheformationofgametes(eggsorsperm),thetwoallelesresponsibleforatrait,areseparatedfromeachother.Allelesforatraitarethen“recombined”atfertilization,producingthegenotypeforthetraitsoftheoffspring.
Parents F1Offspring
Genotype(s) TT×tt 100% Tt
Phenotype(s) tall×short 100%tall
So,hetakestwoofthe“F1”generation(whicharetall)andcrossesthem.Hewasprobablyfiguringthathe’sgonnagetalltallagain(sincetallisdominant).Butno!Hegotsomeshortplantsfromthiscross!Hisnewbatchofpeaplants(the“F2”generation)isabout3/4talland1/4short.
ParentPeaPlants(TwoMembersofF1Generation) Offspring(F2Generation)
Genotypes:
Tt× Tt
Phenotypes:
tall×tall
Genotypes:
25% TT
50% Tt
25%tt
Phenotypes:
75%tall
25%short
TheLawofIndependentAssortment— Mendel’sThirdLaw7.Allelesfordifferenttraitsaredistributedtosexcellsindependentlyofoneanother.So
UNIT05 犌犈犖犈犜犐犆犛犃犖犇犈犞犗犔犝犜犐犗犖
50
farwe’vebeendealingwithonetraitatatime.Forexample,height(tallorshort),
seedshape(roundorwrinkled),podcolor(greenoryellow),etc.Mendelnoticedduringallhisworkthattheheightoftheplantandtheshapeoftheseedsandthecolorofthepodshadnoimpact[23]ononeanother.Inotherwords,beingtalldidn’tautomaticallymeantheplantshadtohavegreenpods,nordidgreenpodshavetobefilledonlywithwrinkledseeds,thedifferenttraitsseemtobeinheritedindependently.
8.Pleasenotetheemphasisontheword“different”.Ninetimesoutoften,inaquestioninvolvingtwodifferenttraits,youranswerwillbe“independentassortment”.Itinvolveswhat’sknownasa“dihybridcross”[24],meaningthattheparentsarehybridfortwodifferenttraits.
9.Thegenotypesofourparentpeaplantswillbe:RrGg×RrGg,where“R”=dominantalleleforroundseeds,“r”=recessivealleleforwrinkledseeds,“G”=dominantalleleforgreenpods,and“g”=recessivealleleforyellowpods.
10.Noticethatwearedealingwithtwodifferenttraits:(1)seedtexture[25](roundorwrinkled),and(2)podcolor(greenoryellow).Noticealsothateachparentishybridforeachtrait(onedominant&onerecessivealleleforeachtrait).
11.Weneedto“split”thegenotypelettersandcomeupwiththepossiblegametesforeachparent.Keepinmindthatagamete(sexcell)shouldgethalfasmanytotalletters(alleles)astheparentandonlyoneofeachletter.Soeachgameteshouldhaveone“are”
andone“gee”[26]foratotaloftwoletters.Therearefourpossiblelettercombinations:
RG,Rg,rG,andrg.Thesegametesaregoing“outside”thepsquare[27],above4columnsandinfrontof4rows.Wefillthingsinjustlikebefore— “lettersfromtheleft,
lettersfromthetop”.Whenwefinisheachbox,wegetsfourletterstotal(two“are’s”
andtwo“gees”).Thisiswhatitlookslike:
RG Rg rG rg
RGRRGGround
RRGground
RrGGround
RrGground
RgRRGground
RRgground
RrGground
Rrgground
rGRrGGround
RrGground
rrGGwrinkled
rrGrwrinkled
rgRrGground
Rrgground
rrGgwrinkled
rrggwrinkled
12.Theresultsfromadihybridcrossarealwaysthesame:9/16boxes(offspring)showdominantphenotypeforbothtraits(roundandgreen),3/16showdominantphenotypeforfirsttraitandrecessiveforsecond(roundandyellow),3/16showrecessivephenotypeforfirsttrait&dominantformforsecond(wrinkledandgreen),and1/16showrecessiveformofbothtraits(wrinkledandyellow).
13.So,asyoucanseefromtheresults,agreenpodcanhaveroundorwrinkledseeds,and
51
thesameistrueofayellowpod.Thedifferenttraitsdonotinfluencetheinheritanceofeachother.Theyareinheritedindependently.
14.Interestingtonoteisthatifyouconsideronetraitatatime,wegettheusual3∶1ratioofasinglehybridcross.Forexample,justcomparethecolortraitintheoffspring:12greenand4yellow (3∶1dominant:recessive).Samedealwiththeseedtexture:12round&4wrinkled(3∶1ratio).Thetraitsareinheritedindependentlyofeachother.
Notes
[1]monastery[5mRn[stri]n.修道院,僧
侣
[2]GregorMendel孟 德 尔(1822~1884)奥地利遗传学家
[3]trait[treit]n.性状
[4]theLawofDominance[5dRmin[ns]显性定律
[5]theLawofSegregation[7segri5geiF[n]分离定律
[6]theLawofIndependentAssortment[[5sR:tm[nt]独立分配定律
[7]mechanism[5mek[niz[m]n.机制
[8]contrastingtrait相对性状
[9]dominanttrait显性性状
[10]phenotype[5fi:n[taip]n.表型
[11]pod[pRd]n.豆荚
[12]wrinkled[5riNkld]adj.具皱的
[13]axialflowers茎间花
[14]terminalflowers茎顶花
[15]allele[[5li:l]n.等位基因
[16]code[k[ud]v.编码
[17]lowercase小写字母
[18]recessive[ri5sesiv]adj.隐性的
[19]genotype[5dVen[taip]n.基因型
[20]homozygous[7hRm[5zaig[us]adj.纯
合的
[21]heterozygous[7het[r[u5zaig[s]adj.杂合的
[22]dominanttrait显性性状
[23]impact[5impAkt]n.碰撞,冲击,冲
突,影响,效果
[24]dihybrid[dai5haibrid]cross双因子杂
种杂交
[25]texture[5tekstF[]n.纹理
[26]one“are”andone“gee”一个R或r和
一个G或g[27]psquaren.P方阵
犈狊狊犪狔17 犠犺犪狋犻狊犪犌犲狀犲狋犻犮犕犪狆[1]?
1.Ageneticlinkagemap[2]showstherelativelocationsofspecificDNAmarkers[3]along
thechromosome.Eachmarkerislikeamilemarker[4]alongahighway.Anyinherited
physicalormolecularcharacteristicthatdiffersamongindividualsandiseasilydetecta
bleisapotentialgeneticmarker[5].MarkerscanbeexpressedDNAregions(genes)or
DNAsegmentsthathavenoknowncodingfunctionbutwhoseinheritancepattern[6]can
befollowed.DNAsequencedifferencesareespeciallyusefulmarkersbecausetheyare
UNIT05 犌犈犖犈犜犐犆犛犃犖犇犈犞犗犔犝犜犐犗犖
52
plentifulandeasytocharacterizeprecisely.Markersmustbepolymorphic[7]tobeusefulinmapping;thatis,alternativeforms(alleles)mustexistamongindividualssothattheyaredetectableamongdifferentmembersinthemappingpopulation[8].
2.Amappingpopulationisthegroupofindividualsthatwillbeevaluatedfortheir“score”
atasetofmarkers.Thisrawmappingdataisanalyzedbysoftware,whichconstructsthemapbyobservinghowfrequentlytheallelesatanytwomarkersareinheritedtogether.Thecloserthemarkersare,thelesslikelyitisthatarecombinationevent[9](acrossover[10]duringmeiosis)willseparatethealleles,andthemorelikelyitisthattheywillbeinheritedtogether.Thus,unlikeothertypesofmaps,thedistancebetweenpointsonageneticmapisnotmeasuredinanykindofphysicalunit;itisareflectionoftherecombinationfrequency[11]betweenthosetwopoints.Thisgeneticmapunitismeasuredintermsofcentimorgans(cM)[12](namedafterthegeneticistThomasHuntMorgan[13]).Twomarkersaresaidtobe1cMapartiftheyareseparatedbyrecombination1% ofthetime.Thegeneticdistance[14]tellsyoulittleaboutthephysicaldistance[15]—theactualamountofDNAseparatingthemarkers.Thisgenetictophysicaldistancerelationshipvariesbetweenspecies,andvariesbetweendifferentspotswithinthegenomeofasinglespecies.
3.Ageneticmaphelpsusunderstandthestructure,functionandevolutionofthegenome.Itcanbeanimportanttoolforagriculturalcropimprovement.Recentworkhasshownthatthegeneticmapsofmanycloselyrelatedspecies(forexample,thegrains)arequitesimilarwithrespecttothecontentandlocationofgenes,andscientistsaretryingtodeterminehowthegeneticmapofonespeciesmaybeappliedtoothers.
4.Manydifferenttypesofobjectscanbeassignedapositiononageneticmap.Wewilldividetheseobjectsintotwocategories:“point”objectsand“interval”objects.Knowngenesandmolecularmarkersareexamplesofpointonmaps.Centromeres[16],quantitativetraitloci(QTLs)[17],rearranements,introgressions[18],syntenic[19]regionsandcontigs[20]couldbeexamplesofintervals.
5.Noteverydatabasewillcontainallthesetypesofobjects,orrepresentthesameobjectinthesameway!Forexample,incertaindatabases,aQTLmaybeassignedaspecificpointlocationonamap;inothers,aQTLmaybedefinedtospanaparticularregionofthemap.
Notes
[1]geneticmapn.遗传图
[2]geneticlinkagemapn.遗传连锁图
[3]specificDNAmarkern.特异DNA标
记
[4]milemarkern.里程计
[5]geneticmarkern.遗传标记
[6]inheritancepattern[in5herit[ns5pAt[n]n.遗传模式
[7]polymorphic[9pRli5mC:fik]adj.多
态性的
53
[8]mappingpopulationn.作图群体
[9]recombinationeventn.重组事件
[10]crossovern.交叉
[11]recombinationfrequencyn.重组频率
[12]centimorgan(cM)[senti5mR:g[n]n.(遗)厘摩(基因交换单位)
[13]ThomasHuntMorgann.摩尔根(1866~1946),美 国 细 胞 遗 传 学 家。他 提 出
了“基因论”,他认为基因在染色体上呈
直线排列,从而确立了不同基因与性状
之间的对应关系。
[14]geneticdistancen.遗传距离
[15]physicaldistancen.物理(实际)距离
[16]centromere[5sentr[7mi[]n.(染色体
上的)着丝粒
[17]quantitativetraitloci [5l[usai](QTLs)n.数量性状位点
[18]introgression[7intr[5greF[n]n.基因
渗入,渐渗现象
[19]syntenic[sin5tenik]adj.基因共线
[20]contig[k[ntig]n.重叠群
犈狊狊犪狔18 犅犻狅犾狅犵犻犮犪犾犈狏狅犾狌狋犻狅狀
1.Conceptthatembodiesthebeliefthatexistinganimalsandplantsdevelopedbyaprocessofgradual,continuouschangefrompreviouslyexistingforms,thistheory,alsoknownasdescentwithmodification[1],constitutesorganicevolution[2].Inorganicevolution[3],
ontheotherhand,isconcernedwiththedevelopmentofthephysicaluniversefromunorganizedmatter.Organicevolution,asopposedtobeliefinthespecialcreationofeachindividualspeciesasanimmutable[4]form,conceivesoflifeashavinghaditsbeginningsinasimpleprimordialprotoplasmicmass[5](probablyoriginatinginthesea)fromwhich,throughthelongerasoftime,aroseallsubsequentlivingforms.
HistoryofEvolutionaryTheory —EarlyTheories2.EvolutionaryconceptsappearedinsomeearlyGreekwritings,e.g.intheworksofThales[6],Empedocles[7],Anaximander[8],andAristotle[9].Undertherestraining[10]
influenceoftheChurch,noevolutionarytheoriesdevelopedduringsome15centuriesoftheChristianera[11]tochallengethebeliefinspecialcreationandtheliteralinterpretationofthefirstpartofGenesis[12];however,muchdatawasaccumulatedthatwastobeutilizedbylatertheorists[13].Withthegrowthofscientificobservationandexperimentation,therebegantoappearfromaboutthemiddleofthe16thcentury.Glimpsesofthetheoryofevolutionemergedinthemid19thcentury.Theinventionofthemicroscope,makingpossiblethestudyofreproductivecellsandthegrowthofthescienceofembryology[14],wasafactorinoverthrowinghampering[15]theoriesfoundedinfalseideasofthereproductiveprocess;studiesinclassification(taxonomy[16]orsystematics[17])
andanatomy,basedondissection[18],werealsoinfluential.3.Linnaeus[19],inhislateryears,showedaninclinationtowardbeliefinthemutabilityofspeciesasaresultofhisobservationsofthemanyvariationsamongspecies.Buffon[20],
UNIT05 犌犈犖犈犜犐犆犛犃犖犇犈犞犗犔犝犜犐犗犖
54
onthebasisofhisworkincomparativeanatomy,suggestedtheinfluenceofuseanddisuse[21]inmoldingtheorgansofvertebrateanimals.Lamarck[22]wasthefirsttopresentaclearlystatedevolutionarytheory,butbecauseitincludedtheinheritanceofacquiredcharacteristics[23]astheoperativeforce[24]ofevolution,hiswholetheorywasridiculedanddiscredited[25]formanyyears.
Darwinism[26]
4.Althoughspecialcreationofeachspecieswastheprevalent[27]beliefevenamongscientistsinthefirsthalfofthe19thcentury,theevidenceinfavorofevolutionhadbythattimebeenuncovered.Itremainedforsomeonetoassembleandinterprettheevidenceandtoformulateascientificallycredible[28]theory.ThiswasaccomplishedsimultaneouslybyA.R.Wallace[29]andCharlesRobertDarwinwhosetforththeconceptsthatcametobeknownasDarwinism.In1859appearedthefirsteditionofDarwin’sOriginofSpecies[30].Theinfluenceofthisevolutionarytheoryuponscientificthoughtandexperimentationcannotbeoverestimated.Intheyearsfollowingthepromulgation[31]ofDarwin’stheoryofevolution,manyacceptedandmanydenieditsvalidity[32].
5.Thetheoryfoundanopposingforceinsomereligiouscreeds[33]thatdeclareditincompatible[34]withtheirbasictenets[35].Foratimeevolution,sometimesfalselyinterpretedasmeaninghumandescentfrommonkeysratherthandescentfromanancientandextinctancestor,becameatargetforattackbybothchurchandeducationalauthorities.FeelingranhighevenaslateasthetimeoftheScopestrial[36].Nevertheless,thetheoryofevolutionbecamefirmlyentrenched[37]asascientificprinciple,andinmostcreedsithasbeenreconciled[38]withreligiousteachings.SomeChristianfundamentalists[39],
however,donotacceptthetheoryandhavestriventohavebiblicalcreationism[40]
taughtintheschoolsasanalternativetheory.
ModernEvolutionaryTheory6.Evolutionarytheoryhasundergonemodificationinthelightoflaterscientificdevelopments.Asmoreandmoreinformationhasaccumulated,thefactsfromanumberoffieldsofinvestigationhaveprovidedcorroboration[41]andmutualsupport.EvidencethatevolutionhasoccurredstillrestssubstantiallyonthesamegroundsthatDarwinemphasized;comparativeanatomy,embryology,geographicaldistribution[42],andpaleontology[43].Butadditionalrecentevidencehascomefrombiochemistryandmolecularbiology,whichrevealsfundamentalsimilaritiesandrelationsinmetabolismandhereditarymechanismsamongdisparate[44]typesoforganisms.Ingeneral,bothatthevisiblelevelandatthebiochemical,onecandetectthekindsofgradationsofrelatednessamongorganismsexpectedfromevolution.
7.ThechiefweaknessofDarwinianevolutionlayingapsinitsexplanationsofthemechanismofevolutionandoftheoriginofspecies.TheDarwinianconceptofnaturalselectionisthatinheritablevariationsamongtheindividualsofgiventypesoforganismscon
55
tinuallyariseinnatureandthatsomevariationsproveadvantageousunderprevailingconditionsinthattheyenabletheorganismtoleaverelativelymoresurvivingoffspring.ButhowthesevariationsinitiallyariseoraretransmittedtooffspringandhencetosubsequentgenerationswerenotunderstoodbyDarwin.Thescienceofgenetics,originatingatthebeginningofthe20thcenturywiththerecognitionoftheimportanceoftheearlierworkofMendel,providedasatisfactoryexplanationfortheoriginandtransmissionofvariation.In1901,deVries[45]presentedhistheorythatmutation,orsuddenlyappearingandwelldefinedinheritablevariation(asopposedtotheslight,cumulativechangesstressedbyDarwin),isaforceintheoriginandevolutionofspecies.Mutationingenesisnowacceptedbymostbiologistsasafundamentalconceptinevolutionarytheory.Thegeneisthecarrierofheredityanddeterminestheattributesoftheindividual;thuschangesinthegenescanbetransmittedtotheoffspringandproduceneworalteredattributesinthenewindividual.
8.Stillprevalentmisunderstandingsofevolutionarethebeliefsthatananimalorplantchangesinordertobetteradapttoitsenvironment—forexample,thatitdevelopsaneyeforthepurposeofseeing—andthatactualphysicalcompetitionamongindividualsisrequired.Sincemutationisarandomprocess,changescanbeuseful,unfavorable,orneutraltotheindividual’sorspecies’survival.However,anewcharacteristicthatisnotdetrimental[46]maysometimesbetterenabletheorganismtosurviveorleaveoffspringinitsenvironment,especiallyifthatenvironmentischanging,ortopenetrate[47]
anewenvironment—suchasthedevelopmentofalunglikestructurethatenablesanaquaticanimaltosurviveonland(lungfish[48]),wheretheremaybemorefoodandfewerpredators.
Notes
[1]descentwithmodificationn.修饰演化
[2]organicevolutionn.有机进化
[3]inorganicevolutionn.无机进化
[4]immutable[i5mju:t[bl]adj.不 可 变
的,不变的,不能变的,永恒的
[5]primordial[prai5mR:dj[l]protoplasmicmassn.原始原生质浆
[6]Thales[5Weili:z]n.泰 利 斯(624~546BC),古希腊哲学家、数学家、天文
学家,希腊“七贤”之一。[7]Empedoclesn.恩 培 多 克 勒(493~433BC),古希腊哲学家。认为组成世界的
四大元素 分 别 是 火(fire)、水(water)、土(earth)和气(air)。
[8]Anaximandern.阿那克西曼德(约公元
前610年~前547年),古希腊哲学家、米 利 都 学 派 的 学 者、泰 勒 斯 的 学 生。据说他还是在希腊第一个绘 制 地 图 的
人。阿那克西曼德还 曾 经 担 任 过 一 个
米利都殖 民 地 的 领 袖。阿 那 克 西 曼 德
认为,构成万物的元素是所谓 的“无 限
者”,世 界 从 它 产 生,又 复 归 于 它。他
还认为,地 球 是 一 个 自 由 浮 动 的 圆 柱
体,人类处于圆柱体 的 一 端 表 面 之 上,而我 们 的 世 界 只 是 无 数 世 界 中 的 一
个。阿那 克 西 曼 德 还 认 为,人 从 海 鱼
演化而来。[9]Aristotle[5AristRtl]n.亚 里 士 多 德
UNIT05 犌犈犖犈犜犐犆犛犃犖犇犈犞犗犔犝犜犐犗犖
56
(公元前384~前322),古 希 腊 大 哲 学
家、科学家。[10]restraining[ristreiniN]adj.抑 制 的,
遏制的,控制的
[11]Christianera[5kristj[n5i[r[]公元纪
年,公元
[12]Genesis[5dVenisis]n.(圣经)创世记
[13]theorist[5Wi[rist]n.理论家,空谈家
[14]embryology[7embri5Cl[dVi]n.胚胎
学
[15]hamper[5hAmp[]v.妨碍,牵制
[16]taxonomy[tAk5sRn[mi]n.分类学
[17]systematics[7sisti5mAtiks]n.系 统
学 (=taxonomy)[18]dissection[di5sekF[n]n.解剖
[19]Linnaeus[li5ni:[s]n.林 奈(1707~1778)瑞典自然学者,奠 定 了 现 代 生 物
学分类命名的基础。[20]Buffon[5bu:f[u]n.布 丰(Georges
LouisLeclerc,ComtedeBuffon,1707~1788),法国 博 物 学 家、数 学 家、生 物
学家、宇 宙 学 家 和 作 家。布 丰 的 思 想
影响了 之 后 两 代 的 博 物 学 家,包 括 达
尔文和拉马克。[21]useanddisusen.用和废用
[22]Lamarck[l[5ma:k]n.拉马克 (法国
博物学家,1744~1829)[23]acquiredcharacteristicsn.获得性状
[24]operativeforcen.运转力
[25]discreditv.不信,怀疑
[26]Darwinism[5dB:winiz[m]n.达尔文
学说,进化论
[27]prevalent[5prev[l[nt]adj.普 遍 的,流行的
[28]credible[5kredibl]adj.可信的
[29]A.R.Wallacen.华莱士(A.R.AlfredRusselWallace,1823~1913)英 国 博
物学家、进 化 论 者,与C.R.达 尔 文 共
同提出 自 然 选 择 学 说,动 物 地 理 学 的
奠基人。[30]OriginofSpecies物种起源
[31]promulgation[9prCm[l5geiF[n]n.颁布
[32]validity[v[5liditi]n.有效性,合法性,正确性
[33]creed[kri:d]n.信条
[34]incompatible[7ink[m5pAt[bl]adj.不相容的
[35]tenet[5tenit]n.原则
[36]Scopestrial斯克普斯审判,著名的“猴
子”审判,即1925年田纳西州的斯克普
斯案的审判。当时田纳 西 州 通 过 了 一
部法律,禁 止 公 立 学 校 讲 授 达 尔 文 的
进化论。高 中 科 学 教 师、24岁 的 约 翰
·斯 克 普 斯(JohnT.Scopes)同 意 在
一个试 验 性 的 案 件 中 扮 演 被 告,充 当
牺牲的羔羊。这场审判 在 科 学 和 守 旧
的宗教之间引发了一场引人注 目 的 对
抗,案 件 审 判 轰 动 一 时。在 斯 克 普 斯
审判的 传 奇 故 事 中,该 案 是 一 个 转 折
点;斯克普斯输了,但是科学却赢了。[37]entrench[in5trentF]v.以壕沟防护
[38]reconcile[5rek[nsail]vt.使 和 解,使
和谐
[39]Christianfundamentalist [5kristj[
fQnd[5ment[list]n.信 奉 正 统 派 基 督
教的人
[40]biblicalcreationism[5biblik[lkri:5eiF[niz[m]n.(圣 经)创 造 宇 宙 说,特 别
创造说
[41]corroboration[k[rRb[5reiF[n]n.确
证的事实,确证
[42]geographicaldistributionn.地理分布
[43]paleontology[7pAliRn5tRl[dVi]n.古生物学
[44]disparate[5disp[rit]adj.全异的
[45]deVriesn.德弗里斯 (人名)[46]detrimental[7detri5mentl]adj.有 害
的
[47]penetrate[5penitreit]v.穿 透,渗 透,看穿,洞察
[48]lungfish[5lQNfiF]n.肺鱼
57
犝犖犐犜06 犎犝犕犃犖犃犖犃犜犗犕犢犃犖犇犘犎犢犛犐犗犔犗犌犢
犈狊狊犪狔19 犜犺犲犎狌犿犪狀犅狉犪犻狀
1.Thehumanbrain,whenexposed,looksratherlikeanenormouswalnut[1].Itweighsaboutthreeorthreeandahalfpoundsandismadeup,likeotherorgans,ofcells.Unlikeawalnut,ithasbeenmappedoutinminute[2]detail.
2.SincethemenwhofirstdissectedthebrainusedLatinandGreek,thevariouspartsofthebrainhaveLatinorGreeknames:thebrainitselfisthecerebrum[3]andthewrinkledouterlayeristhecortex[4];thesmallridgedprojectionatthebackiscalledthecerebellum[5](‘littlebrain’),andsoon.
3.Thecortex,about1or4mmthick,enclosesthetwomostnotablepartsofthebrainthecerebralhemispheres[6].These,almostbutnotquitemirrorimages[7]ofoneanother,togetherconstitutethecerebrum;andeachhemisphereinturnisdividedintolobes[8],the“continents”ofthecerebrum:atthefront,thefrontallobe[9];attheside,
thetemporallobe[10];ontop,theparietallobe[11];andatthebackofthehead,theoccipitallobe[12].Eachlobeisroughlyassociatedwithadifferentfunction.
4.Thetwohemispheresarejoinedbythickwhitishfibers,thecorpuscallosum[13];nearthemarethelimbiclobe[14](concernedwithemotion)andtheeggshapedthalamus[15]
(‘bedroom’!)nearthecenterofthebrain;belowthelatteristhehypothalamus[16]
whichisresponsibleforbodytemperature,amongotherthings.5.Themidbrainismuchsmaller.Amongitsdutiesareresponsestosightandsoundandcontrolofsleepingandwaking.Thehindbrainincludesthecerebellum(involvedinthemanagementofmovement)andthetinylumpsandbumpswhichhavefunctionstoonumeroustomention.
6.Midbrainandhindbrainareoftengroupedtogetherandcalledbrainstem[17],oneofthefeweasilyunderstoodtermsintheneurosciences[18].
7.Connectingthebrainstemtotherestofthebodyisthespinalcord[19].Partsofthespinalcordhavetheirownfunction:soldierstothebrain’sgeneral.Butmostlyitcontainsfiberswhichconnectthebraintomusclesandsenseorgansthroughoutthebody.
UNIT06 犎犝犕犃犖犃犖犃犜犗犕犢犃犖犇犘犎犢犛犐犗犔犗犌犢
58
Notes
[1]walnut[5wC:ln[t]n.胡桃,核桃树
[2]minute[mai5nju:t]adj.微 小 的,详
细的,仔细而准确的
[3]cerebrum[5seribr[m]n.大脑
[4]cortex[5kR:teks]n.皮层
[5]cerebellum[7seri5bel[m]n.小脑
[6]cerebralhemisphere[5seribr[l5hemisfi[]n.大脑半球
[7]mirrorimage[5mir[5imidV]n.镜像
[8]lobe[l[ub]n.脑叶
[9]frontal[5frQntl]lobe前叶
[10]temporal[5temp[r[l]lobe颞叶
[11]parietal[p[5rai[t[l]lobe顶叶
[12]occipital[Rk5sipitl]lobe枕叶
[13]corpuscallosum[5kR:p[skC:l[s[m]
n.胼胝体
[14]limbic[5limbik]lobe侧叶
[15]thalamus[5WAl[m[s]n.丘脑
[16]hypothalamus[7haip[u5WAl[m[s]
n.下丘脑
[17]brainstemn.脑干
[18]neuroscience[7nju[r[u5sai[ns]n.神
经科学
[19]spinal[5spainl]cordn.脊索
犈狊狊犪狔20 犇犻犪犵狀狅狊犻狊:犉犲犿犪犾犲
1.Medicalscienceislearningthatsexdoesmakeadifference.Men’sandwomen’sbodieseachhavetheirownhealthproblems,reactdifferentlytodrugsandoftenrequiredifferenttreatments.Webringyousomeofthelatestthinking:
ImmuneComplexity2.A woman’simmunesystemdisplaysanexquisite[1]amountofcontrolthataman’scan’treplicate.It’sstillnotclearwhy,butthefemalebody’sdefensestendtomountmoreaggressiveresponsestoinvadingmarauders[2];then,duringpregnancy,thisresponseisdampened(reduced)considerablytoaccommodate[3]thefetus[4].Perhapsowingtothisonoffintensity,womenaremorepronetodevelopinglupus[5],rheumatoidarthritis[6]andmultiplesclerosis[7],allconditionsinwhichtheimmunesystemattackshealthytissues.
3.Researchersarejustbeginningtostudywhyestrogen[8]mightcausethedefensesystemtorev[9]intooverdriveinthesecases.
HabitsoftheHeart4.Theclassicchestcrushing[10]painthatisthehallmark[11]ofaheartattackturnsouttobemainlyamalesymptom[12].Women’sheartattacks,bycontrast,tendtoshowupasshortnessofbreath,fatigueandjawpain,stretchedoutoverhoursratherthanmi
59
nutes.5.Womentendtosuffertheirfirstheartattack10yearsolderthanmen.Yet,partlybecausethewomenareolder,thoseheartattacksaremoreoftenfatal.Thisisapostmenopausal[13]phenomenon,atradeoff[14]foryearsofprotectionfromestrogen.Stayingbathedinthehormonekeepsbloodvesselselasticandfreeofhardened/plaqueformations.Estrogenalsoinstructsthelivertochurnout[15]moreHDL[16],orgoodcholesterol[17],whichpullsplaqueawayfromarterywalls.
6.Drugscommonlyusedtobreakupclotsandstabilizeerraticheartbeats[18]arelesseffectiveinwomenthaninmen.Hormonereplacementtherapy[19]withestrogenandprogestin[20]hasbeenshowntohelp.A USGovernmentstudyiscurrentlyunderwaythataimstoclarifyhowestrogenworksontheheart,brainandbreast.
ReproductiveOrgans7.Advancesindiagnosticexams[21]andhormonetreatmentshavedrasticallycuttheincidenceofcanceroftheuterus[22],ovaries[23]andcervix[24]overthepastfivedecades.Papsmears[25]thatdetectabnormalcellsinthecervixbeforetheybecomemalignant[26]havecontributedtoa75%dropincervicalcancer[27]sincethe1950s.Wideruseofbirthcontrolpillsandhormonereplacementtherapyhavedecreasedtheriskofovariananduterine[28]cancers.Recentresearchalsosuggeststhatinsomecases,alowfatdietcancuttheriskofcervicalcancerevenfurther.
RiskoftheKnee8.Aswomenparticipateinmoreandmoresports,orthopedists[29]arenoticingadifferenceinthetypesofinjurieswomenareproneto.Theyappeartobemoresusceptiblethanmentodamagingtheligaments[30]thatholdthekneetogether.Manywomenbasketball
playershavesufferedpainfulandpotentiallydebilitatingtears[31]totheanteriorcrusiateligament[32],whichcantakemonthstoheal.Doctorsthinkitmayhavesomethingtodowithawoman’swiderhips,whichplaceagreaterstrainontheligamentsjoiningthethigh[33]totheknee.Theseligamentsareweakerinwomentostartwith.
SlowerMetabolism9.Womentendtometabolizeanumberofdrugsdifferentlyfrommen:
Alcohol:ittakesfewerdrinksforawomantofeeltheeffects[34],becausetheliverbreaksdownalcoholmoreslowly,leavingmoreofitfloatingintheblood.Aspirin[35]:thepainkillertakeslongertoclearawoman’ssystem.Becauseitkeeps
platelets[36]fromclotting,aspirinshouldbeavoidedbypregnantwomen.Itcantriggerbleedinginthefetalbrain.Betablockers[37]:BecausedrugslikeInderal,prescribedtoreducebloodpressureandmigrainepain[38],takelongertometabolizeinwomenthaninmen,thedosagemustbe
UNIT06 犎犝犕犃犖犃犖犃犜犗犕犢犃犖犇犘犎犢犛犐犗犔犗犌犢
60
carefullymonitoredtoavoidsideeffects.TricyclicAntidepressants[39]:womentakingoralcontraceptives[40]mayneedlowerdosesofthesedrugstotreattheirdepression,sincethePill[41]keepslevelsofthedrugsinthebodyhigh.
MindandMood10.Womenaremorepronetodepressionthanmen,andthereasonmayhaveasmuchtodo
withbiologyasithaswithstressandotherlifestylefactors.Evidenceismountingthatthemaleandfemalebrainsmayresponddifferentlytohormonesandbrainchemicals.Womenproducelessserotonin[42],amoodregulatingchemical,thanmen,andaremoresensitivetochangesinserotoninlevels,whichareinturnregulatedbyestrogen.Womenthusrespondbettertodrugsaffectingtheserotoninsystem,whilementendtorespondbettertodrugsthatalsoaffectnorepinephrine[43],aneurotransmittersecretedbytheadrenalglands[44]andbynerveendingsduringstress.
11.Estrogenmaystaveoff[45]thedementia[46]andmemorylossofAlzheimer’sdiseasebyactuallyencouragingneuronsinthebraintogrownewnerveextensions.PostmenopausalwomenwhodonothavehormonereplacementtherapyhaveagreaterchanceofdevelopingAlzheimer’sandmemorylossthanmenofthesameage,whosetestisterone[47]
ismetabolizedintoestradiol[48],aformofestrogen.
BreastCancer12.Muchofthecurrentresearchisfocusingonearlydetection.Studiesshowthatwomen
withamputation[49]ineithergeneBRCA1orgeneBRCA2haveasmuchasa56%chanceofdevelopingbreastcancerbyage70.Thepredictivepowerofthegenes,however,isstillbeingdebated,asscientiststrytodeterminehowgenes,environmentandotherfactorsaffectingtheappearanceandgrowthoftumors.Treatmentoptionsareconstantlyexpanding,thankstobetterunderstandingofhowbesttocombinesurgery,drugs,
chemotherapy[50]andradiation.Newformsofestrogenlikesupplements,initiallydevelopedtopreventosteoporosis[51],appeartopreventthegrowthofbreasttumorsaswell,
andmorecomprehensivestudiesshowthatanolddrug,tamoxifen[52],cancuttheriskofcancerasmuchas45%overfouryears.
DigestiveSystem13.Evenifamanandawomaneatthesamething,itmaytakethewomanmuchlongerto
digestit.Thatleaveswomenthreetimesasvulnerabletochronicconstipation[53]asmenandtwiceaslikelytodevelopintestinaldisorders.Thesexdiscrepancy[54]apparentlystartswithchewing:preliminarystudiesshowthatfemalesaliva[55]differschemicallyfromthatofmen,perhapssettingthestage[56]forfood’sslowerjourneythroughawoman’sdigestivesystem.
61
CancerTypes14.TheProjectednumberofdeathsin1999:
WOMEN1.Lung&bronchus[57] 680002.Breast 433003.Colon[58]&rectum[59] 288004.Pancreas[60] 147005.NonHodgkin’slymphoma[61] 14500 MEN1.Lung&bronchus 909002.Prostate[62] 370003.Colon&rectum 278004.Pancreas 139005.NonHodgkin’slymphoma 13400
FeelingPain15.Contrarytoanecdotalstories,numerousstudieshavedocumentedthatwomenexperiencepainmoreacutelyandmorefrequentlythanmen,indicatingthatthesexesmaydetectanddampenpaindifferently.Inastudyofdentalpatients,womenrespondedmorefavorablythanmentoaclassofpainrelieversknownaskappaopioids[63],includingpentazocine[64],suggestingthatreceptorsforinhibitingpainmayvarybysex.Moreover,womenarelessresponsivethanmentononsteroidal[65]antiinflammatory[66]drugs,
suchasibuprofen[67].
BoneLoss16.Women,morethanmen,experienceasignificantchangeintheirbonesinlaterlife.In
postmenopausalwomen,theskeletonbecomeslessdense,fullofperforations[68]causedbyosteoporosis.Thereasonforthedifference:lessestrogenaftermenopause.Thehormoneslowsdownbonelossandbuildsupboneaswell.Womenpastmenopausewhohaveestrogenreplacementtherapycanpreventasmuchas75%oftheirbonedegradationandcuttheirriskofahipfracture[69]50%.
Notes
[1]exquisite[5ekskwizit]adj.优 美 的,
高雅的,精致的,剧烈的,异 常 的,细
腻的,敏锐的
[2]marauder[m[5rR:d[]n.掠夺者
[3]accommodate[[5kRm[deit]vt.供应,
供给,使适应,调节,和解,向……提
UNIT06 犎犝犕犃犖犃犖犃犜犗犕犢犃犖犇犘犎犢犛犐犗犔犗犌犢
62
供,容纳,调和
[4]fetus[5fi:t[s]n.胎儿
[5]lupus[5lu:p[s]n.狼疮
[6]rheumatoidarthritis[5ru:m[tRidB:
5Wraitis]n.类风湿关节炎
[7]multiplesclerosis[skli[5r[usis]n.多
发性硬化
[8]estrogen[5estr[dV[n]n.雌激素
[9]rev[rev]v.加快转速
[10]chestcrushingpain胸部压榨式疼痛
[11]hallmark[5hR:lmB:k]n.特点
[12]symptom[5simpt[m]n.症状,征兆
[13]postmenopausal[5p[Jst9men[J5pC:z[l]adj.(妇女)绝经后的,更年期的
[14]tradeoffn.交换,协定,交易,平衡
[15]churn[tF[:n]outv.艰苦地做出
[16]HDL高密度脂蛋白(highdensitylipo
protein)
[17]cholesterol[k[5lest[r[ul]n.胆固醇
[18]erratic[i5rAtik]heartbeats不 规 则 心
跳
[19]hormonereplacementtherapy [5Wer[pi]激素替换治疗
[20]progestin[pr[u5dVestin]n.孕酮,黄
体酮
[21]diagnostic[7dai[g5nRstik]exam诊断
检查
[22]uterus[5ju:t[r[s]n.子宫(= womb)[23]ovary[5[uv[ri]n.[动 物]卵 巢,[植
物]子房
[24]cervix[5s[:viks]n.子宫颈
[25]Papsmearsn.定期进行乳突癌细胞抹
片检查(PapSmearTesting)
[26]malignant[m[5lign[nt]adj.恶性的
[27]cervical[5s[:vik[l]cancer子宫颈癌
[28]uterine[5ju:t[rain]adj.子宫的
[29]orthopedist[9R:W[u5pi:dist]n.整
形外科医师
[30]ligament[5li[m[nt]n.韧带
[31]tear[ti[]拉伤
[32]anteriorcrusiateligament[An5ti[ri[
5kru:sieit5li[m[nt]前十字韧带
[33]thigh[Wai]n.大腿,股
[34]feeltheeffects感到微醉
[35]aspirin[5Asp[rin]n.阿 斯 匹 林(解 热
镇痛药),乙酰水杨酸
[36]platelet[5peitlit]n.血小板
[37]betablockern.β受体阻滞药
[38]migraine[5maigrein]painn.偏头痛
[39]tricyclicantidepressant [trai5saiklik
7Antidi5pres[nt]三环类抗忧郁剂
[40]contraceptive[7kRntr[5septiv]adj.避孕的n.避孕品,避孕用具
[41]Pilln.避孕药
[42]serotonin[7si[r[5t[unin]n.5羟色胺
[43]norepinephrine[5nC:7repi5nefrin]n.去 甲 肾 上 腺 素 (epinephrine[7epi5nefrin]肾上腺素)
[44]adrenalgland[E5dri:nlglAnd]n.肾
上腺
[45]staveoff[steiv]v.避开,挡开,延迟
[46]dementia[di5menFi[]n.痴呆 (如senile[5si:nail]dementia老年性痴呆)
[47]testisterone[5testist[r[un]n.睾丸酮
[48]estradiol[7estr[5dai[ul]n.雌二醇
[49]amputation[7Ampju5teiF[n]n.切除,
切断手术
[50]chemotherapy[7kem[u5Wer[pi]n.化学疗法
[51]osteoporosis[7Rsti[upR:5r[Usis]n.骨质疏松症
[52]tamoxifen[t[5mRksifen]n.[药]三苯
氧胺,它莫西芬(一种抗雌激素,用于治
疗妇女乳腺癌或不育症)[53 ] chronic constipation [5krcnik
7kRnsti5peiF[n]n.慢性便秘
[54]discrepancy[dis5krep[nsi]n.差异
[55]saliva[s[5laiv[]n.口水,唾液
63
[56]setthestagefor:为……打 好 基 础;
为……创造条件
[57]bronchus[5brRNk[s]n.支气管
[58]colon[k[u5l[u]colonsn.结肠
[59]rectum[5rekt[m]n.直肠
[60]pancreas[5pANkri[s]n.胰腺
[61]NonHodgkin’slymphoma[lim5f[um[]非霍奇金淋巴瘤
[62]prostate[5prCsteit]n.前列腺
[63]opioid[5[UpjRid]n.鸦片类物
[64]pentazocine[pen5tAz[si:n]n.[药]戊
唑辛,镇痛新(代替吗啡的合成镇痛药,
不易上瘾)[65]nonsteroidal[nRn5sti[rRid]adj.非
类固醇的
[66] antiinflammatory drug [5Antiin5flAm[t[ridrQg]n.抗炎药
[67]ibuprofen[9aibjJ5pr[Jfin]n.[药]异
丁苯丙酸,布洛芬(抗炎、镇痛药)[68]perforation[p…f[5reiF[n]n.穿孔
[69]hipfracture[hip5frAktF[]n.臀部骨
折
64
犝犖犐犜07 犕犐犆犚犗犅犈犛
犈狊狊犪狔21 犃犵狉狅犫犪犮狋犲狉犻狌犿狋狌犿犲犳犪犮犻犲狀狊犪狀犱犐狋狊犝狊犲狊犻狀犘犾犪狀狋犅狉犲犲犱犻狀犵
1.Agrobacteriumtumefaciens[1]causescrowngall[2]diseaseofawiderangeofdicotyledonous(broadleaved)plants,especiallymembersoftherosefamily[3]suchasapple,
pear,peach,cherry,almond,raspberry[4]androses.Aseparatestrain[5],termedbiovar[6]3,causescrowngallofgrapevine[7].
2.Thediseasegainsitsnamefromthelargetumourlikeswellings(galls)thattypicallyoccuratthecrownoftheplant,justabovesoillevel.Althoughitreducesthemarketability[8]ofnurserystock[9],itusuallydoesnotcauseseriousdamagetoolderplants.Nevertheless,thisdiseaseisoneofthemostwidelyknown,becauseofitsremarkablebiology.Basically,thebacteriumtransferspartofitsDNAtotheplant,andthisDNAintegrates[10]intotheplant’sgenome,causingtheproductionoftumoursandassociatedchangesinplantmetabolism.
3.TheuniquemodeofactionofA.tumefacienshasenabledthisbacteriumtobeusedasatoolinplantbreeding.Anydesiredgenes,suchasinsecticidaltoxingenesorherbicideresistancegenes,canbeengineeredintothebacterialDNAandtherebyinsertedintothe
plantgenome.TheuseofAgrobacterium notonlyshortenstheconventionalplantbreedingprocess,butalsoallowsentirelynew(nonplant)genestobeengineeredintocrops.
4.ThestoryofAgrobacteriumgoesevenfurtherthanthis,makingitoneofthemostinterestingandsignificantbacteriafordetailedstudy.Forexample,thereisahighlyeffectivebiologicalcontrolsystemforthisdisease—oneofthefirstandmostsuccessfulexamplesofbiologicalcontrolofplantdisease.
5.Hereweconsiderthreemajoraspectsofthisintriguing[11]disease:thebiologyofthebacteriumandtheinfectionprocess,thedevelopmentofahighlysuccessfulbiologicalcontrolsystemagainstcrowngalldisease,thewideruseofA.tumefaciensasatoolforgeneticengineeringofplants.
Thebacteriumanditsplasmids6.A.tumefaciensisaGramnegative[12],nonsporing,motile,rodshapedbacterium,
closelyrelatedtoRhizobium[13]whichformsnitrogenfixingnodules[14]onclover[15]andotherleguminous[16]plants.StrainsofAgrobacteriumareclassifiedinthreebiovars
65
basedontheirutilizationofdifferentcarbohydratesandotherbiochemicaltests.ThedifferencesbetweenbiovarsaredeterminedbygenesonthesinglecircleofchromosomalDNA.Biovardifferencesarenotparticularlyrelevanttothepathogenicity[17]ofA.tumefaciens,exceptinonerespect:biovar3isfoundworldwideasthepathogenofgrapevines.Butthisisalmostcertainlybecausebiovar3hasbeenspreadaroundtheworldinvegetativecuttings[18]ofvines,notbynaturalmechanisms.
7.MostofthegenesinvolvedincrowngalldiseasearenotborneonthechromosomeofA.tumefaciensbutonalargeplasmid,termedtheTi(tumourinducing)plasmid[19].Inthesameway,mostofthegenesthatenableRhizobiumstrainstoproducenitrogenfixingnodulesarecontainedonalargeplasmidtermedtheSym (symbiotic[20])plasmid.Thus,thecharacteristicbiologyofthesetwobacteriaisafunctionmainlyoftheirplasmids,notofthebacterialchromosome.(AplasmidisacircleofDNAseparatefromthechromosome,capableofreplicatingindependentlyinthecellandofbeingtransferredfromonebacterialcelltoanotherbyconjugation[21].Plasmidsencodenonessential[22]
functions,inthesensethatabacteriumcangrownormallyincultureeveniftheplasmidislost.)
8.Thecentralroleofplasmidsinthesebacteriacanbeshowneasilyby“curing”[23]ofstrains.Ifthebacteriumisgrownnearitsmaximumtemperature(about30℃inthecaseofAgrobacteriumorRhizobium)thentheplasmidislostandpathogenicity(ofAgrobacterium)ornoduleformingability(ofRhizobium)alsoislost.However,lossoftheplasmiddoesnotaffectbacterialgrowthinculture—theplasmidfreestrainsareentirelyfunctionalbacteria.
9.InlaboratoryconditionsitisalsopossibletocureAgrobacteriumorRhizobiumandthenintroducetheplasmidoftheotherorganism.IntroductionoftheTiplasmidintoRhizobiumcausesthistoformgalls;introductionoftheSymplasmidintoAgrobacteriumcausesittoformnodulelikestructures,althoughtheyarenotfullyfunctional.
10.Studiessuchastheseraisemanyinterestingandchallengingquestionsaboutthenatureofbacteria.Forexample,whatdoesthenameofabacterialspeciesorgenus[24]reallymean,iftheorganismcanchangesodrasticallybylossorgainofanonessentialplasmid?Andhowmuchgeneexchangeoccursbymeansofplasmidsandothermobilegeneticelements[25]withinnaturalpopulations?
Theinfectionprocess11.Agrobacteriumtumefaciensisfoundcommonlyonandaroundrootsurfaces—there
giontermedtherhizosphere[26]— whereitseemstosurvivebyusingnutrientsthatleakfromtheroottissues.Butitinfectsonlythroughwoundsites,eithernaturallyoccurringorcausedbytransplantingofseedlingsandnurserystock.Thisrequirementforwoundscanbedemonstratedeasilyinlaboratoryconditions.Forexample,tothebasesoftwoyoungtomatoplants,adropofA.tumefaciensbacterialsuspensionwasplacedonthestemandapinprick[27]wasthenmadeintothestematthispoint.Fiveweekslater,the
UNIT07 犕犐犆犚犗犅犈犛
66
younggallsdevelopedfromthemeristematic[28]tissuesaroundthecentralvascularsystem.
12.Innaturalconditions,themotilecellsofA.tumefaciensareattractedtowoundsitesbychemotaxis[29].Thisispartlyaresponsetothereleaseofsugarsandothercommonrootcomponents,anditisfoundeveninplasmidcuredstrains.However,strainsthatcontaintheTiplasmidrespondevenmorestrongly,becausetheyrecognizewoundphenolic[30]compoundssuchasacetosyringone[31]whicharestronglyattractiveatevenverylowconcentrations(10-7Molar).Thus,oneofthefunctionsoftheTiplasmidistocodeforadditional,specificchemotacticreceptors[32]thatareinsertedinthebacterialmembraneandenablethebacteriumtorecognizewoundsites.
13.Acetosyringoneplaysafurtherroleintheinfectionprocess,becauseathigherconcentrations(about10-5to10-4 Molar)thanthosethatcausechemotaxisitactivates[33]thevirulencegenes[34](Virgenes)ontheTiplasmid.Thesegenescoordinatetheinfectionprocessand,inparticular:leadtotheproductionofproteins(permeases[35])thatareinsertedinthebacterialcellmembraneforuptakeofcompounds(opines[36])thatwillbeproducedbythetumours;causetheproductionofanendonuclease[37]—arestrictionenzyme[38]—thatexcisespartoftheTiplasmidtermedtheTDNA(transferredDNA).
14.TheexcisedTDNAisreleasedbythebacteriumandenterstheplantcells,whereitintegratesintotheplantchromosomesanddictates[39]thefunctioningofthosecells.Theactualmechanismoftransferisstillunclear,butitseemstorequireaconditioningprocess[40],perhapsmediated[41]bytheproductionofcytokinins[42](planthormones)bythebacterium.Thetzs(transzeatin[43])geneontheTiplasmidcodesforthehormone.
Notes
[1 ] Agrobacterium tumefaciens[9AgrEbAk5ti[ri[m 9tju:
mi5feiF[ns]n.根癌农杆菌
[2]crowngall[kraUngC:l]n.冠瘿病
[3]rosefamilyn.蔷薇科
[4]strain[strein]n.菌株
[5]raspberry[5rB:zb[ri]n.悬钩子
[6]biovar[bai5[uvB:]n.生物型
[7]grapevine[5greipvain]n.葡萄藤,葡萄
树
[8]marketabilityn.可销售性
[9]nurserystockn.苗木,定植苗,出圃
苗
[10]integratev.整合
[11]intriguingadj.迷人的,有迷惑力的,引起兴趣(或好奇心)的
[12]Gramnegativeadj.革兰氏阴性的
[13]Rhizobiumn.根瘤菌
[14]nodule[5nRdjU:l]n.小结,小瘤
[15]clover[5kl[Uv[]n.三叶草,苜蓿
[16]leguminous[le5gju:min[s]adj.豆科的
[17]pathogenicity[7pAW[dVi5nisiti]n.病原性,致病性
[18]vegetative[5vedVit[tiv]cuttingn.营
养切条
[19]Ti(tumourinducing)plasmid[5plAzmid]n.肿瘤诱导质粒
[20]symbiotic[7simbai5Ctik]adj.共生的
67
[21]conjugation[9kCndVu5geiF[n]n.结
合
[22]essential[i5senF[l]adj.必需的
[23]curev.治 愈,治 疗,此 处 指“质 粒 消
除”[24]genus[5dVi:n[s]n.(生物分类)属[25]mobilegeneticelementn.可 移 动 遗 传
因子(转座子)[26]rhizosphere[5raiz[9sfi[]n.根围(指
围绕植物根系在土壤中的一个区域)[27]pinprick针刺
[28]meristematic[7merist[5mAtik]adj.分生组织的
[29]chemotaxis[9kem[5tAksis]n.[动
物]化学 向 性,[生 物]趋 化 现 象,趋 药
性
[30]phenolic[fi5nClik]adj.酚类的
[31]acetosyringone[eisit[u5si[riNgC:n]
n.乙酰丁香酮
[32]chemotactic[9kem[u5tAktik]receptorn.向化性受体
[33]activate[5Aktiveit]v.激活
[34]virulence[5vrul[ns]genen.毒 力 基
因
[35]permease[5p…mieis]n.透过酶
[36]opine[[u5pain]冠瘿碱
[37]endonuclease[7end[5nju:kli7eis]n.内切酶
[38]restrictionenzymen.限 制 性 内 切 酶,限制酶
[39]dictatev.指令,指示,命令,规定
[40]conditioningprocessn.条件作用过程
[41]mediate[5mi:diit]v.作 为 引 起……的媒介,介导
[42]cytokinin[5sait[5kinin]n.细 胞 分 裂
素
[43]tzs(transzeatin)[trAns5zi:[tin]n.反式玉米素
犈狊狊犪狔22 犅犪犮犻犾犾狌狊狋犺狌狉犻狀犵犻犲狀狊犻狊犪狀犱犐狋狊犝狊犲狊
1.Bacillusthuringiensis[1](commonlyknownasBt)isaninsecticidal[2]bacterium,marketedworldwideforcontrolofmanyimportantplantpests— mainlycaterpillarsoftheLepidoptera[3](butterfliesandmoths)butalsomosquitolarvae[4],andsimuliidblackflies[5]thatvector[6]riverblindnessinAfrica.Btproductsrepresentabout1%ofthetotal‘agrochemical’market(fungicides[7],herbicides[8]andinsecticides[9])acrosstheworld.ThecommercialBtproductsarepowderscontainingamixtureofdriedsporesandtoxincrystals.Theyareappliedtoleavesorotherenvironmentswheretheinsectlarvaefeed.Thetoxingeneshavealsobeengeneticallyengineeredintoseveralcropplants.Themethodofuse,modeofaction,andhostrange[10]ofthisbiocontrola
gent[11]differmarkedlyfromthoseofBacilluspopilliae[12].
Modeofaction2.Thecrystalsareaggregates[13]ofalargeprotein(about130~140kDa[14])thatisactuallyaprotoxin[15]—itmustbeactivatedbeforeithasanyeffect.Thecrystalproteinishighlyinsolubleinnormalconditions,soitisentirelysafetohumans,higheranimalsandmostinsects.However,itissolubilizedinreducingconditionsofhighpH(abovea
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boutpH9.5)—theconditionscommonlyfoundinthemidgut[16]oflepidopteranlarvae.Forthisreason,Btisahighlyspecificinsecticidalagent.
3.Onceithasbeensolubilizedintheinsectgut,theprotoxiniscleavedbyagutprotease[17]toproduceanactivetoxinofabout60kD.Thistoxinistermeddeltaendotoxin[18].Itbindstothemidgutepithelialcells[19],creatingporesinthecellmembranesandleadingtoequilibrationofions.Asaresult,thegutisrapidlyimmobilized[20],theepithelialcellslyse[21],thelarvastopsfeeding,andthegutpHisloweredbyequilibrationwiththebloodpH.ThislowerpHenablesthebacterialsporestogerminate,andthebacteriumcantheninvadethehost,causingalethalsepticaemia[22].
4.Recentstudiesonthedeltaendotoxinstructureshowthatithasthreedomains[23].DomainIisabundleof7alphahelices,someorallofwhichcaninsertintothegutcellmembrane,creatingaporethroughwhichionscanpassfreely.DomainIIconsistsofthreeantiparallelbetasheets[24],similartotheantigenbindingregions[25]ofimmuno
globulins[26],suggestingthatthisdomainbindstoreceptorsinthegut.DomainIIIisatightlypackedbetasandwich[27]whichisthoughttoprotecttheexposedend(Cterminus[28])oftheactivetoxin,preventingfurthercleavagebygutproteases.Interestingly,
thediphtheriatoxin[29](ofanotherbacterium)hasanessentiallysimilarstructuretotheBttoxin.
History,productsandinsecthostrange5.Bacillusthuringiensiswasfirstdiscoveredin1911asapathogenofflourmoths[30]fromtheprovinceofThuringia[31],Germany.ItwasfirstusedasacommercialinsecticideinFrancein1938,andthenintheUSAinthe1950s.However,theseearlyproductswerereplacedbymoreeffectiveonesinthe1960s,whenvarioushighlypathogenicstrainswerediscoveredwithparticularactivityagainstdifferenttypesofinsect.
6.Formanyyears,Btwasavailableonlyforcontroloflepidoptera,usingahighlypotent[32]strain(B.thuringiensisvarkurstaki[33]).ThisstrainstillformsthebasisofmanyBtformulations[34].Furtherscreening[35]ofalargenumberofotherBtstrainsrevealedsomethatareactiveagainstlarvaeofcoleopteran[36](beetles)ordiptera[37](smallflies,mosquitoes).Mostofthesestrainshavethesamebasictoxinstructure,butdifferininsecthostrange,perhapsbecauseofdifferentdegreesofbindingaffinitytothetoxinreceptorsintheinsectgut.Forexample,thetoxinsproducedbyB.thuringiensisvaraizawai[38]havesomewhatdifferenttoxinsfromthoseofBt.varkurstakiandtheyarehighlyspecifictolepidoptera,withnoeffectonotherinsects.ThemanycommercialstrainsforcontroloflepidopteraaremarketedundervarioustradenamessuchasBiobit?,Dipel?,Javelin?,etc.
7.Incontrast,thetoxinsproducedbystrainsofB.t.varisraelensis[39]arehighlyactiveagainstsimuliidblackfly,vectorsofsometropicaldiseases,andalsoagainstfungusgnat[40]larvaeandsometypesofmosquito(especiallyAedes[41]species,buthighertoxindosesareneededforcontrolofCulexspp[42].andAnophelesspp[43].).Tradenamesfor
69
theseproductsincludeSkeetal?,Vectobac?andMosquitoAttack?.8.StrainsofB.t.varsandiego[44]orB.t.vartenebrionis[45]aremarketedforcontrolofsomecoleoptera—especiallyforcontroloftheimportantColoradopotatobeetle[46].
Bttoxinsandtheirclassification9.B.thuringiensisstrainsproducetwotypesoftoxin.ThemaintypesaretheCry(crystal)toxins[47],encodedbydifferentcrygenes,andthisishowdifferenttypesofBtareclassified.ThesecondtypesaretheCyt(cytolytic)toxins[48],whichcanaugment[49]
theCrytoxins,enhancingtheeffectivenessofinsectcontrol.Over50ofthegenesthatencodetheCrytoxinshavenowbeensequencedandenablethetoxinstobeassignedtomorethan15groupsonthebasisofsequencesimilarities[50].Thetablebelowshowsthestateofsuchaclassificationin1995,butanalternativeclassificationhasrecentlybeenproposed.
Gene Crystalshape Proteinsize(kDa) Insectactivity
cryⅠ[severalsubgroups:
A(a),A(b),A(c),B,C,D,E,F,G]bipyramidal[51] 130~138 lepidopteralarvae
cryⅡ [subgroupsA,B,C] cuboidal[52] 69~71 lepidopteraanddiptera
cryⅢ [subgroupsA,B,C] flat/irregular 73~74 coleoptera
cryⅣ [subgroupsA,B,C,D] bipyramidal 73~134 diptera
cryⅤ~Ⅸ various 35~129 various
Recentapproachestostraindevelopment10.Ithasbeenknownsincethe1980sthattheCrytoxinsareencodedbygenesonplasmids
ofB.thuringiensis.Therecanbe5or6differentplasmidsinasingleBtstrain,andtheseplasmidscanencodedifferenttoxingenes.TheplasmidscanbeexchangedbetweenBtstrainsbyaconjugationlikeprocess,sothereisapotentiallywidevarietyofstrainswithdifferentcombinationsofCrytoxins.Inadditiontothis,Btcontainstransposons[53](transposablegeneticelementsthatflank[54]genesandthatcanbeexcisedfromonepartofthegenomeandinsertedelsewhere).AllthesepropertiesincreasethevarietyoftoxinsproducednaturallybyBtstrains,andprovidethebasisforcommercialcompaniestocreategeneticallyengineeredstrainswithnoveltoxincombinations.OneofthefirstsuchproductswasaBtstrainmarketedasRaven?forenhancedcontrolofColoradopotatobeetleaswellasforcaterpillarsthatattackpotato,tomatoandauber
gine[55]plants(allofwhichareinthesameplantfamily— Solanaceae[56]).ThisBtstraincontainedtwodifferentbeetleactiveCryIIIproteins(withdifferentbindingaffinitiesformidgutcellmembranesofColoradobeetle)aswellastwocaterpillaractiveCryIproteins.Suchanapproach—oftentermedgenepyramiding[57]—isdesignedtodelaythedevelopmentofresistanceintargetpests,becauseresistancewouldhavetode
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velopsimultaneouslytoseveraldifferenttoxins.11.Suchresistancecandevelopquiterapidlywhenonlyonetypeoftoxinisinvolved.Infact,ithappenedwithin1or2yearswhenthemosquitoactiveBtstrainswerewidelyusedintropicalcountries.Thebasisofresistanceseemstobecomplex,involvingseveralfactors.Butoneencouraging[58]findingisthat,atleastinsomeinsects,thereceptorfortheBttoxinisanessentialgutenzyme,anaminopeptidase[59],soanychangeinthisreceptorthatcausesalossofbindingtothetoxincouldalsobedetrimentaltotheinsect,
potentiallyreducingthefitnessoftheresistantinsects.
PlantsgeneticallyengineeredwiththeBtgene12.Since1996,awiderangeofcropplantshavebeengeneticallyengineeredtocontainthe
deltaendotoxingenefromBacillusthuringiensis.These“Btcrops”arenowavailablecommerciallyintheUSA.Theyinclude“Btcorn”,“Btpotato”,“Btcotton”and“Btsoybean”.SuchplantshavebeengeneticallyengineeredtoexpresspartoftheactiveCrytoxinintheirtissues,sotheykillinsectsthatfeedonthecrops.
13.Insomerespects,thisisanimportanttechnologicalandpracticaldevelopment,becauseitensuresthatonlythoseinsectsthatattackthecropwillbeexposedtoBttoxins—
thereisnorisktoothertypesofinsect.ItalsoensuresthattherangeofusesforBtisextendedtoinsectsthatfeedontherootsorthatbore[60]intotheplanttissues—forexample,theEuropeancornborer[61]— becausesuchinsectscannotbecontrolledbyBtsuspensionssprayedontoplantsurfaces.
14.However,thereisalsoa“downside[62]”,becausethetargetinsectsareperpetuallyexposedtotoxinsandthiscreatesaverystrongselectionpressure[63]forthedevelopmentofresistancetothetoxins.Variouscropmanagementstrategiesarebeingdevelopedtotrytominimizethisrisk.
Notes
[1]B.thuringiensis(Bt)[b[5sil[sWjJ[rindVinsis]n.苏云金杆菌
[2]insecticidal[in9sekti5said[l]adj.杀
昆虫的,杀昆虫剂的
[3]lepidoptera[9lepi5dCpt[r[]n.鳞 翅
目
[4]mosquitolarvae[m[s5ki:t[u5lB:v[]
n.蚊子幼虫
[5]simuliid[si5mju:lid]blackfly蚋黑蝇
[6]vector[5vekt[]v.向……带菌
[7]fungicide[5fQndVisaid]n.杀真菌剂
[8]herbicide[5h[:bisaid]n.除草剂
[9]insecticide[in9sekti5said]n.杀 昆 虫
剂
[10]biocontrolagentn.生物防治剂
[11]hostrangen.宿主范围
[12]Bacilluspopilliaen.(日本)金龟子芽
孢杆菌
[13]aggregate[5Agrigeit]n.聚合体
[14]kDan.(分 子 量 单 位)千 道 尔 顿(kilodalton)
[15]protoxin[pr[u5tRksin]n.原毒素
71
[16]midgutn.(昆虫)中肠
[17]protease[5pr[utieis]n.蛋白酶
[18]deltaendotoxin[7end[u5tRksin]n.德耳塔内毒素
[19]epithelial[7epi5Wi:lj[l]celln.上皮细
胞
[20]immobilize[i5m[Jbilaiz]v.固定
[21]lyse[lais]v.细胞裂解
[22]septicaemia[septi5kAmi[]n.败血病
[23]domain[d[u5mein]n.结构域
[24]betasheetn.beta(折叠)片层
[25]antigenbindingregionn.抗原结合区
[26 ] immunoglobulin [i5mju: n[U5glCbjulin]n.免 疫 球 蛋 白(即 抗
体)[27]betasandwichn.beta(折 叠)片 层 构
成的夹心
[28]Cterminusn.C末端,羧基末端
[29]diphtheria[dif5Wi[ri[]toxinn.白 喉
毒素
[30]flourmothn.面粉蛾
[31]Thuringia[WjJ[rindVi[]n.图林根州
[德意志联邦共和国州名][32]potent[5p[Ut[nt]adj.强力的,有力
的,有效的
[33]B.thuringiensisvarkurstaki苏 云 金
杆菌库斯塔变种
[34]formulation[7fC:mju:leiF[n]n.配
方
[35]screen[skri:n]v.筛选
[36]coleopteran[7kCli5Rpt[r[n]n.鞘 翅
类
[37]diptera[dip5t[r[]n.双翅类
[38]B.thuringiensisvaraizawai苏 云 金
杆菌鲇泽变种
[39]B.t.varisraelensis苏云金杆菌以色列
变种
[40]gnat[nAt]n.小 昆 虫。fungusgnats(蕈蚊):小 型 双 翅 蝇 构 成 蕈 蚊 科 和 尖
眼蕈蚊科任何一种,具有取食真菌的幼
虫。[41]Aedes[ei5idi:z]n.伊 蚊(一 种 传 染 黄
热病的蚊子)[42]Culexspp.[5kju:lek5sQbspi:Fi:z]
库蚊亚种 (常见于北美、欧洲)[43]Anophelesspp.[E5nCfili:z5sQbspi:
Fi:z]按蚊亚种
[44]B.t.varsandiegon.苏云金杆菌圣地
牙哥变种
[45]B.t.vartenebrionisn.苏 云 金 芽 孢 杆
菌拟步行甲变种
[46]Coloradopotatobeetlen.科罗拉多薯
虫
[47]Cry(crystal)toxinn.晶体毒素
[48]Cyt(cytolytic)toxinn.细胞裂解毒素
[49]augment[C:g5ment]v.增加,增大
[50]sequencesimilarityn.序列相似性
[51]bipyramidal[7bai5pir[mid[l]adj.双
棱锥的
[52]cuboidal[kju:5bCid[l]adj.立方形的
[53]transposon[trAns5p[usRn]n.转 座
子
[54]flankvt.在……的侧面,侧翼包围,守
侧面
[55]aubergine[7[ub[5Vi:n]n.茄子,(茄
子般的)紫红色
[56]Solanaceaen.茄科
[57]genepyramidingn.基因聚合。就是将
分散在不 同 品 种 中 的 优 良 性 状 基 因 通
过杂交、回 交、复 合 杂 交 等 手 段 聚 合 到
同一个品种中。[58]encouragingadj.令人鼓舞的
[59]aminopeptidase[[7min[5peptideis]n.氨基肽酶
[60]bore[bR:]v.钻
[61]Europeancornborern.欧洲玉米钻心
虫
[62]downsiden.底侧,下降趋势
[63]selectionpressuren.选择压力
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犈狊狊犪狔23 犛狅犿犲犉犪犮狋狊犃犫狅狌狋犈.犮狅犾犻
WhatdoesthetermE.colimean?
1.E.coli[1]istheabbreviationforthebacteriumintheFamilyEnterobacteriaceae[2]namedEscherichia(Genus)coli(Species)[3].Approximately0.1%ofthetotalbacteriawithinanadult’sintestines(onaWesterndiet)isrepresentedbyE.coli.Butanewborninfant’sintestineshaveE.coli,alongwithlactobacilli[4]andenterococci[5]asthemostabundantbacterialflora[6].2.Itisforthisreasonthattheorganismswhichhappilyinhabittheintestinaltractasnormalfloraarenamedenteric[7]bacteria.TheFamilytowhichE.colibelongs(Enterobacteriaceae)
isnamedwhatitis—becauseoftheGreekwordenterikos—whichpertainstotheintestineandthenameofthepersonwhofirstisolatedandcharacterizedthisbacterium,Escherich.
AreE.colibacteriaSAFE?
3.Yes,mostly.ThepresenceofE.coliandotherkindsofbacteriawithinourintestinesisnecessaryforustodevelopandoperateproperly,andforustoremainhealthy—E.coli,alongwithotherspeciesofbacteria,providesuswithmanynecessaryvitamins.Bacteriamakethevitamins,andweabsorbthem.WedependuponE.coliinourintestinesasoursourceofVitaminKandBcomplexvitamins.4.Thefetusofanyanimaliscompletelysterile.Immediatelyafterbirth,thenewbornsacquireallkindsofdifferentbacteriawhichlivesymbioticallywiththenewbornsandthroughouttheirlife.Fromthedayweareborn,wehavebacteria.Thehelpfulbacteriaarelocated“only”inregionsofourbodydirectlyexposedtotheenvironment(ourintestines,upperandlowerrespiratorytract[8],etc)andneverinourbloodstreamortheinsidetissuesourbody.Animalsthatarebornandraised“germfree”[9]arereallyquiteunhealthy,theyhavethinintestinalwalls,puny[10]hearts,andrequirelotsofvitaminsupplementstoexist.
WhenareE.colibacteriaNOTSAFE?
5.Somebacteriaarenotverynice.WecallsuchindividualE.colibacteriaadifferent“strain”ofbacteriawithinagivenspecies.Someofthesedifferentstrains(andtheremaybeseveralwithinagivenspecies)canbeharmfultous.TheseindividualstrainsofE.coliexist!ThismeansthatthisparticularindividualstrainofE.coliisgeneticallydifferentthanthevastmajorityofE.coliinourintestines.IfthisE.colistrainhappenstohavegeneticinformationforproducingharmfulbyproducttous,weareintrouble.
WhichE.coliareBAD?
6.TherarestrainofE.colithatisBADforusisE.coliO157:H7,amemberoftheEHEC
73
—enterohemorrhagic[11]E.coligroup.ThetermEnterohemorrhagicmeansanintestinallyrelatedorganismwhichcauseshemorrhaging[12],i.e.,lossofblood.
Howdowepickupthisstrain?
7.E.colibacteriaareeverywhereintheenvironment.Theyareacommonoccupantofallanimals.Anytimeweeatsomething,drinksomething,ortouchourhandstosomethingthathasbeeneitherapartoforhasbeennearwhereanimalsare,thereisalwaysthepotentialtoingestthesebacteria.
WheredoesthisstrainofE.colicomefrom?
8.Bacterialcellsareallovertheplaceanditispossibleforthemtoacquiregeneticinformationfromothersources(bacterialviruses,plasmids,orfrompiecesofDNA).Insomecases,acquisitionofthisinformationmayprovideanadvantageforsurvival.ButE.coliO157:
H7appearstohavebeeninfectedwithabacterialvirusthathadtheabilitytoinsertitsownDNAintothebacteria’schromosomewithoutharmingthebacterium.Everytimethisbacterialcelldivided,thevirusDNA,beingnowapartofthebacterialDNA,waspassedontoeverydaughtercell—creatingtheE.colistrain,O157:H7.Thisvirus’sgeneticinformation(genes)containedinformationfortheproductionofatoxin,calledShigaliketoxin(SLT)[13],sometimescalled,Verotoxin.Consequently,thisstrainofE.coli,andallofitsprogenyproducedthistoxin.Thistoxinisaproteinwhichcausesseveredamagetointestinalepithelialcells.Welosewaterandsalts;bloodvesselsaredamagedandbleedingoccurs—
hemorrhaging,aconditionparticularlydangeroustosmallchildren—evenlethal.Childrenaretoosmalltotolerateverymuchbloodandfluidloss.Forthisreason,smallchildrenshouldnotbeallowedtobecomedehydrated,eveninmildcasesofdiarrhea[14].Insomecases,anothersyndromeisinvolvedwhichiscalledhemolyticuremicsyndrome(HUS)[15],
characterizedbykidneyfailureandlossofredbloodcells.Approximately5%to10% ofsmallchildrenprogresstothisstageofthedisease—whichisextremelydangeroustothem.Inseverecases,permanentkidneydamageoccurs.Thisbacteriumcanalsobeverydangeroustotheelderlyorinfirm[16].TherecanbeacombinationofHUSandotherthingswhichinvolvethebloodsystem.Thiscanbelethaltotheelderlyin50%ofthecases.
Notes
[1]E.coli[i5k[ulai]n.大肠杆菌
[2]Enterobacteriaceae[7ent[r[u5bAkti[rieisi[]n.肠细菌科
[3]Escherichia(Genus)coli(Species)埃
希氏菌属大肠杆菌
[4]lactobacillus[7lAkt[ub[5sil[s]n.乳
酸杆 菌;lactobacilli(pl)[7lAkt[ub[si5lai]
[5]enterococcus[7ent[r[u5kRk[s]n.肠
球 菌;enterococci (pl) [7ent [r
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[u5kRsai][6]bacterialflora[bAk5ti[ri[l5flR:r[]
n.细菌群
[7]enteric[en5terik]bacterian.肠细菌
[8]upperandlowerrespiratory[ris5pai[r[t[ri]tractn.上、下呼吸道
[9]germfreeadj.无菌的;adv.无菌
[10]puny[5pju:ni]adj.小 的,弱 的,微
不足道的
[11]enterohemorrhagic [7ent[r[u5hem
[ridVik]adj.肠出血的
[12]hemorrhage[5hem[ridV]n.出血
[13]Shigaliketoxin(SLT)类 志 贺 毒 素
(有时称Vero毒素)[14]diarrhea[7dai[5ri[]n.痢疾,腹泻
[15]hemolyticuremicsyndrome (HUS)[hi:m[u5litik5jur[mik5sindr[um]n.溶血性尿毒症
[16]theinfirmn.体弱多病者
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犝犖犐犜08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
犈狊狊犪狔24 犜犺犲犈犾犲狆犺犪狀狋
1.Everythingabouttheelephantisspectacular.Gestation[1]inthefemaleelephanttakesnearlytwentyonemonths.AmaleAfricanelephantcanweighasseventonsandstandelevenfeetattheshoulder.Althoughtheaverageisless,theIndianspecieshasbeenknowntoreachsixtonsandstandnearlytenfeet.Yetinspiteoftheirsize,bothcanmoveassilentlyasashadowontheirgreatcushioned[2]feetwhentheyneedto.Althoughelephantscansometimesbeverynoisyanimals,tearingdownleavesfromtreesorsquealing[3]whentheyareafraid,theyhaveanalmostfrighteningabilitytodisap
pear.2.Nothingcouldbetterillustratethecontradictionsofnaturethanthefactthatforallthe
powerandstrengthofitsgiantsize,theelephantcannotrunintherealsenseoftheword,asforexampleahorsedoes.Normallyitmovesataboutsixmilesanhour,whilewhenitcharges[4](torushasifinanattack)itdoessoatprobablynomorethantwentymilesanhour,althoughbecauseofitssizeanditsobviousangerachargingelephantisanexperiencenoteasilytobeforgotten.Again,theelephantcannotjump;itcanonlystepacoupleofyardsatatime,whichmakescompletelyeffectivetheapparentlyrathersmallelephanttrenches[5]sometimesdugtoprotecthouses.
3.Asforthosespectaculartusks[6],whichhavesooftenbeenthecurseoftheelephant,
thoseoftheAfricanmaleareoftenmorethansixfeetinlength,lessinthefemale.TheheaviesttuskeverrecordedinAfricaweighed225pounds,whilethegreatestlengthwasnearlyelevenfeetsixinches.
4.InthemaleIndianelephant,tusksarerarelymorethanthreeorfourfeetinlength,
whilethefemaleIndianelephanthasnotusks.AconsiderablenumberofIndianmalesarealsotuskless.Theyareknownas makhnas,beingcompensatedbyimmensestrengthparticularlyinthehead,neckandtrunk[7],anditisquitecommonforatusklessmaletocontrolaherd.
5.Wheretheyexist,thosegreattuskscanbeusedformanypurposes,bothastoolsandweapons.Theycanbeusedtodigupdeliciousrootsormovebranchestoclearthewayforthetrunk.Andwhenthereisnobranchnearby,anelephantwillrestitstrunkononeofitstusks.
6.Itusedtobethoughtimpossibletodomesticate[8]theAfricanelephant,butthisisnot
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so,considerablenumbersbeingtrainedforworkintheonetimeBelgianCongo,nowZaire[9].However,itiswithIndiaandnearbyAsiancountriessuchasBurmaandThailandthatelephantsasforestworkersareusuallyassociated.
7.ThemostcommonmethodofcaptureinIndiaistheancientpittrap[10].Thedisadvantagesofthisarethepossibilityofotheranimals,suchastheIndianbuffalo[11],beingcaught,andalsothepossibilityofanelephantsufferinginjurywhenfallingintothepit,
eventhoughthisneedbeonlyafewfeetdeepowingtotheelephantsinabilitytojumporstepmorethanacoupleofpaces.Butwhatevertheadvantagesordisadvantagesofpitfalltraps,theirconstruction,locationandthewaytheyarehiddenareexcellentexamplesoftheskillandknowledgeofthehunters.InCoorg[12]andMysore[13]thetrappingiscarriedoutbyCorubas[14],membersofoneofthevanishingtribesofIndia.Nowelephants,intheirsearchforfoodandwater,travelgreatdistances,manymiles,alongtheirownspecialtrailsorroads,manydaysorweekssometimespassingbeforetheycomethesamewayagain.AtcarefullyconsideredplacestheCorubasdigtheirpits,
coveringthemoverwithbranchesandleavesandgrassinsuchawaythatunlessoneknowsoftheirexistenceitisimpossibletodistinguishthemformthesurroundingearth.
8.Theidealcaptureisayoungelephantofaroundnineortenyearsofage,becauseitismucheasiertotrain.Bringingacaptivetothesurfaceisasurprisinglysimpleprocess.Afterithasbeentiedwithropetoacoupleofcampelephants[15](withathirdinreserve)standingclosetothepit,thetribesmenbegintofillthepitwithbranchescutfromthesurroundingjungle.Initsangerthecaptivetramples[16]allthisdown,withtheresultthatitisslowlyraisedtogroundlevel.
9.Althoughatfirstsightitwillprobablybeveryviolentanddifficulttohandle,afterthreeweeksitwillbetakingitsfirstlessons,andintimeitwillbeabletodoeverythingtheothercampelephantscando.Itisstrangethatthelargestandmostspectacularlandanimalshouldbesuchanobedientservanttoacreatureitcouldkillwithaslightmovementofitstrunk.
Notes
[1]gestation[dVes5teiF[n]n.怀 孕,孕
育时期,酝酿
[2]cushioned[5kuF[nd]adj.有 软 垫 子
的
[3]squeal[skwi:l]v.长声尖叫
[4]charge[tFB:dV]v.冲锋
[5]trench[trentF]n.深沟,壕沟,战壕
[6]tusk[tQsk]n.象牙
[7]trunkn.象鼻
[8]domesticate[d[5mestikkeiit]vt.驯
养,使安于土地,教化
[9]Zaire[z[5i:r[]n.扎伊尔
[10]pittrapn.坑陷
[11]buffalo[5bQf[l[u]n.(印 度、非 洲 等
的)水牛
[12]Coorg[5ku[g]n.库格(印度一旧省)
77
[13]Mysore[5maisR[]n.迈索尔(印度南
部一城市)[14]Coruba[5kR:r[b[]n.高鲁巴人
[15]campelephantn.象 园 里 训 练 有 素 的
象
[16]trample[5trAmpl]v.践踏,踩坏,轻
视
犈狊狊犪狔25 犔犻狏犻狀犵犜狅犵犲狋犺犲狉
1.Animalsocialsystemsrangefromthetemporarycoupling[1]ofearthwormstothecomplexstructuresofantsocieties,inwhichgroupinterestssoovershadow[2]individualitythattherelationshipofindividualtogroupislikethatbetweencellandorganism.
2.Amongvertebrates,somearemonogamous[3],otherspolygamous[4].Someparentscarefortheiryoung,othersleavethemtofendforthemselves.Someanimalsliveinwanderingherdsorflocksorschools,othersaresolitary[5].Someareterritorial[6],othersnomadic[7].
3.Incertainspecies,thesocialstructurechangeswiththeseason:manybirds,forexample,flocktogether[8]inthefallandwinterbutmaintainindividualterritoriesinthespringandsummer.Somespeciesadjusttheirsocialstructuredependingondifferencesinavailabilityoffoodorshelterandthebehaviorofpreyandpredators[9].Forexample,
anubisbaboons[10],ontheplain,marchinstricthierarchical[11]formation;intheforest,ontheotherhand,theymoveasadisorganizedrabble[12].
4.Animalsocialsystems,itisevident,adapttotheenvironment,asProfessorFrankMckinneyoftheUniversityofMinnesotahasfoundamongducksofthegenusAnas[13].Someducksbreedinpondsrichinfood,soasmallareasuppliesallthefamily’sneeds;
theirsocialsystemaccordinglyconsistsofsmall,exclusivelyheld,vigorouslydefendedterritoriesandmonogamouspairs.Pintails[14],ontheotherhand,livewherefoodiswidelyscattered;territoriallythereforebeinginappropriate,malesoftenstrayandmateatrandomwithanyfemale.
5.Knowledgeofhowananimallivesinnaturecanoftenhelpusunderstanditscommunicationbehavior.Forexample,whethertheanimalusesmainlyvisualorauditorysignalsdependsonhoweasyitistoseeorhearinitshabitat.Furthermore,communicationoperatesonlywithinasocialstructureandthelatterdependsonthenatureofthesignals,
whattheyareusedtoconveyandhowtheyarerespondedto.Forexample,onlyinsocialsystemsthatinvolvepermanentrelationshipsbetweenindividuals(suchasthoseofmatesorofparentsandtheiryoung)istheidentitypartoftheinformationconveyedbysignals.
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
78
Notes
[1]coupling[5kQpliN]n.交配
[2]overshadow[7[uv[5FAd[u]vt.遮蔽,使显得不重要
[3]monogamous[mR5nRg[m[s]adj.单
配偶的
[4]polygamous[pR5lig[m[s]adj.多配偶
的
[5]solitary[5sRlit[ri]adj.独处的
[6]territorial[7teri5tR:ri[l]adj.有 领
土的
[7]nomadic[n[u5mAtik]adj.游牧的
[8]flocktogether聚集在一起
[9]preyandpredator捕食者与猎物
[10]anubisbaboo[[5nju:bis5bB:bu:]n.狒
狒
[11]hierarchical[7hai[5rB:kik[l]adj.分
等级的
[12]rabble[5rAbl]n.乌 合 之 众,下 层 社
会,拨火棍
[13]Anasn.鸭属
[14]Pintail[5pinteil]n.针尾鸭
犈狊狊犪狔26 犆狉犪狕狔犗狑狀犲狉狊犕犪犽犲犳狅狉犆狉犪狕狔犘犲狋狊
1.Thereseemstobeawidespreadbeliefthatifacompanionanimal[1]isbehavinginacrazymanner,thenitisbecausetheownersarecrazyandhavemadehimthatway.Asyoumightexpectthisbeliefismostlyheldbypeoplethatdon’thaveproblemanimals.Thisbeliefiswrongonatleasttwocounts.First,itisnotappropriatetousewordslikecrazy,psychotic[2]orneurotic[3]todescribethebehaviorofcompanionanimals.“Crazy”
doesnothaveascientificmeaningandisnotusedinhumanpsychology[4]ormedicine.Thewordspsychoticandneurotichaveveryspecificscientificmeaningsinhumanpsychology,butaren’tappropriatefordescribingproblemsinanimalsbecausetheyaredefinedintermsofhumancommunication.Therearesomesimilaritiesbetweensomehumanbehaviorproblemsandtheproblemsweseeinourpets,butwemustbecarefulnottoassumethatthecausesarethesame.Thesecondreasonthatthisbeliefiswrongisthatmostbehaviorproblemsofcompanionanimalsarenotcausedbytheirowners.Mostbehaviorproblemsthatpeoplecomplainabout,suchasdogsbarking,catsnotusingthelitterbox[5]orevenanimalsbitingpeople,arenormalbehaviorfortheanimal,
buttheyoccursattimesorinplacesthatarenotacceptabletopeople.Theseanimalsarenotcrazy,it’sjustthattheirnormalanimalbehaviorconflictswithourhumanneeds.Admittedly[6],therearesomebehaviorproblemsthatanimalsshowthataretrulyabnormal,butagainwehavelittleevidencethattheownershavecreatedtheabnormalbehavior.Mostoftheanimalsthatweseeinourbehaviorpracticeliveingoodhomeswithcaringandlovingowners.Mostareobediencetrained,getregularveterinary[7]careand
79
arewellcaredfor.Despitethis,theanimalsdeveloptheirbehaviorproblemsanyway.Wedon’tknowwhysomeanimalsdevelopbehaviorproblemsandothersdon’t.Geneticpredispositions[8],earlyexperiencesorotherfactorsallmayplayarole.
2.Sometimesownersmayunknowinglycreatebehaviorproblemsoutofignorance.Apuppy[9]leftinthehouseforeighttotenhoursatatimewillsurelyhousesoil[10],andalongtermeliminationproblem maybecreated.Sometimespeopleunwittingly[11]encouragebehaviorproblems.Encouragingadogtobarkatorchaseadeliveryperson(“WhoisitRover?Gogethim!”)cancreateormakeworseabarkingoranaggressionproblem.Ownersthatcreateormakeworsebehaviorproblemsaretheexception,nottherule.
Notes
[1]companionanimaln.同伴动物
[2]psychotic[sai5kRtik]adj.精 神 病 的
n.精神病患者
[3]neurotic[nju[5rRtik]n.神经病患者
adj.神经质的,神经病的
[4]psychology[sai5kRl[dVi]n.心理学,心理状态
[5]litterbox[5litEbRks]n.垃圾箱
[6]admittedly [[d5mitidli]adv.诚 然,无可否认
[7]abnormal[Ab5nC:m[l]adj.反常的
[8]veterinary[5vet[rin[ri]n.兽医adj.医牲畜的,兽医的
[9]predispositionn.易患病的体质
[10]puppy[5pQpi]n.(常指未满一岁的)小狗,小动物,自负的青年
[11]housesoil[5haussRil]vi.弄脏屋
[12]unwittingly[Qn5witiNli]adv.不知情
地,无意地
犈狊狊犪狔27 犉犻狊犺犪狀犱犛狅狌狀犱
1.Fishalsocommunicatewithsound.OnespeciesinparticularcausedastirinSausalito,
Californiainthe1980s.Asuccessfulantipollutioncampaign[1]hadclarifiedthewaters
ofthebay,andmadethehouseboats[2]thatlinetheshorenewlyfashionable.Butsud
denlyresidentsbeganlosingsleepbecauseofaloudhum[3]thatappearedtocomefrom
thewater.Someblamedanewlylaidpowerline.Othersthoughtthesewage[4]workshadsecretlyresumedpumpingatnight.Butthecausewas,inasense,theclearwater.
2.Cleaningupthebayhadproducedaperfectenvironmentfortoadfish[5],aslimy[6],bi
zarre[7]lookingrelativeofsearobins[8],sculpins[9]andmidshipman[10].Itturnsout
thatthetoadfishhumsalovesongtoattractmates.Andmaleshuminchorus[11]duringthebreedingseason,sometimescontinuingforanhour.Thischorusoflovesongshadsparkedtheconcernofhouseboatowners.
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
80
3.Toadfishalsomaketwoothersounds.Grunts[12],warningsthatapparentlytellrivalmalestobackoff[13]orpotentialpredatorstostayaway,lastonlytwotenthsofasecond.Thesocalledboatwhistlelastsnearlyasecond,mayattractfemalesaswellashummingdoes,andmightidentifyindividuals.Inthedistantlyrelatedbicolordamselfish[14],femalescandistinguishindividualmalechirps[15]andmalescantellthechirpoftheirnearestneighborfromthevocalizations[16]ofmoredistantmales.Fishsoundsfunctionmainlyinmateattraction[17],butarealsousedinschoolcoordination[18],andtheytravelwellunderwater.Scientistshaveobservedfishrespondingtoasoundsignalfromhalfamileaway.
4.Fishproducesoundsinavarietyofways,oftenwithorgansmuchlessspecializedforthetaskthanthevocalapparatusofothervertebrates.Gruntsappeartocomefrom
grindingteeth[19],thesoundamplifiedbytheairfilledswimbladder[20].Andspecialmusclesinorneartheswimbladderitselfcancauseittovibratelikeadrumhead[21].
5.Neurobiologist[22]AndrewH.Bass,ofCornellUniversity,hasstudiedsoundproductioninthemidshipman,sometimescalledthesingingfish[23].Asetofspecialdrummingmuscles[24]attachtothewallsofthemidshipman’sheartshapedswimbladder.AsBassexpected,females— whodon’tsing—havesmallerswimbladdersandsmallerdrummingmuscles.ButBassfoundasurprise.Somemalessport[25]femalesizedswimbladdersandweakdrummingmuscles.Furthermore,thesemalesresemblefemalesinbodysizeandshape.These“midshipwimps[26],”whomakeuplessthan10percentofBass’sstudypopulation—don’tsingorbuildnests,andtheirsimilaritytofemalescontinuesallthewaytotheanatomyandcellularstructureoftheirbrains.Butdon’tlettheirnonmasculinebuild[27]foolyou.Theymateandpassongenesquitesuccessfully.
6.Thesmallmidshipmanmalesemployastrategyseeninmanyfishandinotheranimalsaswell.Theyaresocalledsatelliteorsneakermales[28].Themajorityofmalesfollowtheusualroute,eatandgrowtoalarge,attractivesize,competeforspace,buildand
guardanestandgruntyourheartout.Theyreaptherewardofanestfullofeggslaidbyseveralfemales.Butsneakermalesslinkaroundtheedgesofterritories,slippingintodepositsperm(sneakspawning[29])whilenormalmalesarebusyguardingandshowingoff.Theirspermdonotfertilizemanyeggsinasinglenest,buttheycansneakspawninseveral.Inasecondslystrategy,somesmallmalesreleasetheirmilt[30]intothewatersurroundinganestandfanthespermladenwatertowardthenestwiththeirfins.
7.Fishhear—orfeel—soundintwoways.Somehavesmallbonesconnectingtheinnerear[31]totheswimbladder,creatingineffectasinglelargeear.Fishhavenoouterears[32],andthereforenoneedforthemiddleearbones[33]thatconnecttheeardrum[34]
totheinnerear.Buttheydopossessaninnerearsimilartothoseofothervertebrates.8.Butfishalsodetectvibrationsinthewaterwithauniquelaterallinesystem[35]similarinmanywaystoourinnerears.Whereorganofhearinginourinnerearsformsacoil,thatoffishliesstretchedoutalongitsside.Thelaterallinetubestretchesthelengthofa
81
fish,andsometimesbranchesarounditshead.Thetubeconnectstothewaterbywayofsmallporesintheskinandscales.Mucus[36]fillsthetube,justasinourcochlea[37].Whenapressurewavestrikesthefish,itjiggles[38]themucusandbendssmallhairsthatprojectintothemucusinbunches[39].Thehairstriggernerveimpulses[40],whichtraveltothebrain.Whilefishcannotdeterminethelocationofasounddetectedthroughthesingleswimbladder,theycanlocatesoundsdetectedbywayofthelateralline.
Notes
[1]antipollutioncampaign[5Antip[5lju:
F[nkAm5pein]n.抗污染运动
[2]houseboat[5haJsbaJt]n.形如房子的
船,游艇
[3]hum [hQm]v.嗡 嗡 叫,哼n.嗡 嗡
声,嘈杂声
[4]sewage[5sju:idV]n.下水道,污水
[5]toadfish[5t[JdfiF]n.蟾鱼,豹蟾鱼
[6]slimy[5slaimi]adj.黏 糊 糊 的,(分
泌)黏液的,泥泞的
[7]bizarre[bi5zB:]adj.奇异的(指态度、
容貌、款式等)[8]robin[5rRbin]n.知更鸟
[9]sculpin[5skQlpin]n.大 头 鱼,杜 父
鱼(一种杜父鱼科的海生或淡水 鱼,具
有巨大的扁平头和突出的脊柱),饭桶
[10]midshipman[5midFipm[n]n.海军学
校 学 生,英 国 海 军 少 尉 之 候 补 军 官;
蟾鱼(一种 蟾 鱼 属 的 蟾 鱼,在 其 身 侧 有
几排发光器官)[11]chorus[5kC:r[s]n.合 唱,合 唱 队,
齐声
[12]grunt[grQnt]vi.(猪 等)作 呼 噜 声,(表示烦恼、反对、疲劳、轻蔑等)发哼声
vt.咕哝着说出n.呼噜声,咕哝
[13]backoffv.后退
[14] bicolor damselfish [5bai7kQl [
5dAmzel7fiF]n.双色小热带鱼
[15]chirp[tF[:p]n.喳 喳 声,唧 唧 声v.吱喳而鸣,尖声地说
[16]vocalization[9v[Jk[lai5zeiF[n]n.发
声法
[17]mateattractionn.伴侣吸引
[18]schoolcoordination [sku:lk[u7C:
di5neiF[n]n.群体协调
[19]grindingteethn.磨牙
[20]swimbladder[5blAd[]n.浮囊,鱼鳔
[21]drumhead[5drQmhed]n.耳鼓
[22]neurobiologist [9nju:[r[u5baiRl[dVist]n.神经生物学家
[23]singingfishn.唱歌鱼
[24]drummingmusclen.振动肌
[25]sportvt.炫耀,夸示
[26]midshipwimpn.懦弱蟾鱼 (此处是作
者造 的 一 个 词,与 midshipman相 关,
wimp意为“懦弱的”)[27]nonmasculinebuild[nJn5mB:skjulin
bild]n.非阳性身体
[28]satelliteorsneakermalen.卫星雄性,
偷偷摸摸的雄性
[29]sneakspawn[spR:n]n.偷偷产卵
[30]milt[milt]n.(充满精液的)雄鱼生殖
腺,(雄鱼的)精液,鱼白
[31]innerearn.内耳
[32]outerearn.外耳
[33]middleearbonen.中耳骨
[34]eardrum[5i[drQm]n.耳膜
[35]lateral[5lAt[r[l]linesystemn.侧线
系统
[36]mucus[5mju:k[s]n.黏液
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
82
[37]cochlea[5kRkli[]n.耳蜗
[38]jiggle[5dVigl]v.(使)轻 摇,(使)微
动n.轻摇,微动
[39]bunch[bQntF]n.串,束v.捆成一束
[40]nerveimpulse[5impQls]n.神经脉冲
犈狊狊犪狔28 犃狀犻犿犪犾狊’犝狊犲狊狅犳犆狉狔犻狀犵犪狀犱犅犲犵犵犻狀犵
1.Throughouttheanimalkingdom,helplessoffspring[1]havewaysofdemandingattentionthatparentscan’tignore.Butalltheyelling[2]andscreaming[3]andpeeping[4]andbleating[5]maycommunicatemuchmorethanmerehungerandthirst.
2.Fromahatchling[6]magpie[7]’sfirsttentative[8]squawk[9]toanewbornbaby’scry,thecaresoliciting[10]signalsofdependentoffspringarethefirstformofcommunicationinmanyspecies.Theyarealsoamongthemostostentatious[11]formsofcommunicationaround.Writhing[12]broods[13]ofsongbirds[14],necksoutstretchedandbeaksagape[15],
confrontparentsatthenest.Chinstrappenguin[16]siblingschasetheirparentsthroughcrowdedrookeries[17]forameal.Robinchicks,jockeying[18]forpreferredfeedinglocationsinthenest,getintoshoving[19]matches.Evenbeforehatching,whenheatandnotfoodistheresourcechickscrave[20],embryonicwhitepelicans[21]vocalize[22]intheegg.Nor[23]arethesedisplayslimitedtobirdsandmammals.TadpolesofthepoisonousfrogDendrobatespumilio[24]performvigorousswimdisplayswhentheirmotherscheckonthem,andmotherfrogsoftenrespondbyleavingbehindunfertilizedeggsasfood.Eveninsectlarvaetrytogetadultattention.Immatureburyingbeetles[25]gesticulate[26]attheirparentstoearnahelpingofregurgitated[27],rottenmeat.
3.Indeed,mostoffspringdisplaysseemmuchmoreextravagantthanonewouldthinknecessarytoelicitattentionfromparentsalreadyeagertoprotectandfeedtheirown.Surelynaturalselectiondesignedmaternalbrainstoberesponsive.Theexcitedsquealsofhungrypiglets[28]andthebleatsofinsistentlambsseembetterdesignedforpestering[29]
reluctantmothersthanforconveyingasimplemessageofneed.Whyhasn’tevolutionprogrammedhumanbabiestoseekparentalfavorwithpleasantsoundsandgestures—anudge[30],forexample,orahushed[31]whimper[32]?
Notes
[1]offspring[5RfspriN]n.(单 复 数 同
形)儿女,子孙,后代,产物
[2]yell[yel]vi.大叫,忍不住笑,呼喊
[3]screaming[5skri:miN]adj.尖叫的,令人惊愕的,引人捧腹大笑的
[4]peep[pi:p]vi.窥视,偷看
[5]bleat[bli:t]vi.羊叫声,咩咩,咩咩叫
[6]hatchling[5hAtFliN]n.人 工 孵 化 的
鱼苗或小鸟
[7]magpie[5mAgpai]n.鹊
83
[8]tentative[5tent[tiv]adj.试验性的,试探的,尝试的,暂定的
[9]squawk[skwR:k]v.发 出 叫 声,诉
苦,抗议n.粗粝的叫声
[10]solicit[s[5lisit]v.恳求
[11]ostentatious[7Rsten5teiF[s]adj.卖
弄的,装饰表面的
[12]writhe[raiT]v.翻腾,局促不安
[13]brood[bru:d]n.(动 物 中 鸟 或 家 禽
的)一窝,(同种或同类的)一伙
[14]songbirdn.鸣禽,鸣鸟,女歌手
[15]agape[E5geip]adv.张口发呆地,目
瞪口呆地
[16] chinstrap penguin [5tFinstrAp5peNgwin]n.帽带企鹅
[17]rookery[5rukk[ri]n.群 居 地,穴,白
嘴鸦的群居地,海豹等之穴,破旧而拥
挤的住房群,贫民窟
[18]jockey[5dVRki]v.谋求n.职业赛马
骑师,(机器的)操作员
[19]shove[FQv]vt.[口]推挤,猛推,强
使vi.推
[20]crave[kreiv]v.恳求,渴望
[21]pelican[5pelik[n]n.鹈鹕
[22]vocalize[5v[uk[laiz]v.发声
[23]nor[nC:]conj.也不
[24]Dendrobatespumilion.草莓箭毒蛙
[25]buryingbeetle[5beriiN5bi:tl]n.埋
葬虫
[26]gesticulate[dVes5tikjUleit]v.做 姿
势表达,用手势谈话
[27]regurgitate[ri5g[:dViteit]v.(使)涌
回,(使)流回,(使)反刍
[28]piglet[5piglit]n.小猪
[29]pester[5pest[]vt.使烦恼,纠缠
[30]nudge[nQdV]n.用肘轻推,轻推为引
起注意
[31]hush[hQF]v.使安静或沉默n.安静
[32]whimper[5wimp[]vi.呜咽,哀诉,呜
咽的说
犈狊狊犪狔29 犉狉狅犵犆犪犾犾狊
1.Asduskfallsoveraswampy[1]pond,thechorusbegins.Firstonefrogcroaks[2],alittle
hesitantly.Soonanotherjoinsin.Suddenlythepondresonates[3]withthevoicesofdozensofmalefrogs,eachsignalinghisspecies,availabilityandqualificationsasafather.Twopopulationsofthesamespecies,separatedgeographically—ahighwayrunningthroughaswamp,forexample—developdialects,slightdifferencesintheircalls.Inmostspecies,onlymalescall,thoughthefemalemidwifetoad[4]outshouts[5]hermate.Asuddenforeignsoundsilencesthemoneandall.Butsoonasinglevoicestartsagain,
followedbyanotherandanother.2.Thesoundofapondfulloffrogscanreachdeafeninglevels,faroutofproportiontothetinybodiesproducingthesound.Anairsac[6]onthefloorofthefrog’smouthenablesit
todotworemarkablethings.First,whenit’sexpanded,thesacactsasaresonator[7],
likethehollowbodyofaviolin.Second,byforcingairintothesacfromthelungs,thenbackintothelungs,afrogcancroakcontinuously,evenunderwater.Theloudestfrogsbreedintemporaryponds.Whenthewater’savailable,themalesmuster[8] mates
quickly,forallfrogslayeggsonlyinwater,andthetadpolesmustgrowlegsbeforethe
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
84
temporarypondsdryup.3.Butforsheercacophony[9],theyearroundsingingoftropicalfrogsbeatsall.Inthetropicalrainforest,oneoftherichestecosystemsonearth,aswamphousesmanyfrogspecies.Maleswouldgainnothingbyattractingandattemptingtomatewithfemalesofanotherspecies,sotheyhavetomaketheirsignalscutthroughthedin[10].
4.ThemaleLeptodactylusocellatus[11],whichlivesinSouthAmerica,callsatabout250to500Hz(roughlyanoctave[12],frommiddleC[13]toabovemiddleC[14]).Hisvolumeisnomatch,however,foraneighboringspecies,whichoverlapshisfrequencyrangeandcancroak40decibelslouder.That’slikethedifferencebetweenaconversationaltoneandthenoiseonafactoryfloor.L.ocellatus,however,hasevolvedawaytocircumvent[15]thispotentialproblem —bycroakingunderwater.
5.Becausesoundtravelswellunderwater,butdoesn’tcrosstheinterfaceintotheair,L.ocellatusavoidssoniccompetitionwithoutchanginghispreferredoctave.Inarichenvironment,speciesdividetheenvironmentupintotinierandtinierslices,eachbecomingaspecialist.Singingunderwaterrepresentsanextrememethodofdividingthe“airwaves[16]”.Mostfrogscroakdistinctivelybyvaryingthepitch[17]oftheircalls,orbyvar
yingthepatternofcroaksinasong.Evenwhentheycandistinguishthecallofmalesoftheirownspecies,though,femalefrogsmustdeterminethedirectionfrom whichitcomes.Thispresentsaproblem.
6.Humansandothermammalscandeterminethedirectionofasoundbecausetheirbrainsdetectdifferencesinloudnessandtimeofarrivalateachoftheirtwoears.Forthissystemtowork,thewavelengthofthesoundmustbemuchsmallerthanthedistancebetweenthetwoears.Thelongerthewavelength,theharderitistotellwherethesoundcamefrom.Thecrest[18]ofalongsoundwavemayhitthenearearonlyatinyfractionofasecondbeforeithitsthefarear.Acomparativelylongtimelater,thenextcrestreachestheears.Thisiswhysomestereosystemscontainonlyasinglelowfrequencywoofer[19],whichthelistenercanplaceanywhereintheroom.Bycontrast,thehighfrequencytweeters[20]andmidrangespeakers[21]mustbeseparatedandproperlyplacedtogivethestereoillusion[22]ofanorchestra[23]intheroom.
7.Humanshearonlyupto20000Hz,andthehighestnoteonthepianoisonlyalittleabove4000Hz.Butmanymammalshearextremelyhighfrequencies,upto60000Hz,
quitewell.Thesesoundwavesaremuchshorterthaneventhetiniestmammalheads.Frogs’highfrequencyhearingisnotassharp.Theytopoutat10,000Hz,makingthedistancebetweentheireardrumstooshorttolocalizethehighestpitchestheyhear.Sohowdofemalesfindtheirmate?Scientistsstudyingthecoquifrog[24]ofPuertoRico[25],
Eleutherodactyluscoqui[26],thinktheyhavealead.8.Onewayfrogscanlocalizesoundisbyhearingasoundtwiceinthesameear.Becauseofthefrog’sheadanatomy,soundcantravelfromthemiddleeardowntheEustachiantube[27],acrossthefrog’smouthcavity[28],uptheotherear’sEustachiantubeandintothemiddleear.Soundcanthenaffectthenearearofafrog,forexample,twice.First
85
whenthesoundstrikestheeardrum,andsecondwhenitarrivesabitlaterbywayofthemouthandEustachiantubesfromthefarear.Thesetwosoundsmayarriveoutofphase[29],withpeaksandtroughs[30]interactinginawaythatgivesthefrog’sbrainaclueastowherethesoundcamefrom.Thispathwaydoesn’taffectmammalsbecauseourmouthandearanatomydifferfromthatoffrogs.
9.Bymappingvibrationinthefrog’sbodywithlasers,thescientistshavefoundthataparticularspotoverthelungsofsomespeciesvibratesaswellastheeardrum.Theyproposethatthebodywallhereactslikealargeeardrum,providingyetanotherpathwayforsoundtotraveltotheeardrum —fromlungtomouthtoEustachiantubetomiddleear.Thismayfurtherincreasetheprecisionwithwhichfemalefrogsfindtheirprinces.
Notes
[1]swampy[5swRmpi]adj.沼 地 的,多
沼泽的,潮湿的
[2]croak[kr[uk]n.蛙或鸦的叫声
[3]resonate[5rez[neit]v.(使)共 鸣,(使)共振
[4]midwifetoadn.产 婆 蟾(雄 蟾 以 后 脚
带着卵的方式保护卵,故名)[5]outshout[7aUt5FaUt]vt.叫 得 比
……响
[6]airsac[sAk]n.气囊
[7]resonator[5rez[neit[]n.共振器,共
鸣器
[8]muster[5mQst[]v.集 合,召 集,征
召,鼓起(勇气等),集聚
[9]cacophony[kA5kCf[ni]n.刺 耳 的 音
调,不谐和音,杂音
[10]dinn.喧嚣
[11]Leptodactylusocellatusn.眼 斑 细 趾
蟾
[12]octave[5Ckteiv]n.八个一组的物品,八度音阶
[13]middleCn.(音)中央C,中央C音
[14]abovemiddleC高中央C音,超高音
[15]circumvent[7s[:k[m5vent]vt.围绕,包围,智取
[16]airwaven.电视,广播的频道
[17]pitch[pitF]n.音调
[18]crest[krest]n.波峰
[19]woofer[5wUf[]n.低音用扩音器
[20]tweeter[5twi:t[]n.高音喇叭
[21]midrangespeakern.中音喇叭
[22]stereoillusion[5sti[ri[Ui5lU:V[n]
n.立体感觉
[23]orchestra[5C:kistr[]n.管 弦 乐 队,乐队演奏处
[24]coqui[5k[Ukwi]frogn.科奎蛙
[25]PuertoRico[5pw[:tou5ri:k[n]n.波多黎各(拉丁美洲)
[26]Eleutherodactyluscoqui多米尼加树蛙
[27]Eustachian[ju:s5teiFi[n]tuben.耳
咽管
[28]mouthcavityn.口腔
[29]outofphaseadv.异相地,不协调地
[30]trough[5trC:f]n.波谷
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
86
犈狊狊犪狔30 犇狅犾狆犺犻狀狊
1.Amongnonhumananimals,birdstakefirstplaceinimitating[1]sounds,includinghumanwords.Butperhapssurprisingly,marinemammalsplacearespectablesecond[2].Certainharborseals[3]havelearnedtobarkout(barely)recognizablewords,andwhalesimitateeachotherduringthedevelopmentoflong,complexsongs.Butthemostwidelystudiedmarinemammalvocalizersaredolphins[4].
2.Dolphinscommunicatewithagreatnumberofdifferentsounds,fromtherepetitiveclicks[5]usedforecholocation[6](andpossiblytocommunicate)towhistlesandgrunts;
incaptivity,theycanimitatehumanwordstosomeextent.Theirecholocationappearstrulyremarkable.Ablindfoldeddolphincanfindanobjectthesizeofapennyonthebottomofaswimmingpoolandcandistinguishsmallobjectsbasedontheirshapeandthematerialthey’remadeof.Butmoreremarkable,perhaps,arethevocalizationsmoreobviouslyusedforcommunication.
3.Whistlesatfirstappeartosayonesimplething:“Hi!I’mFlipper.”Researchsincethe1960shasindicatedthatdolphinseachhaveauniquewhistle,calledasignaturewhistle[7].Thisimpliesdolphinscanproduceseveraldifferentwhistles—atleast10to25,
thenumberofindividualsinanaveragesizedgroup.Furthermore,theymustlearnthesignaturewhistlesofeveryotherdolphininthegroup.Reviewsofthewhistlesofmorethan100dolphinssuggesttheydonotchooseasignaturefromafixedsetofwhistles,
butdevelopanindividualwhistle.Asthedolphinmatures,itssignaturebecomessomewhatstereotyped[8].Toidentifyindividualsbytheirwhistles,dolphinsmustalsohavethementalabilitytolinktheindividualwhistlewithanindividualdolphin.Thisseemslikely,judgingfromexperimentsteachingdolphinstolinkhumanhandsignals,humanwhistlesandevenelectronicallygeneratedsoundstoparticularobjects(forexample,
imitatingthetuneto“MaryHadaLittleLamb”whenshownaFrisbee[9]).4.Behaviorists[10]PeterTyackofStanfordUniversityandLaelaSayighoftheUniversityofNorthCarolinaatWilmingtonstudiedapopulationofwilddolphinsnearSarasota,Florida.Thesedolphins,agroupstudiedfordecadesbyRandalWellsoftheChicagoZoologicalSociety,remaininonearea,soresearcherscanrepeatedlyfindindividuals,
whichtheyrecognizebythedolphins’individualmarkings.Becausetheycan’ttellwhichdolphinismakingaparticularsoundinagroup,theyrecordthedolphinsindividuallyaftercorralling[11]themwithanet.Thetechniqueprovidesonlyaseminatural[12]
environment,buthasyieldedintriguinginformation.5.First,Sayighconfirmedthatindividualdolphinshaverecognizablesignaturewhistles,
andthatthosewhistlesremainstableforatleastadecade.Shealsofoundthatmothersandcalves[13]remaininvocalcontactwhenoneisinthecorralandtheotherswimmingnearby.WhenSayighbeganrecordingnewborncalfwhistles,shefoundafaint,quaver
87
y[14]soundthatvariedfromwhistletowhistle,likethewrittensignatureofayoungchild.Bytheageofone,thecalfhadfirmedupanindividualwhistlethatthenremainedmoreorlessconstantforadecade.
6.Sayighalsofoundmaleandfemalecalvesdevelopwhistlesdifferently.Afemalecalflearnsawhistledistinctlydifferentfromhermother’s.Abrother’swhistle,ontheotherhand,developsfromavariablebabywhistletoanadultformcloselyresemblinghismother’s.Inthispopulationofdolphins,atleast,femaleswithnewborncalveshangoutwiththeirmothers,grandmothersandotherfemales,formingalonglastinggroup.Similarsignaturewhistlesamongayoungfemale,hermother,grandmotherandevenotherfemalescouldleadtoconfusion,likehavingafamilywithtwomemberswiththesamename;thewrongpersonisalwaystakingthetelephonecall.Malecalvesleavethegroupwhentheymature,sotheystandlittlechanceofbeingmisidentified[15].
7.Whilethismodificationofsignaturecallsappearstorelyonlearning,Sayighhasnotruledoutageneticbasis.Forexample,ifthesignaturecallweregenetic,itmightresideonintheXchromosome.AfemalewouldinherittwoXchromosomes,onefromherfatherandonefromhermother.Hersignaturewouldthendifferfromeither.Amale,ontheotherhand,inheritsonlyoneX,fromhismother,andhiscallwouldresemblehers.
8.Studyingsignaturewhistlescanposeproblemsforresearchers.Althoughhumanscanheardolphinwhistlesunderwater,theycannotlocatethesourceofthewhistles.Norcantheylocatethesourceofthewhistlespickedupbyunderwatermicrophonesandbroadcasttopside.Isolatingthedolphinssolvestheproblemofidentifyingwhoissqueaking[16].Butevenwhentwodolphinscancommunicatebywayofasortofunderwaterwalkietalkie[17]—astheycouldinoneexperiment—isolationseverelydisruptssocialcommunication.
9.PeterTyackinventedonesolutiontotheproblem,allowinghimtoreliablyrecordthewhistlesoftwoormoreindividualdolphins.Hecallshisinventionthevocalight[18].ThethreeandahalfinchlongdevicelookslikeacrossbetweenasmallflashlightandamodelofStarTrek’sU.S.S.Enterprise[19].Asuctioncupholdsthedevicetotheslickdolphinskininfrontoftheblowhole.Arowoflightemittingdiodes[20]pointstothefrontandabatterycasetotheback.Inside,amicrophonepicksupthedolphin’ssoundsandelectronicsilluminatethediodesinresponsetothesounds.Thelouderthesounds,themorediodeslightup.
10.Tyackfirststudiedtwodolphins,ScottyandSpray,wholivedinanaquarium[21]calledSealandinBrewster,Massachusetts.Tyacksetupthetwowithvocalights,onewithreddiodesandonewithgreen.Heandotherobserverscalledoutthecolorandnumberofdiodeswhenevertheyheardawhistlepickedupbyanunderwatermicrophone.Ataperecordercapturedboththewhistlesandtheobservers’voices.
11.Bydisplayingthewhistlesassonograms[22],Tyackfoundmorethanthreequartersfellintotwoeasytorecognizecategories.TheType1whistlerises,swoopsdowntoalow
UNIT08 犃犖犐犕犃犔犅犈犎犃犞犐犗犚
88
erpitchedhalfsecondlongwhistle,andthenrisesslightly.TheType2whistlealsorises,fallsandlevelsout,butthenrisesabruptlyattheend.Althoughbothdolphins
producedbothkindsofwhistles,Tyacknoticedindividualvariations.Spray’sType1wasnotidenticaltoScotty’sType1,andtheirType2whistlesdifferedevenmore.Interestingly,thetwodolphinssplittheirwhistlesbetweenthetwotypesdifferently.TwothirdsofSpray’swhistlesfellintotheType1category,whilealmostthreequartersofScotty’swereType2.TyackinterpretstheseresultstomeanthatType1wasSpray’ssignatureandType2Scotty’s.Eachdolphinimitatedtheother’ssignaturewhistlesomeofthetime,Tyackcontends,perhapsusingtheotherdolphin’ssignaturewhistleasalabelorname.
12.Thedolphinsalsowhistledvariationsonthosetwothemes—theyleftpartsout,variedthedurationofthewhistle,changedthepitchslightlyandvariedtheshapeofthesoundsasseenonasonogram.Tyackmaintainsthedolphinscoulddetectthesevariationsandthemanywhistlesthatfellintoneithercategory.
13.Sprayunfortunatelydied,leavingScottyinisolation.Tyackreturnedaftertwoyears,
curioustoseeifScotty’svocalizationshadchanged.ScottynolongerusedSpray’sfavoritewhistleatall.Andhiswhistlesingeneralhadbecomequieterandbriefer,lendingweighttotheideathatdolphinwhistlesfunctionassocialcommunication.
14.Giventhisevidentcomplexity,dolphins’vocabulariesmaywellencompassmuchmorethan“Hi!I’mScotty.”and“Hi!I’mSpray.”
15.Althoughdolphinvocalizationsinthewildmaystretchbeyondmeresignaturewhistles,
pastattemptstoreadimitationofhumansoundsintotheirsqueakyvoicesstandonshak
yground.Eventoday,rapidevaluationoftheirhighpitchedsoundsprovesdifficult.Furthermore,theirsleek,fingerlessflippers[23]makeitdifficultforthemtoproducethekindsofartificialcommunication— handgesturesandkeyboarduse—thatapescanmuster.Butresearchhasmovedaheadontheothersideofcommunication,dolphins’abilitytounderstandlanguage.
16.LouisM.HermanandhiscolleaguesattheKewaloBasinMarineMammalLaboratory,
UniversityofHawaiiatManoa,havetaughtfourwildcaughtdolphinsartificiallangua
ges.Onelanguageconsistsofcomputergenerated,highpitched“words.”Inthesecond,atrainerconveyswordswithhandandarmgestures.Neitherlanguagebearsanyresemblancetohumanlanguageexceptinthatbothcontaingrammaticalrules.Eachlan
guagecomprisesabout40words,nounssuchas“channel,gate,person”and“ball;”
verbssuchas“under”(thegoimplied)and“fetch;”andmodifierssuchas“surface,
bottom,right”and“left.”
17.Usingtheselanguages,Hermancanaskanumberofquestionsaboutdolphins’abilitytocomprehendwordsasreferentstospecificobjectsandtounderstandthattheorderofthewordsmakesadifference.Unlikehumangradeschoolers,thedolphinsneverreceivedanygrammarlessons.Insteadtheylearnedtherulesbyexample.“PhoenixAkeunder,”forexample,meansthetrainerwantsPhoenixtoswimunderAkeakamai(Ake
89
forshort).ThegesturallanguagelearnedbyAkeincludedareversegrammar,topreventwordbywordresponses.Thedolphinreceivingagesturalcommandmustunderstandthefulltwoorthreewordsentencebeforebeginningtorespond.
18.Hermanfoundthatthedolphinslearnedbothwhateachwordreferredtoandhowtointerprettheorderofthewords.Forexample,Akedistinguishedbetweengesturalsentencessuchas“righthoopleftFrisbeefetch”and“lefthooprightFrisbeefetch.”Thefirstsentencemeans“TaketheFrisbeeonyourlefttothehooponyourright.”Successwithsuchsentencesdemonstratesthedolphins’abilitytounderstandboththeseman
tic[24](wordmeaning)andsyntactic[25](sentencepattern)componentsofthelanguage,
Hermanwrites.19.Ake,however,hasgonebeyondmerelyrespondingastrained.Sheeveninventsher
ownlogicalresponsestounusualsituations.Ifatrainercommands“Frisbeehoopin,”atwogesturesequenceaskingAketoputthehoopontopoftheFrisbee,Akenormallycomplies.ButAkehasalsolearnedtouseyesandnopaddles.ForexampleifeithertheFrisbeeorthehoopwereunavailable,thetrainerswouldexpecthertopressthenopaddle.Sometimes,askedtheabovequestionwithbothobjectsinthetank,Akewouldputthehoop—theobjectthecommandaskshertomanipulate—ontheyespaddle,abehaviorsheinvented.IftheFrisbeeisnotinthetank,Akewillputthehoopontheno
paddle.If,ontheotherhand,thehoopismissing,shewillnotmovetheFrisbee—thetrainerdidn’taskherto—butwillpressthenopaddle,meaningshecan’tcomplywiththecommand.
20.Akerespondstonovelcombinationsofwordscorrectly,showingunderstandingofboththewordsandthesequence.Butwhatdoesshedowithaconstructionthatmakesnosense?Akewillmoveanobjecttomakeitpossibletocomplywithacommand.Shewillliftahoopthat’slyingonthebottomofthetanksoshecanswimthroughit,forexam
ple.Ifinsteadsheseesasentencethatgivesanimpossiblecommand,suchas“personwaterfetch,”Akedoesnothing.Shecan’tmovethewatertotheperson.Amorecom
plexkindof“impossible”command,“personwaterhoopfetch,”containstoomanynouns.InthisinstanceAkesensiblyignoresthenounwaterandinterpretsthesentenceas“takethehooptotheperson.”Shehasinterpretedtheimpossible“water”asamistake,muchlikeahumanwillassumeaduplicatedwordrepresentsatypographical[26]error.Hermanseestheseuntaughtresponsesasindicationsthatdolphinsmakeamentalrepresentationofthegrammaticalrulesoftheirartificiallanguage.Byreferringtothismemoryofthestructure,theycanmakesenseofnovelorevennonsensicalsentences.
21.Apictureisworthathousandwords,thesayinggoes.Inthisdigitalage,isapicturecomposedononlyeveryotherpixel[27]worthonlyfivehundred?Onthecontrary,wecanstill“read”apicturewithalargepartofthedigitaldetailmissing,animageofAbrahamLincolnmadeofonlyafewdozenblocksofcolor,forexample.HermanwonderedwhetherPhoenixandAkecould“read”gesturalcommunicationwithreduceddetail.FirsthepresentedavideotapeofatrainertothedolphinsonanunderwaterTV
90
monitor.Theyrespondedalmostaswellastotherealtrainer.Nextheblankedouttheheadandtorso[28],leavingonlythearms,thenremovedthearms,andfinallypresentedonlytwomovingwhitespotstorepresentthehands.Thedolphinsrespondedtoallofthesepresentations,theircorrectresponsesfallingoffonlywiththelast,mostabstractpresentation.Eventhisminimalist[29]communicationelicitedmorecorrectresponsesthanchancewouldpredict.Humantrainers(collegestudents)withfourmonthsofexperienceinthegesturallanguagedidaboutaswell.
22.Fromtheseandotherstudies,Hermanconcludesthatdolphinsusewordsoftheartificiallanguagetorefertoobjectsinanabstractway,andcanmakesenseoftheartificialgrammaraswell.
Notes
[1]imitate[5imiteit]vt.模仿,仿效,仿
制,仿造v.模仿
[2]marinemammalsplacearespectablesecond.海洋 哺 乳 动 物 处 于 可 敬 的 第
二位
[3]harborseal[5hB:b[si:l]n.斑海豹
[4]dolphin[5dClfin]n.海豚
[5]click[klik]v.发出滴答声n.滴 答 声
发出滴答声
[6]echolocation[ek[Jl[J5keiF[n]n.回
声定位能力,回声定位法
[7]signaturewhistle[5signitF[hwisl]n.签名哨
[8]stereotyped[5steri[Jtaipt]adj.套用
老调的
[9]frisbee[5frizbi:]n.飞盘(塑料投掷玩
具)[10]behaviorist[bi5heiv[rist]n.行为主义
者
[11]corral[kR:5rB:l]n.畜栏vt.关进畜
栏
[12]seminatural[9semi5nAtF[r[l]adj.半自然的
[13]calf[kB:f]n.小海豚
[14]quavery[5kweiv[ri]adj.震音的,颤
声的
[15]misidentify[9misai5dentifai]vt.识别
错
[16]squeak[skwi:k]n.尖 叫 声,吱 吱 声
v.发出尖叫声
[17]walkietalkie[5wR:ki5tC:ki]n.无线
电话机
[18]vocalight[5v[uk[5lait]n.红 外 线 声
场系统
[19]StarTrek’sU.S.S.Enterprise星 际
旅行的美国“企业”号船模。[20]diode[5dai[Ud]n.二极管
[21]aquarium [[5kwZ[ri[m]n.养 鱼 池,玻璃缸,水族馆
[22]sonogram[5sCn[7grAm]n.语图
[23]flipper[5flip[]n.鳍状肢
[24]semantic[si5mmAntik]adj.词法的,语义的
[25]syntactic[sin5tAktik]adj.句法的
[26]typographical[7taip[5^rAfik[l]adj.印刷上的,排字上的
[27]pixel[5piks[l]n.像素
[28]torso[5tC:s[u]n.未完成的(不完整
的)作品,残缺不全的东西;躯干
[29]minimalist[5minim[list]n.最低限要
求者,最低纲领主义者
91
犝犖犐犜09 犉犗犗犇,犖犝犜犚犐犜犐犗犖犃犖犇犎犈犃犔犜犎
犈狊狊犪狔31 犉狅狅犱
1.Ithasbeensaidthat“wearewhatweeat”[1],andfromaphysiologicalpointofviewitisthefoodweeatthatbuildsourbodiesandinfluencesourgeneralhealthanddisposition[2].
2.Oneofthesaddestfeaturesofthemodernworldisthatmillionsofpeopleroundthe
globedonothaveenoughtoeatandmanymoredonothavetherightkindsoffoodre
quiredforgoodhealth.Weareconstantlyfacedwith,thestarkcontrast[3]betweennationsinthedevelopedcountrieswhohavemorefoodthantheyneed,andthemillionsinmanydevelopingcountrieswhoarehungryandoftenstarving.
3.Inordertobehealthy,manneedsabalanceddiet[4]containingprotein,fat,carbohydrate[5],vitaminsandminerals[6].Thecarbohydrateinbread,rice,potatoesandsugar
y[7]foodsprovideenergyforthebody.Toomuchcarbohydrate,however,resultsinobesity[8],whichcanendangerhealth.Thefatsandoilsinmilk,cream,butter,cheeseandfatmeat[9]providethebody’smainstoredfoodandcontaintwiceasmuchenergyascarbohydrates.Theproteinincheese,eggs,meat,fishandmilkpromotegrowthandrepairdamagetothebody’stissues.Thebodyalsoneedssmallamountsofvitaminsandminerals.Providedaperson’sdietconsistsofavarietyoffoodssuchasmeat,fish,
eggs,milk,greenvegetablesandfruit,therequiredamountsofvitaminsandmineralsaretakenin.
4.Foodisadailynecessity[10]forlife,butthewayinwhichitispreparedandservedisanintegralpartofeveryculture.Comparethewayinwhichmeat,fish,andvegetablesare
preparedinCantonesecooking[11]withthewaytheyarepreparedinIndian,FrenchofSpanishcooking[12]anditisimmediatelyapparenthowdifferentfoodpreparationisinthevariouscultures.
5.Historically,thedietsofdifferentsocietieshavebeendictatedbysuchfactorsasclimate,soilandtheeaseordifficultyoftransportingfoodsfromoneplacetoanother.ThesimpledietoftheBedouinArab[13],consistingofdates[14],grainandoccasionallymeatandvegetablesresultedfromanaridenvironmentwhichonlyallowedafewfoodstobeproduced.Ontheotherhand,acountry,suchasFranceendowed[15]asitiswithagoodclimateandrichsoil,hasalwayshadanabundanceandgreatvarietyoffoods.Consequently,Frenchcuisine[16]hasdevelopedintooneofthegreatcomplexityandva
UNIT09 犉犗犗犇,犖犝犜犚犐犜犐犗犖犃犖犇犎犈犃犔犜犎
92
riety.6.Thekindsoffoodspeoplebecomeaccustomedtointheearlyformativeyears[17]becomeanintegralpartoftheirpsychologicalmakeup.Iftheymovetoanothercountryandculture,theytendtotaketheireatinghabitswiththemandtoclingtothestyleoffoodtowhichtheyareaccustomed.Itispsychologicallyreassuring[18]toeatthefoodsoneisusedto:thebestwaytomakeaforeignvisitorfeel‘athome’istoofferthemthekindoffoodtheywouldeatintheirowncountry.
7.Whendiscussingfoodanddiet,itisalwaysnecessarytotreattheworld’spopulationastwodistinctsections:thosewhohavefoodinrelativeabundanceandthosewhosuffershortagesofeventhemostbasicfoods.Theinhabitantsofdevelopedcountriesbenefitfromtheirwealthandtheadvancesinfoodtechnology.Refrigeration,foodpreservationandrapidtransportsystemsallowpeopleinBritain,forexample,toenjoyfoodsfromallpartsoftheworld.Unabletogrowsufficientfoodfortheirneeds,theBritishimportawidevarietyoffoods,fromthehumble[19]potatotoexotic[20]tropicalfruits.Foodprocessinghasmeantthattheseasonsnonlongerdictatediet:vegetablessuchaspeasandbeansarecannedorfrozenandareavailablethewholeyearround;softfruitssuchasstrawberries[21]whichareonlyproducedlocallyforashortseason,canbeimportedfromotherpartsoftheworld;citrusfruitsandbananas,whichdonotgrowatallintemperate[22]Britain,arebroughtinfrom Mediterranean[23]andthetropics[24]andarecontinuouslyavailable.
8.Thedevelopedcountriesdo,however,payapenaltyforhavingsuchanabundanceoffood:obesityandtheconcomitant[25]diseasessuchasheartdiseasearemoreprevalent.IthasbeensaidthattheFrench,forexample,whoconsumeaparticularlyrichdiet,
commitsuicidewithaknifeandfork.Butevenintherichcountries,aneconomicrecessioncanaltereatinghabits.Althoughsomedevelopednationshavebecomeslightpoorer,theresulthasnotbeendamagingandmayevenprovetobeagoodthinginthatthepeopleinthesecountrieswilleatalittleless.Theeffectsofeconomicrecessiononmanydevelopingcountries,however,havebeendisastrous,withfamine[26]anddeathsweepingthroughvastareasofAfrica.Althoughdroughtisaprincipalcauseofthisfamine,
theeconomicpressuretoproducecashcrops,suchascotton,forexporthasreducedtheabilityofthesecountriestoproducefoodcropsfortheirownpeople.Alreadysaddled[27]
withhugeforeigndebts,manydevelopingcountriescannotbuythefoodtheyneedfromabroad.Fortunately,thedevelopedcountrieshavereactedtothefaminecrisisandareprovidingfoodaidfromtheirembarrassinglyhighfoodsurpluses.Meanwhile,overlargepartsoftheglobe,hungrypeoplearewonderingnotwhattoeat,butiftheywilleat.
93
Notes
[1]wearewhatweeat食色,性也
[2]disposition[disp[5ziF[n]n.性情
[3]starkcontrastn.鲜明对比
[4]balanceddiet[5dai[t]n.平衡膳食
[5]carbohydrate[5kB:b[U5haidreit]n.碳水化合物
[6]mineral[5min[r[l]n.矿物质
[7]sugary[5FUg[ri]adj.含糖的,甜的
[8]obesity[[u5bisiti]n.肥胖
[9]fatmeatn.肥肉
[10]dailynecessityn.每日必需品
[11]Cantonesecooking[7kAnt[5ni:zkukiN]
n.广东烹饪
[12]Spanishcookingn.西班牙烹饪
[13]Bedouin[5bedUin]Arabn.贝多因人
(一个居无定所的阿拉伯游牧民族)[14]daten.枣子
[15]endow[in5daU]v.捐赠,赋予
[16]cuisine[kwi5zi:n]n.厨房烹调法,烹
饪,烹调风格
[17]formativeyearsn.形成时期
[18]reassuring[9ri:[5FJ[riN]adj.安 心
的,可靠的
[19]humble[5hQmbl]adj.卑下的,微贱
的,谦逊的,粗陋的
[20]exotic[ig5zCtik]adj.异 国 情 调 的,外来的,奇异的
[21]strawberry[5strR:b[ri]n.草莓
[22]temperate[5temp[rit]adj.有 节 制
的,适度的,戒酒的,温带的
[23]Mediterranean[7medit[5reinj[n]n.地中海
[24]tropics[5trRpiiks]n.热带地区
[25]concomitant[k[n5kCmit[nt]adj.随
之而来的
[26]famine[5fAmin]n.饥 荒,[古]饥 饿,严重的缺乏
[27]saddle[5sAdl]v.承受
犈狊狊犪狔32 犞犻狋犪犿犻狀狊
1.Intheearlydaysofseatravel,seamenonlongvoyageslivedexclusively[1]onmeatand
biscuits.Manyofthemdiedofscurvy[2],adiseaseofthebloodwhichcauseswollen
gums[3],livid[4]whitespotsonthefleshandgeneralexhaustion[5],Ononeoccasion,in
1535,anEnglishshiparrivedinNewfoundland[6]withitscrew[7]desperatelyill.The
men’slivesweresavedbyIroquoisIndians[8]whogavethemvegetableleavestoeat.Graduallyitcametoberealizedthatscurvywascausedbysomelackinthesailors’dietandCaptainCook,onhislongvoyagesofdiscoverytoAustraliaandNewZealand,establishedthefactthatscurvycouldbewardedoff[9]bytheprovisionoffreshfruitforthesailors.
2.Nowadaysitisunderstoodthatadietwhichcontainsnothingharmfulmayyetresultinseriousdiseaseifcertainimportantelementsaremissing.Theseelementsarecalled‘vitamins’.Quiteanumberofsuchsubstancesareknownandtheyaregivenletterstoi
UNIT09 犉犗犗犇,犖犝犜犚犐犜犐犗犖犃犖犇犎犈犃犔犜犎
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dentifythem,A,B,C,D,andsoon.Differentdiseasesareassociatedwithdeficienciesofparticularvitamins.EvenaslightlackofVitaminC,forexample,thevitaminmostplentifulinfreshfruitandvegetables,isthoughttoincreasesignificantlyoursusceptibilitytocoldsandinfluenza.
3.Thevitaminsnecessaryforhealthybodyarenormallysuppliedbyagoodmixeddiet,includingavarietyoffruitandgreenvegetables.Itisonlywhenpeopletrytoliveonaveryrestricteddiet,sayduringextendedperiodsofreligiousfasting,orwhentryingtoloseweight,thatitisnecessarytomakespecialprovisiontosupplythemissingvitamins.
4.Anotherexampleofthedangersofarestricteddietmaybeseeninthediseaseknownas“beriberi”[10]whichusedtoafflictlargenumbersofEasternpeopleswholivedmainlyonrice.Intheearlyyearsofthiscentury,aDutch[11]scientistcalledEijkmanwastryingtodiscoverthecauseofberiberi.Atfirsthethoughtthatitwastransmittedbyagerm.HewasworkinginaJapanesehospital,wherethepatientswerefedonricewhichhadhadtheouterhuskremovedfromthegrain.Itwasthoughtthiswouldbeeasierforweak,sickpeopletodigest.Eijikmanthoughthisgermtheorywasconfirmedwhenhenoticedthechickensinthehospitalyard,whichwerefedonscraps[12]fromthepatients’plates,werealsoshowingsignsofthedisease.Hethentriedtoisolatethegermhethoughtwascausingthedisease,buthisexperimentswereinterruptedbyahospitalofficial,whomdecreedthatthehusklesspolishedrice[13],eventhoughleftoverbythepatientswastoogoodforchickens.Itshouldberecookedandthechickensfedoncheap,coarserice[14]withtheoutercoveringstillonthegain.
5.Eijikmannoticedthatthechickensbegantorecoveronthenewdiet.Hebegantoconsiderthepossibilitythateatingunmilledricesomehowpreventedorcuredberiberi,
whilethatalackofsomethinginthepolishedriceorsomeingredientinthehuskmightbethecauseofthedisease.Indeedthiswasthecase.TheelementneededtopreventberiberiwasshortlyafterwardsisolatedfromricehusksandisnowknownasvitaminB1.Themilledrice,thoughmoreexpensive,wasinfactperpetuating[15]thediseasethehospitalwastryingtocure.Nowadays,thisterriblediseaseismuchlesscommonthankstoourknowledgeofvitamins.
Notes
[1]exclusively[ik5sklU:sivli]adv.排外
地,专有地
[2]scurvy[5sk[:vi]adj.下 流 的,卑 鄙
的,无礼的n.[医]坏血病
[3]gum[gQm]n.齿龈
[4]livid[5livid]adj.铅 色 的,(被 打 得)
青紫色的
[5]exhaustion[ig5zR:stF[n]n.耗 尽 枯
竭,疲惫,筋疲力尽,竭尽,详尽无遗
的论述
[6]Newfoundland[7njU:f[nd5lAnd]n.纽芬兰(岛)(加拿大一省)
95
[7]crew[kru:]n.全体船员,(工作)队[8]IroquoisIndian[5ir[kwRi5indj[n]
adj.易洛魁族印第安人
[9]ward[wR:d]offv.避开,挡住
[10]beriberi[5beri5beri]n.脚气病
[11]Dutch[5dQtF]n.荷 兰 人,荷 兰 语
adj.荷兰的
[12]scrap[skrAp]n.碎片,废品堆放场
[13]polished[5pRliFt]ricen.精白米,上
白米
[14]coarsericen.糙米
[15]perpetuate[p[:5petjueit]vt.使永存,使不朽
犈狊狊犪狔33 犉狅狅犱狊犜犺犪狋犉犻犵犺狋犆犪狀犮犲狉
1.Preventionisalwayspreferabletoacure,andwhilemuchofthedataarestillpreliminary[1],agrowingbodyofevidencesuggeststhatthelocalgreenmarket[2]maybearichsourceofanticancer[3]agents.Inparticular,certainfruitsandvegetablesseemtohavepowerfultumorfightingpropertiesthatresearchersarejustbeginningtoappreciate[4]andtostudy.Asamplingofthecurrentcrop[5]offindings:
2.Tomatoes:scientistshavelongknownthatmenwhoeatcookedtomatoproductssuchaspastasauces[6]tendtohavelowerratesofprostatecancer.Untillastweek,however,
thedatawereanythingbutconclusive.Astudyreportedatlastweek’smeetingoftheAmericanAssociationforCancerResearchshowsthatdailydosesoflycopene[7],anantioxidant[8]thatripenstomatoesandgivesthemtheirredcolor,maynotonlypreventprostatecancerbutshrinkexistingtumorsaswell.Menwhotook30mgofthesupplement[9](thequantityfoundin2lbsoftomatoes)hadlowerlevelsofprostatespecificantigen—anindicatorofcellgrowth—andsmallertumors.
3.Soy:previousstudiesshowedthatwomenwhoeatsoyproductssuchastofu[10]andsoymilk[11]arelesslikelytodevelopbreastcancer.Butitwasneverclearwhy.Nowasmallstudyoftwodozenwomenmaypointtoananswer:soyseemstokeepcirculatinglevelsofestrogenlow,whichinturninhibitsbreastcellsfromproliferating.Womeninthestudydrankmorethanfourglassesofsoymilkadayforonemonth,andtheirpeakbloodlevelsofestrogendropped40%.
4.Broccoli[12]:amongallthecancerfightingvegetables,broccoli,cauliflower[13]andcabbagestandsout,especiallyincancersofthebladder[14].Regardlessofhowmanyfruitsandvegetablesagroupof48000menate,onlythoseconsumingbroccoliandrelatedcruciferousveggies[15]reducedtheirriskofbladdercancer,accordingtoareportintheJournaloftheNationalcancerInstitute.Broccolianditskinmayfightcancerbydetoxifyingorganismsinthegutthatwouldotherwisetriggermalignanciesinbladdertissues.
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Notes
[1]preliminary[pri5limin[ri]adj.预 备
的,初步的
[2]greenmarketn.蔬菜市场
[3]anticancer[5Anti5kAns[]adj.抗 癌
的
[4]appreciate[[5pri:Fieit]vt.赏识,鉴
赏,感激vi.增值,涨价
[5]crop[krRp]n.一 些,大 量;农 作 物,产量,平头,短发vt.收割,修剪,种
植vi.收获
[6]pastasauce[5pB:st[sR:s]n.意大利面
酱
[7]lycopene[5laik[7pi:n]n.番茄红素
[8]antioxidant[5Anti5Rksid[nt]n.抗氧化
剂
[9]supplement[5sQplim[nnt]n.补充品
[10]tofu[t[UfU:]n.[日]豆腐
[11]soymilk[sRimilk]n.豆奶
[12]broccoli[5brRk[li]n.花茎甘蓝
[13]cauliflower[5kR:liflau[]n.花椰菜
[14]bladder[5blAd[]n.膀胱,气泡
[15]cruciferousveggie[krU:5sif[r[svedVi]n.十字花科蔬菜
97
犝犖犐犜10 犕犗犔犈犆犝犔犃犚犅犐犗犔犗犌犢犃犖犇犜犚犃犖犛犌犈犖犐犆犛
犈狊狊犪狔34 犜犺犲犘狅犾狔犿犲狉犪狊犲犆犺犪犻狀犚犲犪犮狋犻狅狀(犘犆犚),狋犺犲犅犪狊犻犮狊
1.PolymeraseChainReaction(PCR)[1]isatechniqueforreproducingspecificDNAse
quencesinvitro.Thisprocess,inventedbyKaryMllisin1987,hasbeenautomatedforroutineuseinlaboratoriesworldwide.Theprocessiscarriedoutwithinamachinecalledthermocycler[2],anditcanproducemillionsorbillionsofcopiesofapieceofDNAinafewhours.
2.ThesequenceofPCRinvolvesthefollowingsteps:
A:TheDNAtobereproducedisheatedtoseparatethetwotemplate[3]strands.B:Twoprimers[4]whicharecomplimentarytotheregiontobeamplifiedareadded.C:AheatstableDNApolymeraseenzymeisalsoadded.Theenzymecatalysestheextensionoftheprimers,usingtheDNAstrandastemplate.
D:Thecycleisrepeated,withthenewlysynthesizeddoublestrandedDNAbeingheatdenatured[5]andtheenzymesextendingtheprimersattachedtotheliberatedsingleDNAstrands.
Thechainreaction,oncesetup,resultsintheexponentialamplification[6]oftheoriginalDNA,wherethenumberofcycles(n)determineshowmanycopiesoftheDNA(2n)areproduced.TheamountofamplifiedtargetY=X (1+efficiency)n,whereXistheinputcopynumber[7]andnthenumberofcycles.
3.APCRreactioniscomprisedof:(1)adoublestrandedDNA molecule:thisisthe“template”whichcontainsthese
quencetobeamplified.(2)primer(s):thisisasinglestrandedDNAmoleculewhichcananneal(bind)toaDNAsequenceinthetemplateDNAwhichhasthecomplementarysequence.
(3)dNTPs:amixturewithequalamountsofdATP,dTTP,dGTP,anddCTPwhicharethenucleotidesubunitswhichwillbeputtogethertoformnewDNAmoleculesinthePCRamplificationprocedure.
(4)TaqDNApolymerase[8]:theenzymewhichsynthesizesthenewDNAmoleculesusingthedNTPs.
4.HowPCRcanbeusedtodistinguishbetweentwodifferentDNAsequences?EachPCR
primeranneals[9]onlytoasequenceintheDNAtemplatewhichiscomplementarytoits
own.Ifprimer#1andprimer#2canannealtoGenomeA,thenPCRcanoccuranda
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DNAproductwillbesynthesizedinthePCRreaction.However,ifGenomeBdiffersfromGenomeAinthesequencetowhichprimer#2annealstotheDNA,thenPCRcannotoccursuccessfullyusingGenomeBDNAasatemplate,andnoDNAproductissynthesized.Thus,thispairofprimers(#1and#2)allowsustodistinguishbetweenGenomeAandGenomeB.GenomeAandGenomeBcanrepresentgenomicDNAfromtwoindividualsinthesamespeciesorpossiblyfromtwodifferentspecies.CertainportionsofgenomicDNAtendtoveryconserved[10](verylittlevariation)whileotherportionstendtovarygreatlyamongindividualswithinaspeciesoramongdifferentspecies.
5.ThetrickinsuchPCRanalysisisto:(1)findthosesequenceswhichhavejustenoughvariationtoallowustodetectdifferencesamongtheorganismsthatwearestudying;(2)findtherightPCRprimerswhichwillallowustodetectsequencedifferences.
6.TheapplicationsofPCRareextensive,someare:(1)AmplificationofsmallamountsofDNAforfurtheranalysisbyDNAfingerprinting[11].(2)TheanalysisofancientDNAfromfossils.(3)Mappingthehuman(andotherspecies)genome.(4)Isolationofa
particulargeneofinterest[12]fromatissuesample.(5)Detectionofmicroorganisms
presentinlownumbersinsoil,foodorwater.
Notes
[1]Polymerase[5pRlim[7reis]ChainRe
action(PCR)n.聚 合 酶 链 式 反 应
(PCR)
[2]thermocycler[W[:m[U5saikl[]n.热
循环仪
[3]template[5templit]n.模板
[4]primer[5praim[]n.引物,初级读本,
雷管
[5]denature[di:5neitF[]vt.变性
[6] exponential amplification [7eksp[U5nenF[l7Amplifi5keiF[n]n.指数性
扩增
[7]inputcopynumbern.输入拷贝数
[8]TaqDNApolymerasen.TaqDNA聚
合酶。它是从一种水生栖热菌 (Ther
musaquaticus[W[:m[s[5kwAtik[s])
yT1株中 分 离 提 取 的。yT是 一 种 嗜
热真菌,能在70℃~75℃生长。该菌
是1969年从美国黄石国家森林公园火
山温泉中分离的。
[9]anneal[[5ni:l]n.退火,焖火,锻炼,
磨炼(意志)
[10]conserved[k[n5s[:vd]adj.保守的
[11]fingerprinting[5fiNg[5printiN]n.指
纹作图
[12]geneofinterestn.目的基因
99
犈狊狊犪狔35 犕犲狋犺狅犱狊狅犳犘犾犪狀狋犌犲狀犲犜狉犪狀狊犳犲狉
1.TheDNA(deoxyribonucleicacid)fromdifferentorganismsisessentiallythesame—
simplyasetofinstructionsthatdirectscellstomaketheproteinsthatarethebasisoflife.WhethertheDNAisfromamicroorganism,aplant,ananimalorahuman,itismadefromthesamematerials.
2.Throughouttheyears,researchershavediscoveredhowtotransferaspecificpieceofDNAfromoneorganismtoanother.
3.Aresearcher’sfirststepintransferringDNAisto“cut”orremoveagenesegmentfromachainofDNAusingenzyme“scissors”tocutataspecificsitealongtheDNAstrand.
4.Theresearcherthenusesthese“scissors”tocutanopeningintotheplasmid—theringofDNAoftenfoundinbacteriaoutsideofacell.Next,theresearcher“pastes”orplacesthegenesegment[1]intotheplasmid.Becausethecutendsofboththeplasmidandthegenesegmentarechemically“sticky”[2]theyattachtoeachother,formingaplasmidcontainingthenewgene.Tocompletetheprocess,researchersuseanotherenzymetopasteorsecurethenewgeneinplace.
5.Ourresearcherscontinuetoworkcarefullytoensurethatimprovedcropsarethesameascurrentcrops,exceptfortheadditionofonebeneficialtrait[3]which,forexample,
protectsthemfromaparticularinsectorvirus.6.AtMonsanto,researchersusetwomethodstointroducenewgenes,ortraits,intocrops.
Agrobacteriummethod7.Agrobacteriumisusedinbroadleafed(dicots)cropssuchastomatoes,potatoes,cottonandcanola[4]tointroduceanewgeneintoaplant.Agrobacteriumtumefaciensisasoilmicroorganismthatactsasanaturalgeneticengineer[5].ItcaninsertapieceofitsDNAintothechromosomeofaplantcell.Monsantoresearchersdiscoveredthatforsomekindsofplants,Agrobacteriumwastheperfectmethodforintroducingnewtraitsintotheplant.WhenpiecesofplanttissuewereaddedtoculturewiththeAgrobacteriumcontainingthenewgene,thegenecouldbetransferredintotheplantcells.Thesecellsgrowintoplantswiththenewtrait.
ParticleGun[6]
8.Forsomegrasslike(monocots[7])crops,suchascornandwheat,theAgrobacteriummethoddoesn’twork.Inthesecrops,researchersuseaparticleguntotransfergenes.Inthismethodmicroscopicpellets[8]ofgoldortungsten[9]arebathedintheDNAwiththenewtrait.Thepelletsarefiredfromthegunintotheplantcells.Astheparticlespassthroughthecell,someoftheDNAisleftbehind.TheDNAfromthepelletmixes
UNIT10 犕犗犔犈犆犝犔犃犚犅犐犗犔犗犌犢犃犖犇犜犚犃犖犛犌犈犖犐犆犛
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withtheDNAofthecell,addingthenewtrait.
Notes
[1]genesegment[5segm[nt]n.基因节段
[2]sticky[5stiki]adj.黏的,黏性的
[3]beneficialtrait[beni5fiF[ltreit]n.有
益性状
[4]canola[kA5n[Ul[]n.双低(低芥酸、低硫甙)油菜
[5]geneticengineern.遗传工程师
[6]particlegunn.粒子枪
[7]monocot[5mRn[Uk[Ut]n.单 子 叶 植
物
[8]pellet[5pelit]n.小球
[9]tungsten[5tQNst[n]n.[化]钨
犈狊狊犪狔36 犌犲狀犲狊犪狀犱犕狅狀犲狔—犘犪狋犲狉狀犻狋狔犜犲狊狋[1]
1.ThegrowingsensitivityandfallingcostofDNAtechnologycreatesaboom[2]marketfor
paternitytests.Notlongafterher19yearoldsonwasmurderedtwoyearsago,JoyceMcFieldofBroadview,Ill.(Illinoise),wascontactedbyawomanwhosaidshewas
pregnantwithhischild.McFieldwasinclinedtobelieveher,andwhenthebabygirlwasborn,shebecameadottinggrandmother.Nowandthen,however,shewonderedifthegirlwasreallyhergranddaughter.Soonedayshetookasampleofhisdeadson’
sbloodthatthepolicehadkeptasevidenceandhiredaHoustoncompanycalledIdenti
genetoconductaDNApaternitytest.“Ijustwantedtheretobenoquestionmarks,”
saysMcField.Thetestsshowedthatthelittlegirlwasnotherson’s;McFieldhassinceseveredrelationswithboththewomanandthechild.McFieldisoneofarapidlygrowingnumberofpeoplewho,inthepostO.J.[3],postMonica[4]world,aretakingadvantageoftherapidlyfallingcostsofDNAtestingtechnologytosettlelingering[5]paternityquestions.Andwherethere’sanewscienceandagrowingneed,there’ssuretobeacompanythatcomesalongtofillit.IntheDNAtestingindustry,Identigeneisit.
2.Thoughanestimated200000DNAprofiles[6]areruneachyearbystatestryingtodocument[7]childsupportorwelfarepayments,folks[8]withpaternityissuesrarelyhavethewherewithal[9]toorderupatestontheirown.Aboutfiveyearsago,however,thatstartedtochange.ItwasthenthatCarolineCaskey,32,aFrenchliteraturemajorturnedbusinessstudent,thoughttocombinecuttingedge[10]DNAanalysiswithold
fashioned,tohawk[11]theproductmarketing.Afewyearsearlier,alabheadedbyherfatherThomascaskeypatentedsomethingcalledthe“shorttandemrepeat”[12],ashortcutmethodofsamplingDNA.Caskeysawthenewtechniqueforthecashcow[13]itcouldbeandfoundedIdentigene,advertisingherfather’stechniqueasasimpleand—
at$475atestaffordablewaytoestablishpaternity,launchinganadblitz[14]thatin
101
cludeddirectmail,TVtalkshowsandbillboards[15]in30U.S.cities,Caskeymadesureshegothercompanyinfrontoftheconsumers.
3.Consumersresponded.Identigene’sbusinesshasdoubledineachofthepastfiveyears.Thisyearthecompanyexpectstofield[16]67000telephoneinquiriesandconduct10,
000DNAtests,comparedwith650testsin1995.ItnowhasofficesinJapan,Korea,
BrazilandtheCzechRepublic.4.Thebusinessisnotwithoutcontroversy,however,mostofitcenteredontrickyquestionsofprivacy.ShorttandemtechnologyissosensitivethatitcanidentifyDNAfromlittlemorethanthesalivaresidueonasodacan.“Amoralprincipleingenetictestingisthatitshouldalwaysbedonewiththeconsentoftheindividual,”saysArthorCaplan,
directoroftheCenterforBioethics[17]attheUniversityofPennsylvania.“noonewantsotherssnooping[18]intohisDNA.”
5.Butsuchniceties[19]carrylittleweight[20]forpeopledesperatetoestablishsomethingasconsequential[21]aspaternity;andCaskeyplanstokeepcashingin[22]onthatneed.Identigeneispreparingtoofferanevencheaper,$150testthatwillprofile[23]newborns’DNAtoreassureanxiousparentsthatthey’releavingthehospitalwiththeirownchild.“It’spotentiallyamuchbiggermarketthanpaternitytesting,”saysCaskey.Anditisabiggerpayoff[24]too.
Notes
[1]boom[bu:m]n.繁荣,隆隆声
[2]paternity[p[5t[:niti]testn.亲 子 鉴
定
[3]O.J.即OrenthalJamesSimpson美国
超级橄榄球星。1994年6月12日晚,
O.J.辛普森的前妻妮科尔和她的男朋
友罗 恩·戈 德 曼 被 杀,辛 普 森 成 为 唯
一的嫌疑犯被捕受 审。这 一 事 件 轰 动
了美国。1995年10月 美 国 洛 杉 矶 刑
事陪审 团 裁 定 辛 普 森 谋 杀 案 不 成 立,致使辛普森在长达1年多的 刑 事 官 司
中 胜 诉。这 一 事 件 再 一 次 轰 动 了 美
国。美 国 舆 论 将 此 称 为“世 纪 审 判”,当时使用了DNA检验。
[4]Monica即 MonicaSamilleLewinsky(莫妮卡·萨米勒·莱温斯 基)。由 于
20世纪90年 代 她 在 美 国 白 宫 实 习 时
和当时 美 国 总 统 比 尔·克 林 顿 发 生
性行为 造 成 绯 闻,从 而 引 起 公 众 的 注
意。起初克 林 顿 不 承 认,但 莫 妮 卡 衣
物上精子的DNA与克林顿的相同,克
林顿不得不承认。[5]lingering[5liNg[riN]adj.拖 延 的,
依依不舍的
[6]profile[5prEufail]n.剖面,侧面,外
形,轮廓
[7]document[5dCkjum[nt]vt.为……提
供证明,提供文件
[8]folks[f[uks]n.[口]父母
[9]wherewithal[5wZ[wi:5TR:l]n.(常
做thewherewithal)必要的资金
[10]cuttingedgeadj.有高度竞争力的
[11]hawk[hC:k]vt.捕 捉,咳 出,兜 售,(沿街)叫卖,散播
[12]shorttandem [5tAnd[m]repeatn.(生化)短的串联重复
UNIT10 犕犗犔犈犆犝犔犃犚犅犐犗犔犗犌犢犃犖犇犜犚犃犖犛犌犈犖犐犆犛
102
[13]cashcown.财源
[14]adblitz[blitz]n.广告闪电战
[15]billboard[5bilbC:d]n.广告牌
[16]field[fi:ld]vt.圆满答复
[17]bioethics[5bai[ueWiks]n.生 物 伦 理
学
[18]snoop[snu:p]vi.探 听,调 查,偷 窃
n.到 处 窥 视,爱 管 闲 事 的 人,私 家 侦
探
[19]nicety[5naisiti]n.准确,精密,细微
[20]carrylittleweight无足轻重
[21]consequential[7kRnsi5kwenF[l]adj.重大的
[22]cashinv.收到……货款,赚钱
[23]profile[5pr[Ufail]vt.给……画侧面
图
[24]payoff[5peiR:f]n.发工资,付清,盈
利,回报(=payback)
犈狊狊犪狔37 犌犲狀犲犌狌狀[1]犛狆犲犲犱狊犛犲犪狉犮犺犳狅狉犖犲狑犗狉犮犺犻犱[2]犆狅犾狅狉狊
1.AcorngeneisgivingUSDepartmentofAgriculture(USDA[3])researchersajumpstart[4]inverifyingwhatthecolorofanewflowerwillbe.
2.“Iforchidplantsarebredforanewcolor,it’sanyone’sguessabouttheoutcome.Usually,theplantindustrynowwaitsthreeyearsuntilabloomappears.”saidRobertJ.Griesbach,aplantgeneticistwithUSDA’sAgriculturalResearchService.
3.“Wefoundacorngenethatwillgiveusresultsonthecolorofnewhybridsinjustthreedays,”hesaid.Thatgeneregulatesthepigmentincornplants.
4.Griesbachsaidthegenetictechnique—coatingthecornDNAonmicroscopicgoldpelletsthatarepropelled,byaparticlegun,intoorchidflowerpetals—screenforgeneticflaws[5]intheparentplantscrossedtobreednewhybrids.
5.“Thatshouldgiveplantbreedersahigherdegreeofcertainty[6]incrossingvariousorchidcolorslikepurpleandyellowbycuttingdownonthenumberofunwantedcolormutations,”hesaid.Aboutoneinathousandorchidplantslacksadequatepigments,
causingwhiteornearwhiteflowers.Othermutationsresultinflowerswithvaryingde
greesofpurplepigment,rangingtoabout25percentoftruepurplecolor.6.“Wehavetestedthetechniquesuccessfullyonbulbplantslikegladiolas[7]andotherornamentals[8]likepetunias[9],aswellasonorchids,”saidGriesbach,anexpertonflowerpigmentation.“Geneticscreeningcouldresultinabroaderrangeofcolorsinorchidsandotherornamentalplants.”
7.Griesbachsaidthetechniquecouldbe“aboon[10]tobreedersoforchidsbecauseoftheflower’slonggenerationtime— uptosixyearsinsomecommercialtypes.”Orchidflowersarehighlyprized[11],headded,notingthatpottedphalaenopsisorchids[12]are“fastbecomingamajoreconomiccrop[13].”Griesbachtriedthefastergenetictechniqueafterremovingwhitepetalsfromorchidflowers.Hebombardedthepetalswithmicoscopic(1mmindiameter)goldpelletscoatedwithDNAtakenfromcornplants.
8.“ScreeningplantsforcolormutationsisanewusefortheparticlegunthatBobGries
103
bachdemonstratedforthefirsttime”saidRogerLawson,NationalArboretum[14],
Washington,DC.“Thegoldpelletsweremorethan10timessmallerthanthedotattheendofthissentence.”Hesaid.Overmorethantwoyearsoftests,Griesbachfoundthattheintroducedcorngenescausenearwhiteflowerstogainpigmentswithin48hours.Onfullycoloredwildtypeflowers,thepurplecontinuedtodevelopforthenext24hours.“Eventually,theorchidcellswithcorngeneslookedthesameasthepurplecellsfoundinwildplants,withoutlossofpigment,”Griesbachsaid.
Notes
[1]GeneGunn.基因枪
[2]orchid[5R:kid]n.[植]兰,兰花,淡
紫色
[3]USDAn.美 国 农 业 部(USDepartmentofAgriculture)
[4]jumpstartn.大起步
[5]geneticflaw[flR:]n.遗传瑕疵
[6]certainty[5s[:t[nti]n.确定,确实的
事情
[7]gladiola[glAdi5[ul[]n.剑 兰,唐 菖
蒲
[8]ornamental[7R:n[5mentl]n.装饰植
物
[9]petunia[pi5tju:nj[]n.牵牛
[10]boon[bu:n]n.恩惠,实惠,福利
[11]prized[praizd]adj.珍贵的,价高的
[12]phalaenopsisorchid[fAlA5n[upsisC:
kid]n.蝴蝶兰
[13]economiccropn.经济作物
[14]NationalArboretum[7B:b[:5ri:t[m]
n.国家植物园
犈狊狊犪狔38 犘犪狋犲狀狋犻狀犵犌犲狀犲犛犲狇狌犲狀犮犲狊:犖狅狋犻狀狋犺犲犅犲狊狋犐狀狋犲狉犲狊狋狊狅犳犛犮犻犲狀犮犲狅狉犛狅犮犻犲狋狔
1.TheAmericanbiotechnologyindustrywasshockedwhensocialactivist[1]JeremyRifkin
organisedapetitiondrive[2]lastyeartostirreligiousoppositiontoanypatentson“therichgeneticresourcesoftheEarth’sbiologicalcommons[3],”includingmostespeciallyhumangenes.BySeptemberhehadsecured[4]thesignaturesof186RomanCatholic,
Protestant[5],Jewish,Buddhist,Hindu[6],andMuslimAmericanreligiousleadersona
petitioncallingforabanonbiologicalpatents.Theindustryrespondedwithastronglyworded[7]whitepaperontheimportanceofallowingpatentsforhumangenes,whichisnowbeingcirculatedwidelyamongAmericanreligiousscholars.
2.Butdespitethereligiousbattleground,America’sdiscussionofpatents,outsidetheo
logical[8]circles,isnotablysecular[9].Itisconductedprimarilyintermsofpriorlegal
precedents[10]andtheimportanceofpatentprotectiontofurtherprivatesectorfundingandresearch.Thisisreflectedinthefightthathaseruptedbetweentwobehemoths[11]
inthepharmaceutical[12]community.
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104
3.SmithKlineBeechamhasformedaconsortium[13]withanAmericancompany,Human
GenomeSciences,tomap,sequence,andpatentasmuchofthehumangenomeaspossible.Theconsortiumhassequencedabout850000fragmentsofDNAdrawnfromalmost85%ofthehumangenome.Roughly200ofthe450applicationsforhumangene
patentsfiled[14]intheUnitedStatescomefromtheconsortium.
4.ButofficialsatthepharmaceuticalgiantMerckdonotbelievethatthebasicsequencein
formationofthehumangenomeoughttobepatentable[15].Somesuggestthatthecom
pany’soppositionisinspiredbythefactthat,unlikeSmithKline,ithasnotformedanalliancewithanotherfirmthatheldpatentspendingonalargenumberofgenese
quences.Whateverthecompany’smotives[16]theyhavearguedpersuasivelythatloc
kingupthebasicstructuralanddescriptiveelements[17]ofthegenomebynarrowlyheld
patentprotectionswillnotensurethatthehumangenomeismaximallyexploitedforthe
publicgood[18].
5.MerckisnowsponsoringagroupatWashingtonUniversityinStLouistosequencethehumangenomeandmaketheinformationfreelyavailable.Currently4000newse
quencesarebeingidentifiedeachweek.Asof[19]lastmonth,355000sequenceshad
beenidentifiedandplacedinadatabaseinthepublicdomain.Thishascreatedaremarkablesituationinwhichtwocorporategiantsareengagedinacompetitioninwhichoneseekstogiveawaywhattheotherwishestosell.
6.EventheUnitedStatesgovernmentcannotquitemakeupitsmindaboutpatentinghu
mangenes.In1991theNationalInstitutesofHealth(NIH)[20]filedapplicationsfor
2375partialDNAsequences.Uproarensued[21],includingunfavourablereactionsfrom
othergovernments,andinFebruary1994theinstitutes’director,HaroldVarmus,announcedthewithdrawalofapplicationsfortheseandothersequencepatents.
7.Meanwhilethegovernmentfiledandreceivedapatentonthegenesofamemberofthe
Hagahaitribe[22]inPapuaNewGuinea[23],someofwhomhaveanunusualresistanceto
leukaemia[24].Thissetoffaninternationalcontretemps[25],withThirdWorldnations
protestingagainstexploitationoftheirnationalgenomicresourcesbyavaricious[26]sci
entistsfromeconomicallyprivilegednations.8.Theargumentthatitisimmoraltopatenthumangeneticsequencesseemsunlikelyto
prevailfortworeasons.Firstly,whilestrongtheologicalreservationsexist,itishardtoequateassigningapatenttoaDNAstripwithownershipofahumanbody.Sellingbodiesintoslaveryisexploitative,becauseourpersonalidentityissointimatelytiedtoourbodies.Itisnotsoobviouslyaviolationofthehumanspirittoassignrightstoexclusiveuseanddevelopmentoverasegmentofchromosome13toagovernmentagencyorabiotechnologyconcern.Secondly,thegeneticspatenttrainhaslongsinceleftthestation.ItisalreadywidelyacceptedinAmericaandinmanyEuropeancountriesthat
genesofknownfunction,betheyhumanorotherwise,arepatentable.Sequencingofindividualgenesisseenasbeingakintodiscovering“nonnaturallyoccurringcomposi
105
tionsofmatter,”andthereforemeetsthecriteriaforissuance[27]ofapatent— beingnew,useful,andnotobvious.
9.Ifthereisnopersuasivereasontoforbidthepatentingofhumangenes,theargumentmustturntoconsequences.Theissueisnolongerwhethergenescanbepatentedon
principle,butwhatsortofpatentsonwhatsortofgeneticinformationwillmostencouragethedevelopmentofusefulinventionsandproductsforpromotinghumanhealthandwellbeing.Whileaconvincingcasecanbemadeforthevalueofpatentsinsecuringinvestmentandattentionfromthosewhoholdthem,limitingaccesstoportionsofthehumangenometoasmallsetofscientistssimplybecausetheyidentifiedthesequencesfirstisunlikelytoleadtothemaximalintellectualexploitationofthisresource.Nordoesitmakemoralsense.Ifgovernmentfundshavebeenusedtomapandsequencethehumangenome,whyshouldthefruitsofthateffortbeturnedovertoasingleowner?
Permittingpatentsofsimplesegmentsofthegenome,ratherthanforproductsandinventions,wouldseemtobecontrarytothepublicinterest[28].
Notes
[1]activist[5Aktivist]n.活动家
[2]petitiondrive[pi5tiF[ndraiv]n.请愿
运动
[3]biologicalcommonsn.生 物 学 共 有 资
源
[4]secure[si5kju[]vt.获得
[5]Protestant[5prRtist[nt]n.新教徒
[6]Hindu[5hindu:]n.印度教教徒
[7]stronglywordedadj.措辞强硬的
[8]theological[Wi[5lCddVik[l]adj.神
学的,神学上的
[9]secular[5sekjUl[]adj.世 俗 的,平 凡
的
[10]priorlegalprecedent优先的法律先例
[11]behemoth[bi5hi:mCW]n.(圣经)河
马,巨兽,庞然大物
[12]pharmaceutical[7fB:m[5sju:tik[l]n.药物adj.制药(学)上的
[13]consortiumn.社团,协会,联盟,(国
际)财团,[律]配偶的权利,(美)大学
联盟协定
[14]file[fail]vt.把……归档,提 出(申 请
等)[15]patentable[5peit[nteibl]adj.可 专 利
化的,可取得专利的
[16]motive[5m[utiv]n.动机,目的
[17]descriptive[dis5kriptiv]elementsn.描述性成分
[18]publicgoodn.公众利益
[19]asof:在……时,到……时为止从……
时起
[20]NIHn.(美国)国家卫生研究所(NationalInstituteofHealth)
[21]ensue[in5sju:]vi.跟着发生,继起
[22]Hagahaitribe:巴 布 亚 新 几 内 亚 的 一
个微小部族,该 部 族 最 早 于1983年 才
与外界有所接触。不久,美国的科学家
发现,他们的血液含有一种毒素。这些
科学家认为,此毒素可用来发展治疗白
血病的新方法。[23]PapuaNewGuinea:巴布亚新几内亚独
立国(TheIndependentStateofPapua
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106
NewGuinea)为 英 联 邦 国 家。位 于 太
平洋西南 部。西 与 印 度 尼 西 亚 的 伊 里
安查亚省接壤,南隔托雷斯海峡与澳大
利亚相 望。属 美 拉 尼 西 亚 群 岛。是 印
度洋和太 平 洋 上 最 后 一 片 未 被 污 染 的
净土。[24]leukaemia[ljU:5ki:mi[]n.白血病
[25]contretemps[5kC:ntr[t[:N]n.意外
事故,不合时宜,令人尴尬的事,不幸的
[26]avaricious[7Av[5riF[s]adj.贪财的,
贪婪的
[27]issuance[5iFu:[ns]n.发行,发布
[28]publicinterest公共利益
107
犝犖犐犜11 犅犐犗犜犈犆犎犖犗犔犗犌犢
犈狊狊犪狔39 犘犾犪狀狋犜犻狊狊狌犲犆狌犾狋狌狉犲[1]
Introduction1.Planttissuecultureinvolvesthegrowingofplanttissuefromplantmaterialtakenfromasourceplant.Ithasbeenfoundthatplantscanreproducewholeplantsfromfragmentsofplantmaterialwhengivenanutrientmedia[2]capableofsupportinggrowthandappropriatehormonecontrol.
2.Thenutrientmediausedinplanttissuecultureisanagar[3]mediawithmacroandmicronutrients[4]dissolvedinit.Unlikeplantsgrowingfromaseed,tissueculturesrequireasupplyofcarboninanorganicformsuchassugars.Theyalsorequireaminoacids,Bvitaminsandgrowthhormones.Theconstituentsofthemediawillvarywiththeplantmaterialbeingcultured.
3.Planttissueculturecanbeusedtocloneplantsandproducemanyidenticalplantsforaparticularmarket.Thiscanbeusedwhenanewvarietyisgrownandothermethodsofcultivationaretooslowforthedesiredmarket.Itcanalsobeusedifastockplant[5]hasbeeninfectedandmaterialtakenfromtheplantthatisnotinfected.Theexcisedplantmaterialcanbegrownonandanydiseasefreeplantsgrownonforpropagation[6].Planttissuecultureisalsoofuseinresearchforbiochemists,geniticists,plantbreedersandplantpathologists[7].Planttissueculturehasalsoprovedmoreefficientintheproductionofsecondarymetabolites[8]thantheuseoftheparentplantsinvariousinstancesandhasbeenusedinthecommercialproductionofthenapthoquinonepigmentShikonin[9].Planttissueculturehasalsobeenusedintheproductionofflavours,sweeteners,naturalcolourantsandpharmaceuticals.Withtheadvent[10]ofgeneinsertion,plantcellswithgenematerialinsertedcanberegeneratedusingtissueculturetoproduceawholenewplant.Forexample,sugarbeetexplants[11]canbemicropropagated[12]toproducewholeplants.
4.Someplantsarebettersuitedtoplanttissueculturethanothersbutmostplantscanbecultivatedwithtimeandpractise.
MaterialsandMethods5.Whentakingplantmaterialtogrowonusingplanttissuecultureitisimportanttoget
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108
themostappropriatematerialfortheendproductyouareaimingfor.Planttissuehasbeenshowntobetotipotent[13],butdifferenttissueswillrequiredifferenttreatmentto
producewholeplantsifthatistheaim.Tissuethatisdividingsuchasatthenodesandleafaxils[14],leafpetiole[15]materialareoftenused.
6.Sharpcutswilldecreasetheamountofdecayingmaterialpresent,anddecreasethepossibilityofinfection.Theuseofasharpscalpel[16]isadvised.Forceps[17]arenecessarytomovetheplantmaterialtothegrowingmedia.Thecuttingshouldtakeplaceinasterileenvironmentandthegrowingmediaonlyexposedwhentheplantmaterialisplacedinit,afterwhichitshouldbesealed.
ForcepsScalpelDisinfectants[18]—forsurfaces,implementsandplantmaterial.LaminarFlowCabinet[19]
Bunsenburner[20]
Containerspetridishes,smallclearplasticcontainers,glassjars[21].GrowthmediaappropriatetoplantmaterialbeingculturedMurashigeSkoog[22]
Constituents Mediamg/LitreInorganicAmmoniumNitrate(NH4NO3) 1650PotassiumNitrate(KNO3) 1900CalciumChloride(CaCl2·2H2O) 440MagnesiumSulphate(MgSO4·7H2O) 370KH2PO4 170PotassiumIodide 0.83H3BO3 6.2ManganeseSulphate(MnSO4·4H2O) 22.3ZincSulphate(ZnSO4·7H2O) 8.6Na2MO4·H2O 0.25CopperSulphate(CuSO4·5H2O) 0.025IronSulphate(FeSO4·7H2O) 27.8Na2EDTA·2H2O 37.3Organic Inositol[23] 100
NicotinicAcid[24] 0.5 Pyridoxine[25]HCl 0.5 ThiamineHCl 0.1 Glycine 2 Sucrose 3%BVitamins
109
Nicotinicacid ThiamineHCl PyridoxineHClGrowthHormones Auxins[26]
BenzylAminoPurine[27]
Indoleaceticacid[28]
InositolCytokinins[29]
Kinetin[30]
Forgrowing,planttissueculturesonasuitablesiteisrequiredwhichisclean,warm(20℃)andthereisadequatelight.
7.Thesourceoftheplantmaterialisimportantassomeplanttissueisbettersuitedtotissueculturethanothers,theabilityofplantmaterialtogrowanddivideinvitroisknownastotipotency[31],butdifferentplantmaterialwillneeddifferentcontroltoformnewplantmaterial.Theplantmaterialmayformanewembryo,callus[32]tissueorawholeplantdependingonhowitislookedafter.
HistoryofPlantTissueCulture8.Thisabilityhasbeenknownformanyyearsandmuchinformationhasbeengatheredonthebestwaystolookafterplantmaterialofdifferentspeciesandsourcesfordifferentusesusingplanttissueculture.Vochtungin1878observedthatcellsalongastemslengthwerecapableofgeneratingrootsorshoots.GottliebHaberlandt,aGermanbotanist,wasthefirsttogeneratenewtissuefromfullydifferentiatedtissue.
9.Hanniggrewnearlymatureembryosofcrucifersandgrewthemtomaturityonmineralsaltsandsugarsolution.Theembryoswouldnotgrowtoformplantshoweverwithouttheadditionofgrowthcompounds.Laterworkwassuccessfulingrowingonembryoswiththeadditionofcoconutmilk[33].Nutrientmediathenincludedmineralsalts,vitamins,aminoacids,andsugar.Laibachsuccessfullyrearedembryosthatwereotherwiseunviable[34]usingtissueculture.Severalnewhybridshavesince‘evolved’usingtissueculturethatwouldotherwisehavebeenunviableattheembryostage.
10.WhitesuccesfullyrearedtomatorootculturesusingamediumcontainingthreeBvitamins,pyrodoxine,thiamineandnicotinicacid,alsoinorganicsaltsandsucrose.Inthe1030’sidentificationofauxinasanaturalgrowthregulatorandtherecognitionoftheimportanceoftheBvitaminsledtoimprovementsintissueculturepractices.Proliferationofcellswasachievedusingasolutioncontainingglucoseandcysteinehydrochloride[35].Thefirstcontinuallygrowingcultureswereachievedusingcarrotrootcambium[36].
11.Celldivisionintissuehadtoawaitthediscoveryofkinetin.Thiswasfirstdiscoveredbyautoclaving[37]freshlyisolatedslurriesofDNAfromHerring[38]sperm.Thediscoveryof
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110
cytokininsgavemuchimpetus[39]totissueculture.12.Techniquesdevelopedtostimulatecelldivisioninliquidculture.In1965wholeplants
wereraisedfromisolatedsinglecellsbyfilteringsuspensionculturesandgrowingontheisolatedcellsonsolidmediacontaining0.6%agar.Thesetechniquesarenowwidelyusedforcloningtissues.
13.Hormonalcontroloftissueculturewasachievedusingtheregulationofcytokinin:auxinratio,thuscontrollingrootandshootdevelopmentintobacco.Itthenbecamepossibletomanipulatetissuesandtodevelopwholeplantlets[40]viashootandrootdevelopment.Cellscouldalsobecontrolledtoproducesomaticembryos[41]whichcanthenbeusedtoproducewholeplants.Rapidpropagation[42]oftissuesfromcalluswasusedthoughgeneticvariationintissueculturetendedtooccur.Productionfromshoottip[43]andleafprimordia[44]provedamoresuccessfultechnique.Thetechniquewasusedtoproducevirusfreeplants[45]frominfectedDahlias[46].Orchidswerealsoclonedonawidescaleandthetechniquewasadaptedforferns,foliageplants[47]andfruitplants.
14.Growingoncytokininrichmediacanreduceapicaldominance[48]leadingtomoreshootsandtoquickerregenerationofnumbers.Invitrofertilization[49]madeitpossibletocrossvarietiesunabletocrossinnature.Haploidplantsoftobaccowereraisedfrompollengrains.Amorerecentdevelopmentintissuecultureisprotoplast[50]culture.Thistechniquehasallowedthecrossingofplantsbyprotoplastfusion[51],somatichybrids[52]
havethusbeenproducedofNicotianaglauca× Nicotianalangsdorfii.15.Tissuecultureisthusprovingtobeusefulinavarietyofwaysincludingplantpropagation,raisingandmaintenaceofhighhealthstatusplants,germplasm[53]storage,andavaluabletechniqueinplantimprovement.Inplantimprovementtissueculturemaybeusedinthetechniqueofgeneinsertiontoimproveplantstocks.
16.Planttissueculturehasalsobeenusedintheproductionofsecondarymetabolitesinplants.Theproductionofflavours,sweeteners,naturalcolourants,aswellaspharmaceuticalshasallachievedusingtissueculture.
Notes
[1]planttissueculturen.植物组织培养
[2]nutrientmedia[5nju:tri[nt5mi:dj[]
n.营养基
[3]agar[5eigB:]n.琼脂
[4]macroandmicronutrients大量和微量
营养
[5]stockplantn.母株
[6]propagation[7prRp[5geiF[n]n.(动
植物)繁殖,(声波,电磁辐射等)传播
[7]pathologist[p[5WRl[dVist]n.病理
学家
[8]secondarymetabolite[mi5tAb[lait]
n.次生代谢物
[9]napthoquinone[nApW[kwi5n[un]n.萘醌(即Shikonin:紫草素)
[10]advent[5Adv[nt]n.到来
[11]explant[eks5plAnt]n.外植体
[12] micropropagate [maikr[u 5prRp
111
[5geit]v.微繁殖
[13]totipotent[t[u5tip[t[nt]adj.(细胞)全能的
[14]axil[5Aksil]n.叶腋
[15]petiole[5peti[ul]n.叶柄,柄部
[16]scalpel[5skAlp[l]n.解剖刀
[17]forceps[5fR:seps]n.镊子,钳子
[18]disinfectant[disin5fekt[nt]n.消毒剂
[19]LaminarFlowCabinet[5lAmin[fl[U5kAbinit]n.层流橱柜
[20]Bunsenburner[5bQnsn5b[:n[]n.本生灯(即煤气灯)
[21]glassjar(实验室用)玻璃缸,玻璃瓶
[22]MurashigeSkoogn.MS培养基
[23]inositol[i5n[Usit[Ul]n.肌醇
[24]nicotinicacid[7nik[5tinik5Asid]n.烟酸,尼克酸
[25]pyridoxine[7pi[ri5dRksin]n.吡哆醇
(维生素B6)[26]auxin[5C:ksin]n.生长素类
[27]6benzyl[5benzil]aminopurine6苄
氨基嘌呤
[28]indoleacetic[5ind[ul[5si:tik]acid吲
哚乙酸
[29]cytokinin[5sait[u5kinin]n.细胞分裂素
[30]kinetin[5kain[tin]n.激动素
[31]totipotency[t[J5tip[t[nsi]n.全能性
[32]callus[5kAl[s]n.愈伤组织,皮肤的
硬结组织,胼胝,老茧
[33]coconut[5k[Uk[nQt]milkn.椰奶
[34]unviable[Qn5vai[bl]adj.不能独立生
存的
[35]cysteinehydrochloride[5sistin7haidr[u5klR:raid]n.盐酸半胱氨酸
[36]cambium[5kAmbi[m]n.[植]形成层
[37]autoclave[5R:t[ukleiv]n.(烹 调 用)高压锅,高压灭菌器
[38]herring[5heriN]n.青鱼,鲱
[39]impetus[5impit[s]n.推动力,促进
[40]plantlet[5plB:ntlit]n.小植物,苗
[41]somaticembryo[s[U5mAtik5embri[u]n.体细胞胚胎
[42]rapidpropagation快繁
[43]shoottip茎尖
[44]leafprimordia[prai5mC:dj[]n.叶原
基
[45]virusfreeplant无病毒植株
[46]dahlia[5deilj[]n.[植]大丽花
[47]foliage[5f[uliidV]plantn.观叶植物
[48]apical[5Apik[l]dominancen.顶端优
势
[49]invitro [in5vi:tr[u]fertilizationn.体外受精
[50]protoplastn.原生质体
[51]protoplastfusion原生质体融合
[52]somatichybrid体细胞杂种
[53]germplasm [plAzm]n.[生]种 质,生
殖细胞的细胞质
犈狊狊犪狔40 犆犾狅狀犻狀犵犜犲犮犺狀犻狇狌犲狊
1.Whatiscloning?Whatarecloningtechniques?Cloningreferstothedevelopmentofoff
springthataregeneticallyidenticaltotheirparent.Animalswhichreproduceasexual
ly[1]areexamplesofclonesthatareproducednaturally.
2.Thankstoadvancesingenetics[2]however,cloningcanalsooccurartificiallybyusingcertaincloningtechniques.Cloningtechniquesarelaboratoryprocessesusedtoproduceoffspringthataregeneticallyidenticaltothedonorparent.
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112
3.Clonesofadultanimalsarecreatedbyaprocesscalledsomaticcellnucleartransfer[3].Therearetwovariationsofthismethod.TheyaretheRoslinTechniqueandtheHonoluluTechnique.Itisimportanttonotethatinallofthesetechniquestheresultingoffspringwillbegeneticallyidenticaltothedonorandnotthesurrogate[4],unlessthedonatednucleusistakenfromasomaticcellofthesurrogate.
CloningTechniquesSomaticCellNuclearTransfer4.Thetermsomaticcellnucleartransferreferstothetransferofthenucleusfromasomaticcelltoaneggcell.Asomaticcellisanycellofthebodyotherthanagermcell[5].Anexampleofasomaticcellwouldbeabloodcell,heartcell,skincell,etc.
5.Inthisprocess,thenucleusofasomaticcellisremovedandinsertedintoanunfertilizedeggthathashaditsnucleusremoved.Theeggwithitsdonatednucleusisthennurtured[6]anddividesuntilitbecomesanembryo.Theembryoisthenplacedinsideasurrogatemotheranddevelopsinsidethesurrogate.
TheRoslinTechnique6.TheRoslinTechniqueisavariationofsomaticcellnucleartransferthatwasdevelopedbyresearchersattheRoslinInstitute.TheresearchersusedthismethodtocreateDolly[7].
7.Inthisprocess,somaticcells(withnucleiintact)areallowedtogrowanddivideandarethendeprivedofnutrientstoinducethecellsintoasuspendedordormantstage.Aneggcellthathashaditsnucleusremovedisthenplacedincloseproximity[8]toasomaticcellandbothcellsareshockedwithanelectricalpulse.Thecellsfuseandtheeggisallowedtodevelopintoanembryo.Theembryoisthenimplanted[9]intoasurrogate.
TheHonoluluTechnique8.TheHonoluluTechniquewasdevelopedbyDr.TeruhikoWakayamaattheUniversityofHawaii.Inthismethod,thenucleusfromasomaticcellisremovedandinjectedintoaneggthathashaditsnucleusremoved.Theeggisbathedinachemicalsolutionandcultured.Thedevelopingembryoisthenimplantedintoasurrogateandallowedtodevelop.
WhyUseTheseTechniques?
9.Researchershopethatthesetechniquescanbeusedinresearchingandtreatinghumandiseasesandgeneticallyalteringanimalsfortheproductionofhumantransplantorgans.
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Notes
[1]asexually[A5seksju[li]adv.无 性 地,无性生殖地
[2]geneticsn.遗传学
[3]somaticcellnucleartransfer体 细 胞 核
转移
[4]surrogate[5sQr[git]n.代理,代用品,代理人vt.使代理,使代替
[5]germcell生殖细胞
[6]nurture[5n[:tF[]n.养 育,教 育,教
养,营养品vt.养育,给予营养物,教养
[7]Dolly[5dCli]n.多莉(克隆羊)[8]proximity[prRk5simiti]n.接近,亲近
[9]implant[im5plB:nt]v.移植,植入
犈狊狊犪狔41 犎狅狑狋狅犆犾狅狀犲犪犎犲狉犱?
1.FirsttherewasDollytheScottishsheep.ThenlastJuly,cameseverallittersofclonedmice[1].NowscientistsatJapan’sKinkiUniversityhaveproducedsomethingevenbiggerandagooddealtastier:eightidenticalcalvesclonedfromasinglecow.
2.Writinginlastweek’sissueofScience,TheJapaneseresearchersreportthattheyachievedthisfeatofbovinephotocopyingusingtwodifferenttypesofcells,takenfromasinglecow’sovariesandfallopiantubes[2].Thosecells—allcarryingthesamegeneticpayload— wereintroducedintocowova[3]whosegeneshadbeenscoopedaway.Tensuchidenticalembryoswerethenimplantedinthewombsofsurrogatecowmothers,
andallbuttwocametoterm.3.NooneknowswhytheKinkiteammanagedtobat[4]8outoften(whileDolly’screatorsneeded29embryostogetonehit).Japanesescientistshopetolearnmorewhenothercalves—clonedfromliver,kidney,andheartcells—arebornnextspring.Thebeefindustryisanxiouslyawaitingtheanswer:theclonescomefromalineofprize[5]cowswhosemeatsellsfor$100apound.
Notes
[1]mice[mais]n.小鼠(pl)[2]fallopian[fR:5l[UpjB:n]tuben.输卵
管
[3]ova[5[Uv[]n.卵(ovum的复数)[4]batvt.命中
[5]prizeadj.第一流的
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犈狊狊犪狔42 犆犾狅狀犲狊:犃狊犕犪狀狔犜狑犻狀狊犪狊犢狅狌犔犻犽犲
1.Whenagardener[1]wantstogrowanewplant,hecanoftentakeacutting[2]fromasingleparentplant.Fromonestemorleafhecangrowanentireplant.Intheanimalkingdom[3],ofcourse,weneedtwoparentsfortheproductionofaneworganism:wecannotcutoffatoe[4]andgrowababyfromit.ButinJune1966ateamofOxfordbiologistsannouncedinthemagazineNaturethattheyhadgrownsevenfrogsfromtheintestinalcellsofotherfrogs.Inotherwords,theyhadmanagedtousethegardener’stechniquewithananimal.
2.Basically,whattheydidwastoexchangethegenesinthefrog’scells.Theystartedoffwithafrog’segg.Theyremovedthenucleus,whichcontainsallthegenes,andreplaceditwiththenucleusfromabodycellofanotherfrog.Theythenimplantedtheeggwithitsnewnucleusinafemalefrogandcausedittostartdeveloping.Theeventualresultwasanormalfrog.Butbecausetheneweggnucleuscamefromanotherfrog’sbodycell,whichcontainsthecompletedoublesetofgeneticinstructionsofitsowner,thenewfrogwasgeneticallyidenticaltothatoriginalfrog.Itcontainednoneofitsmothers’genesatall,andnoneofthegenesfromtheoriginalegg.Ifonedoesthisseveraltimesusingthesamedonor,takingthenucleusfromthesame‘parent’,theresultisawholesetor‘clone’ofidenticaltwins.Theyarenotonlyidenticaltoeachother.Theyarealsoidenticaltotheirparent.
3.Thenextstepwastoclonelandanimalssuchassheepandcows.Thesurgeryinvolvedwasmoredelicate[5],fortheseanimalshavesmallereggswithtougherouterskins,butthetechniqueistechnicallyfeasible[6]inhumans.Sointheory,itispossibleforustoreproduceexactcopiesofourselves.Possible,perhaps,butisitlikely?
4.Agreatdealofnonsensehasbeenwrittenaboutthedangersofcloning.Wickedrulerscouldturnoutunlimitednumbersofidenticalpeopleandcreatearmiesofsoldiersorslaves.Butforfivethousandyearsithasbeenperfectlypossibleforpowermadrulerstopickoutcertainhumanbeingsandbreedthemselectively,creatingspecializedtypes,
justashumanshavebredcowsanddogs.Norulerhaseversucceededindoingso,becausenoneoftheirsubjects[7]wouldstandfor[8]it.Besides,ifonewantsaspecializedarmyofmen,itisfareasierandquickertotrainthem.Whatruler,howevermad,
wouldbewillingtowaittwentyyearsforhisarmytogrowup?
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Notes
[1]gardenern.园丁
[2]cuttingn.切段
[3]animalkingdom 动物界
[4]toen.趾,脚趾,足尖
[5]delicateadj.脆弱的,微妙的,棘手的
[6]feasibleadj.可行的,切实可行的
[7]subject[5sQbdVikt]n.国民
[8]standfor忍 受;代 表;象 征,倡 导 或 者
支持
犈狊狊犪狔43 犛狋犲犿犆犲犾犾狊犪狀犱犜犺犲犻狉犝狊犲狊
Whatarestemcells?
1.Stemcells[1]areunspecialized[2]cellsthathavetwoimportantcharacteristicsthatdistin
guishthemfromothercellsinthebody.First,theycanreplenish[3]theirnumbersforlongperiodsthroughcelldivision.Second,afterreceivingcertainchemicalsignals,theycandifferentiate[4],ortransformintospecializedcellswithspecificfunctions,suchasaheartcellornervecell.
2.Stemcellscanbeclassifiedbytheextenttowhichtheycandifferentiateintodifferentcelltypes:Totipotentstemcells[5]candifferentiateintoanycelltypeinthebodyplustheplacenta[6],whichnourishestheembryo.Afertilizedeggisatypeoftotipotentstemcell.Cellsproducedinthefirstfewdivisionsofthefertilizedeggarealsototipotent.Pluripotentstemcells[7]aredescendantsofthetotipotentstemcellsoftheembryo.Thesecells,whichdevelopaboutfourdaysafterfertilization,candifferentiateintoanycelltype,exceptfortotipotentstemcellsandthecellsoftheplacenta.Multipotentstemcells[8]aredescendentsofpluripotentstemcellsandantecedentsofspecializedcellsinparticulartissues.Forexample,hematopoieticstemcells[9],whicharefoundprimarilyinthebonemarrow[10],giverisetoallofthecellsfoundintheblood,includingredbloodcells,whitebloodcells,andplatelets.Anotherexampleisneuralstemcells[11],
whichcandifferentiateintonervecellsandneuralsupportcellscalledglia[12].3.Progenitorcells[13](orunipotentstemcells[14])canproduceonlyonecelltype.Forexample,erythroidprogenitorcells[15]differentiateintoonlyredbloodcells.
4.Attheendofthelongchainofcelldivisionsare“terminallydifferentiated”[16]cells,
suchasalivercellorlungcell,whicharepermanentlycommittedtospecificfunctions.Thesecellsstaycommittedtotheirfunctionsforthelifeoftheorganismoruntilatumordevelops.Inthecaseofatumor,thecellsdedifferentiate[17],orreturntoalessmaturestate.
5.Researchisnowbeingconductedonbothadultandembryonicstemcellstodetermine
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thecharacteristicsandpotentialofbothtocuredisease.
Whatarethesourcesofstemcells?
6.Therearethreesourcesofstemcells:
Embryonicstemcells(ESCs)[18]arederivedfrom4to5dayoldembryos.Atthisstage,theembryosaresphericalandareknownasblastocysts[19].Eachblastocystconsistsof50to150cellsandincludesthreestructures:anouterlayerofcells,afluidfilledcavity,andagroupofabout30pluripotentcellsatoneendofthecavity.Thislattergroupofcells,calledtheinnercellmass[20],formallthecellsofthebody.
7.ESCculturesarecreatedinthelaboratorybytransferringtheinnercellmassfromablastocystintoaspeciallytreatedplasticculturedish.Thecellsdivideand,afterseveraldays,begintocrowdtheculturedish.Whenthishappens,thecellsareremovedand
plated[21]intoseveralfreshculturedishes.Thisprocessisrepeatedmanytimes,eventuallyyieldingmillionsofESCs.If,aftersixmonths,thecellskeepdividingwithoutdifferentiating,arestillpluripotent,andaregeneticallynormal,theyarereferredtoasanESCline[22].
8.TheblastocystsusedforcreatingESClinesarederivedfromeggsthatwerefertilizedininvitrofertilizationclinicsbutneverimplantedinawoman’suterus.Theresultingembryoswerefrozenandlaterdonatedforresearchpurposeswiththeinformedconsentofthedonors.Currently,thereareover400000unusedfrozenembryosinU.S.fertilityclinics.
9.BecauseESCsarepluripotentandrelativelyeasytogrowincellculture,theyareattractivecandidatesforuseinstemcelltherapies[23].However,justinjectingESCsintoasiteofinjurywouldprobablyresultinatumorgrowinginthatspot.ESCsmustfirstbedirectedtodifferentiateintothedesiredcells,suchasheartmusclecells,bloodcells,ornervecells.TocontrolESCdifferentiationincellcultures,scientiststrydifferenttechniques,suchaschangingthechemicalcompositionoftheculturemedium,alteringthesurfaceoftheculturedish,orinsertingspecificgenesintothecells.
10.OnepossibledrawbacktousingdifferentiatedESClinesinstemcelltherapiesisthatESCsfromonepersonmightillicitanimmuneresponsewhenplacedintoanotherperson,becausetheproteinsontheESCsurfacesmightbeviewedasforeignbytherecipient’simmunesystem.However,thisisfarfromcertain.ESCderivativeshavebeentransplantedbetweenspecies(forexample,pigstorats)withoutbeingrejected,sothepossibilityexiststhatESCderivativesfromonepersonmightbesafelytransplantedintoanotherperson.Studiesinvestigatingthishaveyettobedone.
11.Adultstemcellsareundifferentiatedcellsthatarefoundinsmallnumbersinmostadulttissues.However,theyarealsofoundinchildrenandcanbeextractedfromumbilicalcord[24]blood.Amoreaccuratephraseis“somaticstemcells[25],”althoughthisphrasehasyettobegenerallyadopted.
12.Theprimaryrolesofadultstemcellsinthebodyaretomaintainandrepairthetissuesin
117
whichtheyarefound.Theyareusuallythoughtofasmultipotentcells,givingrisetoacloselyrelatedfamilyofcellswithinthetissue.Anexampleishematopoieticstemcells,
whichformallthevariouscellsintheblood.13.Recentevidence,however,indicatesthatsomeadultstemcelltypesmaybepluripotent,
oratleastabletodifferentiateintomultiplecelltypes.Forexample,hematopoieticstemcellscandifferentiateintoneurons,glia,skeletalmusclecells,heartmusclecells,
andlivercells.Whethertheyactuallydothisordinarilywithinthebodyisunknown.14.Bloodfromtheplacentaandumbilicalcordthatareleftoverafterbirthisarichsource
ofhematopoieticstemcells.Thesesocalledumbilicalcordstemcellshavebeenshowntobeabletodifferentiateintobonecellsandneurons,aswellasthecellsliningtheinsideofbloodvessels.
15.Apotentialadvantageofusingadultstemcellsfromapatientisthatthepatient’sowncellscouldbeexpandedinculture,treatedtodifferentiateintothedesiredcells,andthenreintroduced[26]intothepatient.Theuseofthepatient’sowncellswouldeliminateanypossibilitythattheymightberejectedbytheimmunesystem.Disadvantagesofusingadultstemcellsarethattheyarerareinmaturetissuesanditismoredifficulttoexpandtheirnumbersincellculture,comparedwithESCs.Embryonic(orfetal)germcellsarepluripotentstemcellsderivedfromsocalledprimordialgermcells[27],whicharethecellsthatgiverisetothegametes(spermandeggs)inadults.Scientistsobtain
primordialgermcellsfromtheareaina5to9weekoldembryo/fetusdestinedtobecomeeitherthetesticles[28]ortheovaries(thedividinglinebetweenembryoandfetusistheendofthe8thweek).LikeESCs,theprimordialgermcellsaretransferredintoaspeciallytreatedplasticculturedish,wheretheyformgermcellcolonies[29].
16.Lessresearchhasbeenperformedusingembryonicgerm(EG)cellsthanESCs,mostlybecausetheembryosusedforderivingEGcellsaredeliberatelyaborted[30],whiletheblastocystsusedforderivingESCsareproducedthroughinvitrofertilizationinafertilityclinic.EGcellsarealsodifficulttomaintainincellculturebecausetheyhaveatendencytodifferentiatespontaneously.
UsesofStemcells17.Upto128millionAmericansareaffectedbydiseasesforwhichresearcherslooktostemcelltechnologyforpromiseoftreatment.Whattheycurrentlyknowindicatesthatadultstemcellshavealimitedabilitytodifferentiateintousefultissues,fetalstemcellshaveagreatercapacitytodoso,andEScellsarethoughttobeabletodifferentiateintoanyotherkindofcell.Thedifferenttypesofcellsallhavepromisingapplications;hereisanoverview:
ChildhoodOnsetDiabetes[31]
18.InType1Diabetes,thecellsinthepancreasthatproduceinsulinareattackedbytheimmunesystem.Therehavebeenattemptstotreatitbytransplantingpancreaticcells,
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buttheimmunosuppressivedrugs[32]requiredtoperformthetransplantarehardforthebodytohandle,andthenumberoftransplantsavailableisverysmall.Stemcellscouldbeengineeredtodifferentiateintothebetacellsresponsibleforinsulinproduction,andtheycouldbemanipulatedtominimizethepossibilityofanimmuneresponsethatusuallyimpairs[33]transplants.
NervousSystemDiseases19.Therearecertaincellsinthebodythatreachmaturationandnolongeractivelydivide.
Nervecellsareanexampleofsuchcells.Therefore,ifthesecellsaredamagedordestroyed,thereisnorepairorreplenishmentoccurring.Thisisonedeterrentfromusingdrugs;theyareknowntodamageandkillcellsofthenervoussystem.Unfortunately,
peopleafflicted[34]withcertaintraumas[35]ordiseasestoofthenervoussystemsuchasmultiplesclerosis,Alzheimer’sdisease[36],Parkinson’sdisease[37],donothaveachoice.
20.Researchersseestemcellsasapotentialtreatmenttosuchdiseases.Forexample,participantsinParkinson’sstudieshaveshownsomeprogressafterfetalcellimplantationinpreliminarytrials.Studiesonrodents[38]havealsoproduceddesirableresultswhensubjectedtosimilarconditions.Perhapsatreatmentforsuchdebilitating[39]diseasesandinjuriesisinourfuture.
21.Evenincaseswhereactivelydividingcellsaredamaged,stemcelltreatmentisdesired.Indiseasesandinjuriesofthebonesandcartilage[40],ifdifferentiatedstemcellscouldbetransplantedintopatients,perhapslongtermdamagecouldbealleviated[41].Examplesarearthritis,bonefractures[42],andchondrodysplasia[43].
ImmunodeficiencyDiseases22.Notonlyhavestemcellsshownpromiseinnervoussystemtraumasanddiseases,buttheycouldpotentiallybeusedintreatmentofprimary(congenital)andsecondary(acquired)immunodeficiencydiseases[44].Thesediseasesarisewhenanimmunefunctionisunderdeveloped,suppressed,orabsent.ExamplesofsuchdiseasesareThymicaplasia(DiGeorgesyndrome)[45],WiskottAldrichsyndrome[46],andAIDS.Ifpluripotentstemcellscouldbetransplantedtopatientswithautoimmunediseases[47],theymaybeabletodirecttheimmunesystemtofunctionnormally.
Cancer23.Finally,stemcellscanbemanipulatedintobecomingbonemarrowstemcells.Suchcellsarecurrentlyusedintreatingpatientswithdeficiencies,suchaspostchemotherapy[48]
cancerpatientswithsomeeffectiveness.Futurestudiesareaimedatdevelopingtreatments,whicharemoresuccessfulinhopesofloweringsideaffectsfromchemotherapy.
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Notes
[1]stemcell干细胞
[2]unspecialized[5Qn5speF[laizd]adj.未特化的
[3]replenish[ri5pleniF]v.补充
[4]differentiate[7dif[5renFieit]v.分化
[5]totipotentstemcelln.全能干细胞
[6]placenta[pl[5sent[]n.胎盘,胎座
[7]pluripotent[plJ[5rip[t[nt]stemcelln.多能(性)的干细胞
[8]multipotentstemcelln.多 效(性)的
干细胞
[9]hematopoietic [7hem[toU5pRitik]
stemcelln.造血的干细胞
[10]bonemarrow[5mAr[u]n.骨髓
[11]neuralstemcelln.神经干细胞
[12]glia[5gli:[]n.神经胶质
[13]progenitorcelln.起源细胞
[14]unipotent[ju5nip[t[nt]stemn.单能
性干细胞
[15]erythroid[5eriWrCid]progenitorcelln.红系造血祖细胞
[16]terminallydifferentiated终 极 分 化 了
的
[17]dedifferentiatevi.去分化
[18]embryonicstemcell(ESC)n.胚 胎 干
细胞
[19]blastocyst[5blAst[usist]n.胚泡
[20]innercellmassn.内细胞群
[21]platev.铺板
[22]ESClinen.胚胎干细胞系
[23]stemcelltherapy[5Wer[pi]n.干 细
胞治疗
[24]umbilical[7Qmbi5laik[l]cordn.脐带
[25]somaticstemcell体细胞干细胞
[26]reintroduce[5ri:7intr[5dju:s]vt.再
导入
[27]primordialgermcell原始生殖细胞
[28]testicle[5tesikl]n.睾丸
[29]colony[5kCl[ni]n.[生]群体
[30]deliberatelyaborted故意流产的
[31]ChildhoodOnsetDiabetesn.儿童期发
作糖尿病
[32]immunosuppressive[7imjun[us[5presiv]
drugn.免疫抑制药物
[33]impair[im5pZ[]v.削弱
[34]afflict[[5flikt]vt.使痛苦,折磨
[35]trauma[5trR:mE]n.外伤,损伤
[36]Alzheimer’sdiseasen.阿 尔 茨 海 默 病
(即老年痴呆)[37]Parkinson’sdiseasen.帕 金 森 氏 症,
震颤性麻痹
[38]rodent[5r[ud[nt]n.啮齿动物
[39]debilitate[di5biliteit]vt.使 衰 弱,使
虚弱
[40]cartilage[5kB:tilidV]n.软骨
[41]alleviate[[5li:vieit]vt.使(痛苦等)易于忍受,减轻
[42]bonefracture骨折
[43]chondrodysplasia[7kCndr[udis5pleizi[]n.软骨发育异常,软骨发育不良
[44]immunodeficiencydisease免疫缺陷病
[45]thymicaplasia[5Waimik [5pleizi[](DiGeorgesyndrome)胸腺发育不全,胸腺成形 不 完 全,胸 腺 先 天 萎 缩;DiGeorge综合症
[46]WiskottAldrichsyndrome WiskottAldrich综合症
[47]autoimmune[C:t[ui5mju:n]disease自体免疫疾病
[48]postchemotherapy [p[Jst 7kem[U5Wer[pi]adj.化疗后的
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犈狊狊犪狔44 犠犺犪狋犐犳犕狔犜犲狊狋犜狌犫犲犅犪犫犻犲狊犠犲狉犲犛狑犪狆狆犲犱[1]
犻狀狋犺犲犔犪犫?
1.MyheartgoesouttoDonnaFasano.She’stheNewYorkCitywomanwhowasreluctantlythrustintotheheadlines[2]lastweekbecauseofaninfertilitytreatment[3]mixedupthatimpregnated[4]herwithtwoembryos:onecreatedbyhereggandherhusband’
ssperm,theotherbyanAfricanAmericancouplewhohadbeenseeingthesamespecialistatthesametime.Shecarriedbothembryostoterm[5],givingbirthtotwobeautifulbutnoticeablydifferentboysandraisingthemforthreemonths,duringwhichtimetheysharedthesamecrib[6],thesameswing[7]andthesameparents.Thenwhenablackcouplecameforthclaimingtobethebiologicalparents[8]ofoneoftheirtwins,shefacedatrulySolomonic[9]testoflove.
2.Themindreels.Likethousandsofwomenmyage,I’mintimatelyfamiliarwiththeemotionalrollercoaster[10]ridethatisinvitrofertilization.Fouryearsago,myhusbandandIwereblessedwithourowntesttubebabies[11]beautifulgirltwinswhoareequallydelightfulbuttotallydifferent.Onelooksjustlikeme;theotherbearslittleresemblance.Aretheybothmine?Weremyeggsplacedintherightdrawer?IntherightPetridish?Fertilizedbytherightsperm?Issomeoneelseraisingoneofmychildren?Isignorancebliss?
3.Reproductivemedicinehascomealongwayinaveryshorttime.Itisnowa$1billionayearindustrythataccountsforsome23000livebirthsayearintheU.S.Butitswellpublicizedmishapshavemoralovertones[12].Areweinterferingwiththenaturalorderofthings,allowingdoctorstoplayGod?
4.Forthosewhochoosetoplayitsroulettewheel[13],babymakingtechnologyisbothheartwrenching[14]andexpensive(asmuchas$18000foraprocedure[15]).Itinvolvessophisticateddrugsthatyoumustinjectintoyourselfdailyandwhoselongtermtoll(cost)maybeyetunknown.Butthepossiblereturn?Amiracle!
5.LastweekFasanoannouncedshehadagreedtosurrender[16]custody[17]ofherblacksontotheblackcouple,pendingthefinalresultsofaDNAtest.Amotherwasgivingupasonwhomshehadborneandwhomsheloves;anotherwomanwasreceivingthegiftoflife.Twocoupleswhohadseparatelymadethedecisiontoundergotheinvasive[18]proceduresofmodernreproductivemedicineandplacetheirfaithinthehandsofalltoofallible[19]infertilityexpertsarenowpermanentlyjointogether,theirprivatelivespublic,
theirsonsforeverbrothers.
Notes
[1]swap[swCp]n.v.交换 [2]headline[5hedlain]n.大字标题
121
[3]infertilitytreatment[inf[5tiliti5tri:
tm[nt]n.不育治疗
[4]impregnate[5impregneit]vt.使怀孕,使受精,使充满,注入,灌输
[5]carry……toterm足月分娩
[6]crib[krib]n.婴儿床
[7]swing[swiN]n.秋千
[8]biologicalparents生物学父母
[9]Solomonic[5sCl[m[nik]adj.像Solomon那 样 需 要 智 慧 的。Solomon(?
~932BC)所 罗 门,以 色 列 国 王,在 位
期间,发 展 贸 易,以 武 力 维 持 其 统 治,使犹太达到鼎盛,以智慧著称。
[10]rollercoaster[5r[ul[5k[ust[]n.旋
转木马车;翻滚过山车,云霄飞车(一
种上有敞篷 的 小 型 车 厢 且 快 速 行 驶 的
有急转弯的大坡度高架轨道,尤指游乐
园中的乘坐装置)[11]testtubebabyn.试管婴儿
[12]overtone[5[uv[t[un]n.[音]泛 音,暗示,折光的色彩
[13]roulettewheel[ru:letwi:l]n.轮盘赌
[14]heartwrenching[5rentFiN]adj.绞
心般的
[15]procedure[pr[5si:dV[]n.疗 程,程
序,手续
[16]surrender[s[5rend[]vt.交出,放弃,使投降,听任
[17]custody[5kQst[di]n.保管,监护权
[18]invasive[in5veisiv]adj.入侵性的
[19]alltoofallible[5fAl[bl]adj.太 易 出
错的
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犝犖犐犜12 犌犈犖犗犕犐犆犛犃犖犇犘犚犗犜犈犗犕犐犆犛
犈狊狊犪狔45 犌犲狀狅犿犻犮狊
1.Genomicsisthestudyofanorganism’sgenomeandtheuseofthegenes.Itdealswiththesystematicuseofgenomeinformation,associatedwithotherdata,toprovideanswersinbiology,medicine,andindustry.
2.Genomicshasthepotentialofofferingnewtherapeutic[1]methodsforthetreatmentofsomediseases,aswellasnewdiagnosticmethods.Otherapplicationsareinthefoodandagriculturesectors.Themajortoolsandmethodsrelatedtogenomicsarebioinformatics[2],geneticanalysis,measurementofgeneexpression,anddeterminationofgenefunction.
History3.Genomicsappearedinthe1980sandtookoff[3]inthe1990swiththeinitiation[4]ofgenomeprojectsforseveralspecies.Therelatedfieldofgeneticsisthestudyofgenesandtheirroleininheritance.
4.Thefirstgenometobesequencedinitsentirety[5]wasthatofbacteriophageFX174(5,
368kb)in1980.ThefirstfreelivingorganismtobesequencedwasthatofHaemophilusinfluenzae[6](1.8Mb)in1995;andsincethengenomesarebeingsequencedatarapidpace.Aroughdraft[7]ofthehumangenomewascompletedbytheHumanGenomeProject[8]inearly2001amidmuchfanfare[9].
Thegrowthofthe“omics”
5.Theoriginaluseofthesuffix“ome”(fromtheGreekfor‘all’,‘every’or‘complete’)
was“genome”,whichreferstothecompletegeneticmakeupofanorganism.Becauseofthesuccessoflargescalequantitativebiologyprojectssuchasgenomesequencing,thesuffix“ome”hasbeenextendedtoahostofothercontexts.Theonlyother“ome”toshakeitsoriginasabuzzword[10]isproteome[11],thetotality[12]ofproteins(expressedgenesthataretranslated)inanorganism,tissuetypeorcell,andproteomics[13]isnowwellestablished.
Comparativegenomics[14]
6.Comparisonofgenomeshasresultedinsomesurprisingbiologicaldiscoveries.Ifaparti
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cularDNAsequenceorpatternispresentamongmanymembersofaclade[15],thatsequenceissaidtohavebeenconservedamongthespecies.EvolutionaryconservationofaDNAsequencemayimplythatitconfers[16]arelativeselectiveadvantagetotheorganismsthatpossessit.Conservationalsosuggeststhatsequencehasfunctionalsignificance[17].Itmaybeaproteincodingsequenceorregulatoryregion.ExperimentalinvestigationofsomeofthesesequenceshasshownthatsomearetranscribedintosmallRNAmolecules,althoughthefunctionsoftheseRNAswerenotimmediatelyapparent.
7.Theidentificationofsimilarsequences(includingmanygenes)intwodistantlyrelatedorganisms,butnotinothermembersofoneoftheclades,hasledtothetheorythatthesesequenceswereacquiredbyhorizontalgenetransfer[18].Thisphenomenonismostprominentinthermophilicbacteria[19],whereitseemsthatgenesweretransferredfromArchaea[20]toEubacteria[21].Ithasalsobeennoticedthatbacterialgenesexistineukaryoticnucleargenomesandthatthesegenesgenerallyencodemitochondrialandplastidproteins,givingsupporttotheendosymbiotictheoryoftheoriginoftheseorganelles.
Geneticsimilarity[22]
8.ItisoftenstatedthataparticularorganismsharesXpercentofitsDNAwithhumans.Thisnumberindicatesthepercentageofbasepairsthatareidenticalbetweenthetwospecies.Hereisalistofgeneticsimilaritytohumans,withsources,whereknown.Whilethesenumberscomefromvarioussecondarysources,thedatamayhaveoriginatedfrommeasuresofDNADNAhybridizationorfromdirectsequencecomparisons.
Species Similarity Source
Human
Chimpanzee[23]
Bonobo[25]
Gorilla
Mouse
Dog
C.elegans
Banana
Daffodil
99.9%quotedbyPresidentClinton,Jan2000,StateoftheUnionaddress;
alsoHumanGenomeProject
100% identicaltwins
98.4%sources:AmericansforMedicalProgress;JonEntineintheSan
FranciscoExaminer
98.7% RichardMuralofCeleraGenomics,quotedonMSNBC[24]
equaltochimpanzee
98.38%basedonstudyofintergenicnonrepetitiveDNAinAmJHumGen
et.(2001)Feb;682:444~456
98% source:AmericansforMedicalProgress
85% comparingallproteincodingsequences,NHGRI[26]
95% JonEntineintheSanFranciscoExaminer
74% JonEntineintheSanFranciscoExaminer
50% source:AmericansforMedicalProgress
35% StevenRoseinTheGuardian22Jan2004
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Notes
[1]therapeutic[Wer[5pju:tik]adj.治疗
的,治疗学的
[2]bioinformatics[bai[u5infR:5mAtiks]
n.生物信息学
[3]takeoffv.起飞
[4]initiation[i7niFi5eiF[n]n.开始
[5]entirety[in5tai[ti]n.全部,完全
[6]Haemophilusinfluenzae[hem[5filEsinfljU:enzB:]流感嗜血杆菌
[7]roughdraftn.框架图
[8]HumanGenomeProject人类基因组计
划 (HGP)[9]fanfaren.喇 叭 或 号 角 嘹 亮 的 吹 奏 声,
吹牛
[10]buzzword[bQzw[:d]n.时髦词汇
[11]proteome[5pr[uti[um]n.蛋白组
[12]totality[t[u5tAliti]n.全体,总数
[13]proteomics[5pr[uti5[umiks]n.蛋 白
组学
[14]comparative[k[m5pAr[tiv]genomicsn.比较基因组学
[15]clade[kleid]n.[生]进化支,分化支
[16]confer[k[n5f[:]vt.授予(称号、学 位
等),赠与,把……赠与,协议
[17]functionalsignificance功能意义
[18]horizontalgenetransfer水平基因转移
[19]thermophilic[7W[m[5filik]adj.嗜
热的
[20]archaea[B:5ki:[]n.古细菌
[21]eubacteria[5jU:bAk5ti[ri[]n.真 细
菌(即bacteria细菌)[22]geneticsimilarity遗传相似性
[23]chimpanzee[5tFimp[n5zi:]n.黑猩猩
[24]MSNBC:是 一 个 综 合 性 的24小 时 新
闻频道以及在线新闻服务供应商,创立
于1996年7月15日,是 由 微 软(MS)与NBC(国家广播公司)联合创立的。
[25]bonobo[5b[un[7b[u]n.(产于非洲刚
果河以南的)倭 黑 猩 猩[源 自 非 洲 当 地
语][26]NHGRI:美 国 人 类 基 因 组 计 划 研 究 所
(The NationalHuman GenomeResearchInstitute,NHGRI)
犈狊狊犪狔46 犚犻犮犲犌犲狀狅犿犲犠狅狉犽犆狉犲犪狋犲狊犎狅狆犲
1.Accordingtocolumnist[1]SmithfromCNNEWS[2]Science,thesequencingoftherice
genomewhichmayturnouttobeevenmoreimportantthanthesequencingofthehumangenomeinsomewaysaspassedalmostunnoticedSmithsaysthatbecauseofgeneticsimilarities,discoveriesmadeusingthericegenomewilltranslatewitheasetowheat,
barley,sorghum[3],millet[4]andahostofothers.Wemight,infact,begintospeakof
acerealgraingenome.Intheshortterm,though,itisricethatwillbeimportant,be
causericefeedsaninordinate[5]numberofus.Since1965,infact,theworld’sricepro
ductionhasbeengrowingat2.5percentayearenoughtokeeppacewithhumanity’s
hungrybellies[6].
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2.Thatmiracle,saysSmith,hasbeenwrought[7]usingstandardbreedingtechniquestoproducehighyieldvarieties.(Betterirrigationandincreasedaccesstocreditalsoplayedarole,accordingtotheInternationalRiceResearchInstitute,IRRI[8]).
3.Butstandardbreedingisyourclassicalblackbox.Youcrosssomeplants,observetheircharacteristicsandthencrosssomemore,hopingtocomeupwithanimprovement.Youdon’tknowwhat’sgoingoninsidetheplant.
4.Intheshortterm,saysSteveBriggs,knowingthericegenomewillletstandardbreederspeepinsidetheblackbox[9]andguidetheireffortsmoreefficiently.
5.BriggsisheadoftheTorreyMesaResearchInstitute[10]inLaJolla,Calif.,which,fortherecord,sequencedthericegenome.Alsofortherecord,theTorreyMesaResearchInstituteisthegenomicsresearchcenterforacompanycalledSyngenta,whichwasformedlastNovemberwhenNovartisAgribusinessandZenecaAgrochemicalsmerged.
6.SoSmithsayshecanhearthisnow.Onemorebiginternationalbiotechcompanyhasaproprietorial[11]interestinsomethingofvitalinteresttosmallfarmersinAsia.Timetobreakouttheplacards[12]andthetomatofish[13]suit.ButSyngentahaslearnedalessonortwofromthepastfewyears.Thericegenomewillbeavailablewithoutfeesorroyalty[14]paymentstoresearchcentersintheThirdWorld.Itwillalsobeavailablefreetoacademicscientists.
7.Now,ricebreedersintheThirdWorldwillhaveapowerfulnewtoolattheirdisposal.Forthefirsttime,Briggssaid,theywillknowatthelevelandwhat’sgoingonwhentheymakeacross.And,withanyluck,theymaybeabletocomeupwithvarietiesthatwillcontinuetofillthebillionsofstomachs.
8.BriggsaddsthatSyngentaalsohopesthatthenewknowledgewillallowitsownplantbreederstoimprovecerealcropseithernutritionallyorintermsofyieldandthoseimprovementswouldbeforsale.Inthelongrun,Briggswascitedassaying,Syngentahopestomatchgenetotraitsinaprocesscalledgenomicswithsufficientaccuracythatbiotechtoolscantakeoverfromtraditionalplantbreeding.Soinsteadofcrossingplantsandintheprocessmixingupthegenes,thebiotechnicians[15]wouldmanipulatethegenesdirectly.
Notes
[1]columnist[5kRl[mnist]n.专栏作家
[2]CNNEWSn.美国有线电视新闻
[3]sorghum[5sR:g[m]n.高粱
[4]millet[5milit]n.小米
[5]inordinate[in5R:dinit]adj.过 多 紊
乱的
[6]humanity’shungrybelly人 类 饥 饿 的
肚皮
[7]wrought[rR:t]adj.work的 过 去 式
和过 去 分 词;做 成 的,形 成 的,精 炼
的,[冶](金属)锻造的
[8]InternationalRiceResearchInstitute.IRRI国际水稻研究所
[9]blackboxn.黑箱
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[10]TorreyMesaResearchInstituten.美
国托雷梅萨研究院
[11]proprietorial[prRprai[5tR:ri[l]adj.所有权的
[12]placard[5plAkB:d]n.布告,张贴
[13]tomatofishn.番茄鱼
[14]biotechnician[bai[5tekniF[n]n.生物
工程学家
犈狊狊犪狔47 犛犮犻犲狀狋犻狊狋狊犆狉犪犮犽犌犲狀犲犆狅犱犲狅犳犚犻犮犲
1.Scientistshavedecodedthegeneticblueprintofrice,astaple[1]forhalftheworld’spop
ulation,inabreakthroughthatcouldleadtohardiervarietiesandeasemalnutrition[2],
researcherssaidFriday.Italsocouldspeedresearchonmorecomplexgrainssuchascornandwheat.Riceisthefirstplantimportanttoagriculturetohaveitsgenomemapped.Itsmodelissimple,butitalsoissosimilartoothergrainsthatscientistscanusethericemaptolocategenesinthosecrops.Thatwouldmakeiteasiertoaddnutrientstocropsormakethemmoreresistanttodroughtandpeststhroughconventionalbreedingorgeneticengineering.“Identifyingnotonlythegenes,butalsotheirfunctionsandhowtheywork,willprovideresearcherswithcrucialnewknowledgetoim
provefoodcrops”,saidSteveBriggs,presidentoftheTorreyMesaResearchInstitute,
asubsidiary[3]ofSwitzerlandbasedSyngenta.2.TheprojectwasajointeffortofSyngentaandMyriadGeneticsInc.ofSaltLakeCity.ThebiotechcompaniesarefinishingaheadofaninternationalricegenomeprojectbasedinJapanthatisusingdifferentmappingtechniquesandresearchfunddonatedbySyn
gentarivalMonsantoCo.Thetwoprojectshavefollowedsimilartrackstorivalpublicandprivateeffortstodecodethehumangenome.Theinternationalriceproject,tobefinishedin2003,issupposedtobemoreaccurateandcomplete.Syngenta’sprojectmayraisequestionsaboutcorporatecontrolofgeneticmaterial,particularlybecauseitinvolvesacropthatisvitaltomanypoornations.
3.Thetwocompaniessaidtheywouldmakethericedataavailabletootherresearchersthroughresearchcontracts.Syngentasaiditalsowouldworkwithresearchinstitutesin
poorcountriestohelpfarmers.Thecompany’spolicyistoprovidedata,suchasthe
geneticcodeforrice,withoutroyalties[4]orfeeswhenitisusedforresearchbenefitingpoorfarmers.“IfSyngentafulfillsthatpolicy,poorfarmersmayreapsubstantialbenefits,”saidPerterPinstrupAndersen,directoroftheInternationalFoodPolicyResearchInstitute.Hecautioned[5],however,that“itwilltakemanyyearsofscientificstudybeforetheseadvancesreachthefieldsofsmallscalefarmers.Thesoonertheseeffortsareunderway,thebetter”.
4.Datafromtheinternationalprojectwillbefreelyavailabletoscientistsworldwide.Riceisarelativelypoorsourceofmanyessentialnutrients,butscientistsaredevelopingvarietiesenhancedwithvitaminAtopreventblindnessinAsianchildren.Hardiervarieties
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alsoareneeded.Riceproductionhasdoubledinthepast30yearsbutisnotexpandingenoughtokeeppacewithmanycountries’populationgrowth.
5.Lastyear,scientistscompletedthemappingofanotherplant,arabidopsis[6],butthericegenomeismoresimilartoothergrasses,includingwheat,cornandbarley,thattogetherwithricearetheworld’smainsourcesoffoodandanimalfeed.Riceplantshave12chromosomescontainingabout50,000differentgenes,whichinturnmakeupabout430millionbasepairsofDNA.Thewheatgenomeis37timeslarger,butrecentresearchhasfoundthatgrassgenomeshavesimilargeneticmapsoverlargeblocksofthechromosomes.Awheatbreedercouldusethericemaptofindasimilargeneinwhichtomakethatcropresistanttofungus,amajorpesttofarmers,saidBenjaminBurr,aplantgeneticistattheBrookhavenNationalLaboratoryinNewYork.
Notes
[1]staple[5steipl]n.主粮作物
[2]malnutrition[5mAlnju:5triF[n]n.营
养不良
[3]subsidiary[s[b5sidj[ri]adj.辅 助 的,补充的n.分支机构
[4]royalty[5rRi[lti]n.使用费,版税 ,专利权税
[5]caution[5kR:F[n]n.小心,谨慎,警
告vt.警告
[6]arabidopsis[[5rAbi5d[Upsis]n.拟南芥
犈狊狊犪狔48 犌狉犪犻狀狊狅犳犎狅狆犲
1.Atfirst,thegrainsofricethatIngoPotrykussiftedthroughhisfingersdidnotseemat
allspecial.Butoncetheirdark,crinklyhusks[1]werestrippedawayandtheinteriors
polishedtoaglossysheen,Potrykuscouldbehold[2]theseeds’goldensecret.Attheir
core,thesegrainswerenotthepearlywhiteofordinaryricebutaverypaleyellowcour
tesy[3]ofbetacarotene[4],thenutrientthatserves,asabuildingblockforvitaminA.
Potrykuswaselated.Formorethanadecadehehaddreamedofcreatinggoldenrice[5]
thatwouldimprovethelivesofmillionsoftheworld’spoorestpeople.Atleast1millionchildren,weakenedbyvitaminA deficiency,dieeveryyearandanadditional350,000goblind.Potrykussawhisriceasthemodeststartofanewgreenrevolution:
bananasthatwouldn’trotonthewaytomarket,cornthatcouldsupplyitsownfertilizer,wheatthatcouldthriveindroughtriddensoil.Butimaginingagoldenricewasonething,Potrykusfound,andbringingoneintoexistencequiteanother.Yearafteryear,
heandhiscolleaguesranintounexpectedobstacles,beginningwiththefinicky[6]grow
inghabitsofthericetheyhadtransplantedtoagreenhouse[7]nearthefoothillsoftheSwissAlps.Andwhensuccessfinallycameinearly1999,Potrykus,65andaboutto
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retireasaprofessorattheSwissFederalInstituteofTechnologyinZurich,facedevenmoreformidablechallenges.Thegoldenricethatheandhiscolleaguesdevelopedisa
productofgeneticengineering,whatopponents[8]callFrankenfood[9].Assuch,itwasentangled[10]inawebofhopesandfearsandpoliticalbaggage[11],nottomentionafistfulofironclad[12]patents.
2.ForaboutayearnoweversincePotrykusandhischiefcollaborator,PeterBeyeroftheUniversityofFreiburginGermany,announcedtheirachievement,theirgoldengrainhasilluminatedanincreasinglypolarized[13]publicdebateovergeneticallyengineeredcrops.LastmonthPotrykusandBeyerarrivedinthePhilippinescarryinggoldenriceseedsandgeneticmaterialboundforIRRI.ThegoalofIRRIscientistswillbetodevelopgoldentropicalrice,basedonthetechniquesPotrykushasusedforhistemperatericevariety.Andthisisonlythefirststep.Twoprivatecompanies,SwissbasedSyngentaandMyriadGeneticsofSaltLakeCityintheU.S.revealedlastweekthattheyhavemappedtheentirericegenome,pavingthewayforotherdramaticbreakthroughs.Yearsoflabworkonaviablegeneticallymodified(GM)ricevarietyarestillneeded,
butscientistsinAsiawillundoubtedlyfindtheirricesubjectedtothesamekindofhostilesuspicionandscrutiny[14]thathasalreadyledtocurbs[15]onthecommercializationofthesecropsinBritain,Germany,SwitzerlandandBrazil.
3.Theincreasinglyacrimonious[16]debateovergeneticallyengineeredcropseruptedthemomenttheymadetheircommercialdebut[17]inthemid1990s.Europeanenvironmentalists[18]andconsumeradvocacygroups[19]werethefirsttolaunchmajorproteststhathavesincespreadworldwide.EnvironmentalistsinIndiahavefiledsuitagainstMonsantotopreventitfromtestinggeneticallymodifiedcotton.InthePhilippines,farmershavedemonstratedagainstseedgiantsMonsantoandDupont’sfieldtestsofBtcorn.AndactiviststherepointtoMiracleRiceproductoftheGreenRevolutioninthe’60sisacautionarylesson.ItswholesaleadoptioninSoutheastAsialedtoaricemonoculture[20],makingcropsmorevulnerabletoinsectpestsanddisease,andmoredependentonpesticides.Publichostilityisunderstandable.Mostofthegeneticallyengineeredcropsintroducedsofarrepresentminorvariationsonthesametwothemes:resistancetoinsectpestsandtoherbicidesusedtocontrolthegrowthofweeds.Andtheyareoftenmarketedbylarge,multinationalcorporationsthatproduceandselltheveryagriculturalchemicalsfarmersaresprayingontheirfields.SowhilemanyfarmershaveembracedsuchcropsasMonsanto’sRoundupReadysoybeans,withtheirgeneticallyengineeredresistancetoMonsanto’sRoundupbrandherbicide,thatletthemsprayweedkillerwithoutharmingcrops,consumershavecometoregardsuchthingswithmountingsuspicion.Whyresorttoastrangenewtechnologythatmightharmthebiosphere,
theyask,whenthebenefitsofdoingsoseemsmall?Indeed,thebenefitshaveseemedsmalluntilgoldenricecamealong.Goldenriceisthefirstcompelling[21]exampleofa
geneticallyengineeredcropthatmaybenefitnotjustthefarmerswhogrowitbutalsotheconsumerswhoeatit.Nowondersomanyofthoseconcernedaboutpovertyand
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hungerareconvincedthatsuchcropshaveacriticalroletoplayinfeedingtheworld.China,oneofthefirstcountriestogrowgeneticallyengineeredtobaccoandcottoncommercially,isinvestingheavilyinthetechnologyasawaytocombatitschronicdomesticfoodproblems.C.S.Prakash,ascientistattheCenterforPlantBiotechnologyResearchatTuskegeeUniversityinAlabama,recentlyaccusedantiGMactivistsofbeing“wellfedfolk[22]”who“jet[23]aroundtheworld”todisrupttechnologythatwillbenefitthepoor.AccordingtoPrakash“Biotechnologyisoneofthebesthopesforsolvingfoodneedwhenwehave6billionpeopleandcertainlyinthenext30to50yearswhentherewillbe9billionontheglobe”.
4.Indeed,bytheyear2020,thedemandforgrain,bothforhumanconsumptionandforanimalfeed,isprojectedtogoupbynearlyhalf.Addtothattheneedtoconserveoverstressedwaterresourcesandreducetheuseofpollutingchemicals,andtheenormityofthechallengeisapparent.
GoingFortheGold5.Inthelate1980s,afterhebecameafullprofessor[24]ofplantscienceattheSwissFederalInstituteofTechnology,IngoPotrykusstartedtothinkaboutusinggeneticengineeringtoimprovethenutritionalqualitiesofrice.Ofsome3billionpeoplewhodependonriceastheirmajorstaple,around10%risksomedegreeofvitaminAdeficiencyandthehealthproblemsthatresult.TheprobleminterestedPotrykusforanumberofreasons.Forstarters,hewasattractedbythescientificchallengeoftransferringnotjustasingle
gene,asmanyhadalreadydone,butagroupofgenesthatrepresentedakeypartofabiochemicalpathway.Hewasalsomotivatedbyempathy[25].AsachildgrowingupinwarravagedGermany,Potrykusandhisbrotherswereoftensodesperatelyhungrythattheyatewhattheycouldsteal.
6.Around1990,PotrykushookedupwithGaryToenniessen,directoroffoodsecurityfortheRockefellerFoundation.ToenniessenhadidentifiedthelackofbetacaroteneinpolishedricegrainsasanappropriatetargetforgenescientistslikePotrykustotacklebecauseitlaybeyondtheabilityoftraditionalplantbreedingtoaddress.Forwhilerice,
likeothergreenplants,containslighttrappingbetacaroteneinexternaltissues,itdoesnotproducebetacaroteneinitsendosperm (thestarchyinteriorpartofthericegrainthatmostpeopleeat).
7.AtaRockefellersponsoredmeeting,PotrykusmettheUniversityofFreiburg’sPeterBeyer,anexpertonthebetacarotenepathwayindaffodils.Theydecidedtocombinetheirexpertise.In1993,withsome$100,000inseedmoneyfromtheRockefellerFoundation,PotrykusandBeyerlaunchedwhatturnedintoasevenyear,$2.6millionproject,backedbytheSwissgovernmentandtheEuropeanUnion.“Iwasinaprivilegedsituation,”reflectsPotrykus,“becauseIwasabletooperatewithoutindustrialsupport.Onlyinthatsituationcanyouthinkofgivingawayyourworkforfree.”Thetwoscientistssoondiscovered,however,thatgivingawaygoldenricewasnotgoingto
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beeasy.Thegenestheytransferredandthebacteriatheyusedtotransferthosegeneswereencumberedbypatentsandproprietaryrights.OnlyafterextensivenegotiationshavethetwoscientistsmanagedtostrikeadealwithSyngenta,MonsantoandthefourothercompaniesthatheldexclusivelicensestothetechnologiesusedbyPotrykusandBeyertocreategoldenrice.InexchangeforcommercialmarketingrightsintheU.S.andotheraffluentmarkets,thecompaniesrecentlyagreedtodonatethetechnologyfreetodevelopingcountries.
8.Still,criticsofagriculturalbiotechnologyerupted.“Aripoff[26]ofthepublictrust,”
grumbledtheRuralAdvancementFoundationInternational,anadvocacygroupbasedinWinnipeg,Canada.Potrykuswasdismayedbysuchnegativereaction.“Itwouldbeirresponsible,”heexclaimed,“nottosayimmoral,nottousebiotechnologytotrytosolvethisproblem!”
Weighing[27]thePerils9.Beneaththehyperbolic[28]talkofFrankenfoods,evenproponentsofagriculturalbiotechnologyagree,liesomerealconcerns.Tobeginwith,allfoods,includingthetrans
genicfoodscreatedthroughgeneticengineering,arepotentialsourcesofallergens.That’sbecausethetransferredgenescontaininstructionsformakingproteinsandsome
proteinsthoseinpeanuts,forexamplecauseallergicreactions.Thenthereistheproblemof“geneticpollution,”[29]asopponentsofbiotechnologytermit.Pollengrainsfromsuchwindpollinated[30]plantsascorn,forinstance,arecarriedfarandwide.Thecontinuingflapover[31]Btcornandcotton.Thegeneofacommonsoilbacteria(Bacillusthuringiensis),anaturalinsecticide,istransferredtotheplantsasprovidedmorefodder[32]forthedebate.Ecologistsareconcernedthatwidespreadplantingofthesecropswillspur[33]Btresistanceamongcroppests,andBtispopularwithorganicfarmers[34].Evenmoreworrisomeareecologicalconcerns.In1999CornellUniversityentomologistJohnLoseyperformedaprovocative,“seatofthepants”[35]laboratoryexperiment.HedustedBtcornpollenonplantspopulatedbymonarchbutterfly[36]caterpillars.Manyofthecaterpillarsdied.LoseyhimselfisnotyetconvincedthatBtcornposesagravedangertoNorthAmerica’smonarchbutterflypopulation,buthedoesthinktheissuedeservesattention.Othersagree.“Theproblemwithtransgenicsistherisksandhazardsinvolved,”saysAshishKothariofKalpavriskh,anIndianenvironmentalgroupworkingtopreservethecountry’sbiodiversity.“Westilldon’tknowwhatthiscandotootherplantsandorganisms.”
10.Therearemorepotentialpitfalls.Amongotherthings,thepossibilityexiststhatastransgenesinpollendrift[37],theywillfertilizewildplants,andweedswillemergethatarehardierandevenmoredifficulttocontrol.Nooneknowshowcommontheexchangeofgenesbetweendomesticplantsandtheirwildrelativesreallyis,butMargaretMellon,directoroftheUnionofConcernedScientists’agricultureandbiotechnologyprogram,isnotaloneinthinkingthatit’shightimewefindout.Saysshe:“Peopleshould
131
berespondingtotheseconcernswithexperiments,notassurances[38].”
11.Thatisbeginningtohappen,althoughcontrarytoexpectations.Thereportscominginarenotthatscary.Forthreeyearsnow,UniversityofArizonaentomologistBruceTabashnikhasbeenmonitoringfieldsofBtcottonthatfarmershaveplantedinhisstate.Andinthisinstanceatleast,hesays,“theenvironmentalrisksseemminimal,andthebenefitsseemgreat.”Firstofall,cottonisselfpollinated[39]ratherthanwindpollinated,sothatthespreadoftheBtgeneisoflessconcern.AndbecausetheBtgeneissoeffective,henotes,Arizonafarmersreducedtheiruseofchemicalinsecticides75%.Sofar,thepinkbollworm[40]populationhasnotrebounded[41],indicatingthatthefearedresistancetoBthasnotyetdeveloped.
AssessingthePromise12.Arethecriticsofagriculturalbiotechnologyright?Isbiotech’spromisenothingmorethanoverblown[42]corporatehype[43]?Thepapaya[44]growersinHawaii’sPunadistrictclamortodisagree.In1992anepidemic[45]ofpapayaringspotvirus[46]threatenedtodestroythestate’spapayaindustry;by1994,nearlyhalfthestate’spapayaacreagehadbeeninfected,theirownersforcedtoseekoutsideemployment.Butthenhelparrived,
intheformofavirusresistanttransgenicpapayadevelopedbyCornellUniversityplantpathologistDennisGonsalves.
13.In1995ateamofscientistssetupafieldtrialoftwotransgeniclinesUHSunUPandUHRainbow.Thenontransgenicplantsinthefieldtrialwereastunted[47]messandthetransgenicplantswerehealthy.In1998,afternegotiationswithfourpatentholders,
thepapayagrowersswitchedenmasse[48]tothetransgenicseedsandreclaimedtheirorchards.“Consumeracceptancehasbeengreat,”reportsRustyPerry,whorunsapapayafarmnearPuna.“We’vefoundthatcustomersaremoreconcernedwithhowthefruitslookandtastethanwithwhethertheyaretransgenicornot.”Thewidespreadperceptionthatagriculturalbiotechnologyisintrinsicallyinimical[49]totheenvironmentperplexesGordonConway,theagriculturalecologistwhoheadstheRockefellerFoundation.Heviewsgeneticengineeringasanimportanttoolforachievingwhathehastermeda“doublygreenrevolution.”[50]Ifthetechnologycanmarshal[51]aplant’snaturaldefensesagainstweedsandviruses,ifitcaninducecropstoflourishwithminimalapplicationofchemicalfertilizers,ifitcanmakedrylandagriculturemoreproductivewithoutstraininglocalwatersupplies,thenwhat’swrongwithit?Ofcourse,thesebreakthroughshavenothappenedyet.ButasPotrykusseesit,thereisnoquestionthatagriculturalbiotechnologycanbeharnessedforthegoodofhumankind.Theonlyquestioniswhetherthereisthecollectivework.
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Notes
[1]husk[hQsk]n.(果类或谷物的)外壳
(通常用复数),皮,无价值之物vt.剥
……的壳,削
[2]behold[bi5h[uld]vt.把……视为vi.看
[3]courtesy[5k[:tisi]n.谦恭,允许,礼
貌
[4]carotene[5kAr[ti:n]n.[生 化]胡 萝
卜素
[5]goldenricen.金稻米
[6]finicky[5finiki]adj.过分注意的,过
分讲究的,过分周到的
[7]greenhouse[5gri:nhaUs]n.温室
[8]opponent[[5p[un[nt]n.反对者
[9]Frankenfood[5frAnkenfu:d]n.基因
工程食品
[10]entangle[in5tANgl]vt.使 缠 上,纠
缠,卷入,连累,使混乱
[11]politicalbaggagen.政治包袱
[12]ironclad[ai[n5klAd]adj.装甲的,打
不破的
[13]polarize[5p[Jl[raiz]v.(使)偏 振,(使)极化,(使)两极分化
[14]scrutiny[5skru:tini]n.详细审查
[15]curb[k[:b]n.抑制
[16]acrimonious[7Akri5m[unj[s]adj.严
厉的,辛辣的
[17]debut[5debjU:]n.v.初 次 登 场,开
张
[18]environmentalist[in9vai[r[n5mentlist]
n.环保论者
[19]consumeradvocacygroup消费者觉悟
团体
[20]monoculture [5mRn[UkQltF[]n.[农]单一栽培,单作
[21]compelling [k[m5peliN]adj.强 制
的,强迫的,引人注目的
[22]wellfedfolk吃饱了的国民
[23]jetv.乘喷气机
[24]fullprofessorn.正教授
[25]empathy[5emp[Wi]n.移 情 作 用,[心]神入
[26]ripoffn.偷窃
[27]weighvt.称……重量,称,掂量vi.重
(若干)[28]hyperbolic[7haip[:5bClik]adj.双曲
线的,夸张的
[29]geneticpollutionn.遗传污染
[30]windpollinated[5pRlineit]adj.风媒
传粉的
[31]flapovern.争议不决
[32]foddern.饲料,草料,(创作的)素材,
弹药
[33]spur[sp[:]v.鞭策,刺激,疾驰,驱
策
[34]organicfarmer有机农民
[35]seatofthepantsadj.经验性的,基于
直觉和经验而不是推理的
[36]monarchbutterfly帝王蝶
[37]pollendrift花粉飘逸
[38]assurance[[5Fu[r[ns]n.断言
[39]selfpollinatedadj.自花授粉的
[40]bollworm[5b[Jlw…m]n.一 种 蛾 的
幼虫,螟蛉
[41]rebound[ri5baund]n.回弹v.回弹
[42]overblown[[uv[5bl[un]adj.停 息
的,盛开过的
[43]hype[haip]n.(美 俚)皮 下 注 射,骗
局,大肆宣传,大做广告,瘾君子
[44]papaya[p[5pai[]n.番 木 瓜 树,番 木
瓜果
[45]epidemic[7epi5demik]adj.流 行 的,
133
传染的,流 行 性n.时 疫,疫 疾 流 行,(风尚等的)流行,流行病
[46]ringspot[riNspRt]virusn.环斑病毒
[47]stunted[5sQntid]adj.成 长 受 妨 碍
的,矮小的
[48]enmasse [enmAs]adv.全 体 地,一
同地
[49]inimical[i5nimikl]adj.敌意的,有害
的
[50]doublygreenrevolutionn.双 重 绿 色
革命
[51]marshal[5mB:F[l]n.元帅,典礼官,执行官,司仪官vt.整顿,配置,汇集
vi.排列,集合
犈狊狊犪狔49 犘狉狅狋犲狅犿犻犮狊
1.Proteomics[1]isthelargescalestudyofproteins,particularlytheirstructuresandfunctions.Thistermwascoinedtomakeananalogy[2]withgenomics,andisoftenviewedasthe“nextstep”,butproteomicsismuchmorecomplicatedthangenomics.Mostim
portantly,whilethegenomeisaratherconstantentity[3],theproteomeisconstantlychangingthroughitsbiochemicalinteractionswiththegenomeandtheenvironment.Oneorganismwillhaveradically[4]differentproteinexpressionindifferentpartsofitsbody,indifferentstagesofitslifecycleandindifferentenvironmentalconditions.
2.Theentiretyofproteinsinexistenceinanorganismthroughoutitslifecycle,oronasmallerscaletheentiretyofproteinsfoundinaparticularcelltypeunderaparticulartypeofstimulation,arereferredtoastheproteomeoftheorganismorcelltyperespectively.
3.Withcompletionofaroughdraftofthehumangenome,manyresearchersarenowlookingathowgenesandproteinsinteracttoformotherproteins.AsurprisingfindingoftheHumanGenomeProjectisthattherearefarfewergenesthatcodeforproteinsinthehumangenomethanthereareproteinsinthehumanproteome(~22,000genesvs~200000proteins).Thelargeincreaseinproteindiversityisthoughttobeduetoalternativesplicing[5]andposttranslationalmodificationofproteins[6].
4.Tocatalogue[7]allhumanproteinsandascertain[8]theirfunctionsandinteractionspresentsadauntingchallengeforscientists.Aninternationalcollaborationtoachievethese
goalsisbeingcoordinatedbytheHumanProteomeOrganization.
Branchesofproteomics5.Proteinseparation.Basictoallproteomictechnologiesareproteinseparation,theseparationofacomplexmixturesothatindividualproteinsaremoreeasilyprocessedwithothertechniques.
6.Proteinidentification.Wellknownmethodsincludethelowthroughput[9]sequencingthroughEdmandegradation[10].Moretruehighthroughputproteomictechniquesarebasedonmassspectrometry[11],commonlypeptidemassfingerprinting[12]onsimplerin
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struments,ordenovo[13]sequencingoninstrumentscapableofmorethanoneroundofmassspectrometry.Antibodybasedassayscanalsobeused,butareuniquetooneprotein.
7.Proteinquantification.Gelbasedmethodsareused,includingdifferentialstainingofgelswithfluorescentdyes[14](differencegelelectrophoresis).Gelfreemethodsincludevarioustaggingorchemicalmodificationmethods,suchasisotopecodedaffinitytags(ICATs)[15]orcombinedfractionaldiagnoalchromatography(COFRADIC)[16].
8.Proteinsequenceanalysis.Thisismoreofabioinformaticbranch,dedicatedtosearchingdatabasesforpossibleproteinorpeptidematches,butalsofunctionalassignmentofdomains[17],predictionoffunctionfromsequence,andevolutionaryrelationshipsofproteins.
9.Structuralproteomics.Thisconcernsthehighthroughputdeterminationofproteinstructuresinthreedimensionalspace.Commonmethodsarexraycrystallography[18]
andNMRspectroscopy[19].10.Interactionproteomics.Thisconcernstheinvestigationofproteininteractionsontheatomic,molecularandcellularlevels
11.Proteinmodification.Almostallproteinsaremodifiedfromtheirpuretranslatedaminoacidsequence,socalledposttranslationalmodification[20].Specializedmethodshavebeendevelopedtostudyphosporylation(phosphoproteomics[21])andglycosylation(glycoproteomics[22]).
Keytechnologiesusedinproteomics12.Oneandtwodimensionalgelelectrophoresisareusedtoidentifytherelativemassofa
proteinanditsisoelectricpoint[23].13.Xraycrystallographyandnuclearmagneticresonanceareusedtocharacterizethethree
dimensionalstructureofpeptidesandproteins.14.Tandemmassspectrometry[24]combinedwithreversephasechromatography[25]or2Delectrophoresis[26]isusedtoidentifyandquantifyallthelevelsofproteinsfoundincells.
15.Affinitychromatography[27],yeasttwohybridtechniques[28],fluorescenceresonanceenergytransfer(FRET)[29],andSurfacePlasmonResonance[30](SPR)areusedtoidentifyproteinproteinandproteinDNAbindingreactions.
ProteindatabasesPIR,SwissProt,Pfam,ProteinDataBank
Notes
[1]proteomics[pr[uti5[umiks]n.蛋 白
组学
[2]analogy[[5nAl[dVi]n.类似,类推
[3]entity[5entiti]n.实体
135
[4]radically[5rAdik[li]adv.根本上,以
激进的方式
[5]alternativesplicing[5splaisiN]n.选
择性剪切
[6]posttranslationalmodificationofprotein翻译后蛋白质修饰
[7]catalogue[5kAt[lCg]vt.编制目录
[8]ascertain[7AsE5tein]vt.确定,探知
[9]lowthroughputadj.低通量的
[10]Edmandegradationn.艾德曼降解法
[11]massspectrometry[spek5trRmitri]n.质谱
[12]peptidemassfingerprinting肽 质 量 指
纹图谱
[13]denovo[di:n[Uv[u]adj.从头的
[14]fluorescent[flU[5res[nt]dyen.荧光
染料
[15]isotopecodedaffinitytags(ICATs)[5ais[ut[up5k[Udid[5finititAgs]同
位素被编码的亲和力标记
[16]combinedfractionaldiagnoalchromatography[7kr[Um[5tRgr[fi](COFRADIC)联 合 分 数 对 角 色 谱 法。用
分选标记 肽 段 来 达 到 鉴 定 的 目 的。用
于蛋白质后翻译后修饰分析,已经被应
用于 甲 硫 氨 酸肽 段、半 胱 氨 酸肽 段、蛋白质 N末 端 肽 段、18O标 记 的 C末
端分选。[17]functionalassignmentofdomainn.结
构域功能指派
[18]xraycrystallography[krist[5lRgr[fi]
n.X射线晶体学
[19]NMRspectroscopyn.核 磁 共 振(NuclearMagneticResonance)谱
[20]posttranslationalmodificationn.翻译
后修饰
[21]phosphoproteomics [fRsf[pr[uti5[umiks]n.磷酸蛋白组学
[22]glycoproteomics [glaik[Upr[uti5[umiks]n.糖蛋白组学
[23]isoelectric point [7ais[Ui5lektrikpRint]n.等电点
[24]Tandemmassspectrometryn.串联质
谱
[25]reversephasechromatographyn.反相
层析
[26]2Delectrophoresis[i9lektr[f[5ri:sis]
n.双向电泳
[27]affinitychromatographyn.亲和层析
[28]yeasttwohybridtechniquen.酵母双
杂交技术
[29]fluorescenceresonanceenergytransfer(FRET)n.荧光共振能量转移
[30]SurfacePlasmon[5plAz7m[n]Resonance(SPR)表 面 等 离 谐 振。一 种 基
于物理光学原理的新型生化分析系统,
SPR技术作为一种表在反应 的 生 物 传
感技术,具 有 很 重 要 的 生 化 分 析 能 力,可用于无 标 记 实 时 监 测 许 多 种 类 生 物
分子之间的反应。
136
犝犖犐犜14 犅犐犗犐犖犉犗犚犕犃犜犐犆犛
犈狊狊犪狔50 犅犻狅犻狀犳狅狉犿犪狋犻犮狊,狋犺犲犅犪狊犻犮狊
1.Bioinformatics[1]andcomputationalbiology[2]involvetheuseoftechniquesincludingap
pliedmathematics,informatics[3],statistics,computerscience,artificialintelligence,
chemistryandbiochemistrytosolvebiologicalproblemsusuallyonthemolecularlevel.Researchincomputationalbiologyoftenoverlapswithsystembiology[4].Majorresearcheffortsinthefieldincludesequencealignment[5],genefinding[6],genomeassembly[7],proteinstructurealignment[8],proteinstructureprediction,predictionofgeneexpressionandproteinproteininteractions,andthemodelingofevolution[9].
2.Thetermsbioinformaticsandcomputationalbiologyareoftenusedinterchangeably.Howeverbioinformaticsmoreproperlyreferstothecreationandadvancementofalgorithms[10],computationalandstatisticaltechniques,andtheorytosolveformaland
practicalproblemsposedbyorinspiredfromthemanagementandanalysisofbiologicaldata.Computationalbiology,ontheotherhand,referstohypothesisdriveninvestigationofaspecificbiologicalproblemusingcomputers,carriedoutwithexperimentalandsimulateddata,withtheprimarygoalofdiscoveryandtheadvancementofbiologicalknowledge.AsimilardistinctionismadebyNationalInstitutesofHealthintheirworkingdefinitions[11]ofBioinformaticsandComputationalBiology,whereitisfurtherem
phasizedthatthereisatightcouplingofdevelopmentsandknowledgebetweenthemorehypothesisdrivenresearchincomputationalbiologyandtechniquedrivenresearchinbioinformatics.Computationalbiologyalsoincludeslesserknownbutequallyimportantsubdisciplines[12]suchascomputationalbiochemistryandcomputationalbiophysics.
3.Acommonthreadinprojectsinbioinformaticsandcomputationalbiologyistheuseofmathematicaltoolstoextractusefulinformationfromdataproducedbyhighthroughputbiologicaltechniquessuchasgenomesequencing.Arepresentativeprobleminbioinformaticsistheassemblyofhighqualitygenomesequencesfromfragmentary“shotgun”
DNAsequencing[13].Othercommonproblemsincludethestudyofgeneregulationusingdatafrommicroarrays[14]ormassspectrometry.
MajorResearchAreasofBioinformaticsSequenceanalysis4.SincethePhageΦX174wassequencedin1977,theDNAsequencesofhundredsofor
137
ganismshavebeendecodedandstoredindatabases.Thesedataareanalyzedtodeterminegenesthatcodeforproteins,aswellasregulatorysequences.Acomparisonof
geneswithinaspeciesorbetweendifferentspeciescanshowsimilaritiesbetweenproteinfunctions,orrelationsbetweenspecies(theuseofmolecularsystematicstoconstruct
phylogenetictrees).Withthegrowingamountofdata,itlongagobecameimpracticaltoanalyzeDNAsequencesmanually.Today,computerprogramsareusedtosearchthe
genomeofthousandsoforganisms,containingbillionsofnucleotides.Theseprogramscancompensateformutations(exchanged,deletedorinsertedbases)intheDNAse
quence,inordertoidentifysequencesthatarerelated,butnotidentical.Avariantofthissequencealignmentisusedinthesequencingprocessitself.Thesocalledshotgunsequencingtechnique(whichwasused,forexample,byTheInstituteforGenomicResearchtosequencethefirstbacterialgenome,Haemophilusinfluenza)doesnotgiveasequentiallistofnucleotides,butinsteadthesequencesofthousandsofsmallDNAfragments(eachabout600~800nucleotideslong).Theendsofthesefragmentsoverlapand,whenalignedintherightway,makeupthecompletegenome.Shotgunse
quencingyieldssequencedataquickly,butthetaskofassemblingthefragmentscanbe
quitecomplicatedforlargergenomes.InthecaseoftheHumanGenomeProject,ittookseveralmonthsofCPUtime[15]toassemblethefragments.Shotgunsequencingisthemethodofchoiceforvirtuallyallgenomessequencedtoday,andgenomeassemblyalgorithmsareacriticalareaofbioinformaticsresearch.
5.Anotheraspectofbioinformaticsinsequenceanalysisistheautomaticsearchforgenesandregulatorysequenceswithinagenome.Notallofthenucleotideswithinagenomearegenes.Withinthegenomeofhigherorganisms,largepartsoftheDNAdonotserveanyobviouspurpose.ThissocalledjunkDNA[16]may,however,containunrecognizedfunctionalelements.Bioinformaticshelpstobridgethegapbetweengenomeandproteomeprojects—forexample,intheuseofDNAsequencesforproteinidentification.
Genomeannotation[17]
6.Inthecontextofgenomics,annotationistheprocessofmarkingthegenesandotherbiologicalfeaturesinaDNAsequence.Thefirstgenomeannotationsoftwaresystemwasdesignedin1995byOwenWhite,whowaspartoftheteamthatsequencedandanalyzedthefirstgenomeofafreelivingorganismtobedecoded,thebacteriumHaemophilusinfluenzae.Dr.Whitebuiltasoftwaresystemtofindthegenes(placesintheDNAse
quencethatencodeaprotein),thetransferRNA,andotherfeatures,andtomakeinitialassignmentsoffunctiontothosegenes.Mostcurrentgenomeannotationsystemsworksimilarly,buttheprogramsavailableforanalysisofgenomicDNAareconstantlychangingandimproving.
Computationalevolutionarybiology7.Evolutionarybiologyisthestudyoftheoriginanddescentofspecies,aswellastheir
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changeovertime.Informaticshasassistedevolutionarybiologistsinseveralkeyways;
ithasenabledresearcherstotracetheevolutionofalargenumberoforganismsbymeasuringchangesintheirDNA,ratherthanthroughphysicaltaxonomy[18]orphysiologicalobservationsalone,morerecently,compareentiregenomes,whichpermitsthestudyofmorecomplexevolutionaryevents,suchasgeneduplication[19],lateralgenetransfer[20],andthepredictionofbacterialspeciation[21]factors,buildcomplexcomputationalmodelsofpopulationstopredicttheoutcomeofthesystemovertimetrackandshareinformationonanincreasinglylargenumberofspeciesandorganisms
Futureworkendeavourstoreconstructthenowmorecomplextreeoflife[22]
8.Theareaofresearchwithincomputersciencethatusesgeneticalgorithms[23]issometimesconfusedwithcomputationalevolutionarybiology,butthetwoareasareunrelated.
Measuringbiodiversity9.Biodiversityofanecosystemmightbedefinedasthetotalgenomiccomplementofaparticularenvironment,fromallofthespeciespresent,whetheritisabiofilm[24]inanabandonedmine,adropofseawater,ascoopofsoil,ortheentirebiosphereoftheplanetEarth.Databasesareusedtocollectthespeciesnames,descriptions,distributions,
geneticinformation,statusandsizeofpopulations,habitatneeds,andhoweachorganisminteractswithotherspecies.Specializedsoftwareprogramsareusedtofind,visualize,andanalyzetheinformation,andmostimportantly,communicateittootherpeo
ple.Computersimulatesmodelsuchthingsaspopulationdynamics,orcalculatethecumulativegenetichealthofabreedingpool[25](inagriculture)orendangeredpopulation(inconservation).OneveryexcitingpotentialofthisfieldisthatentireDNAse
quences,orgenomesofendangeredspeciescanbepreserved,allowingtheresultsofNature’sgeneticexperimenttoberememberedinsilico[26],andpossiblyreusedinthefuture,evenifthatspeciesiseventuallylost.
Analysisofgeneexpression10.TheexpressionofmanygenescanbedeterminedbymeasuringmRNAlevelswithmulti
pletechniquesincludingmicroarrays,expressedcDNAsequencetag(EST)[27]sequencing,serialanalysisofgeneexpression(SAGE)[28]tagsequencing,massivelyparallelsignaturesequencing(MPSS)[29],orvariousapplicationsofmultiplexedinsituhybridization[30].Allofthesetechniquesareextremelynoiseprone[31]and/orsubjecttobiasinthebiologicalmeasurement,andamajorresearchareaincomputationalbiologyinvolvesdevelopingstatisticaltoolstoseparatesignalfromnoiseinhighthroughputgeneexpressionstudies.Suchstudiesareoftenusedtodeterminethegenesimplicatedinadisorder:onemightcomparemicroarraydatafromcancerousepithelialcellstodatafromnoncancerouscellstodeterminethetranscriptsthatareupregulated[32]anddownregu
139
lated[33]inaparticularpopulationofcancercells.
Analysisofregulation11.Regulationisthecomplexorchestration[34]ofeventsstartingwithanextracellularsig
nalandultimatelyleadingtoanincreaseordecreaseintheactivityofoneormoreproteinmolecules.Bioinformaticstechniqueshavebeenappliedtoexplorevariousstepsinthisprocess.Forexample,promoteranalysis[35]involvestheelucidationandstudyofsequencemotifs[36]inthegenomicregionsurroundingthecodingregionofagene.ThesemotifsinfluencetheextenttowhichthatregionistranscribedintomRNA.Expressiondatacanbeusedtoinfergeneregulation:onemightcomparemicroarraydatafromawidevarietyofstatesofanorganismtoformhypothesesaboutthegenesinvolvedineachstate.Inasinglecellorganism,onemightcomparestagesofthecellcycle,alongwithvariousstressconditions(heatshock[37],starvation,etc.).Onecanthenapplyclusteringalgorithms[38]tothatexpressiondatatodeterminewhichgenesarecoex
pressed[39].Forexample,theupstreamregions(promoters)ofcoexpressedgenescanbesearchedforoverrepresented[40]regulatoryelements.
Analysisofproteinexpression12.Proteinmicroarraysandhighthroughput(HT)massspectrometry(MS)canprovideasnapshotoftheproteinspresentinabiologicalsample.BioinformaticsisverymuchinvolvedinmakingsenseofproteinmicroarrayandHT MSdata;theformerapproachfacessimilarproblemsaswithmicroarraystargetedatmRNA,thelatterinvolvesthe
problemofmatchinglargeamountsofmassdataagainstpredictedmassesfromproteinsequencedatabases,andthecomplicatedstatisticalanalysisofsampleswheremultiple,
butincompletepeptidesfromeachproteinaredetected.
Analysisofmutationsincancer13.Massivesequencingeffortsarecurrentlyunderwaytoidentifypointmutations[41]inavarietyofgenesincancer.Thesheervolumeofdataproducedrequiresautomatedsystemstoreadsequencedata,andtocomparethesequencingresultstotheknownsequenceofthehumangenome,includingknowngermlinepolymorphisms[42].
14.Oligonucleotidemicroarrays,includingcomparativegenomichybridizationandsinglenucleotidepolymorphism[43]arrays,abletoprobesimultaneouslyuptoseveralhundredthousandsitesthroughoutthegenomearebeingusedtoidentifychromosomalgainsandlossesincancer.HiddenMarkovmodel[44]andchangepointanalysismethodsarebeingdevelopedtoinferrealcopynumberchangesfromoftennoisydata.Furtherinformaticsapproachesarebeingdevelopedtounderstandtheimplicationsoflesions[45]foundtoberecurrent[46]acrossmanytumors.
15.Somemoderntools(e.g.,Quantum3.1)providetoolforchangingtheproteinsequenceatspecificsitesthroughalterationstoitsaminoacidsandpredictchangesinthe
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140
bioactivityaftermutations.
Predictionofproteinstructure16.Proteinstructurepredictionisanotherimportantapplicationofbioinformatics.Theami
noacidsequenceofaprotein,thesocalledprimarystructure[47],canbeeasilydeterminedfromthesequenceonthegenethatcodesforit.Inthevastmajorityofcases,this
primarystructureuniquelydeterminesastructureinitsnativeenvironment.(Ofcourse,thereareexceptions,suchasthebovinespongiformencephalopathy[48]—aka[49]
MadCowDisease[50]—prion).Knowledgeofthisstructureisvitalinunderstandingthefunctionoftheprotein.Forlackofbetterterms,structuralinformationisusuallyclassifiedasoneofsecondary,tertiaryandquaternarystructure[51].Aviablegeneralsolutiontosuchpredictionsremainsanopenproblem.Asofnow,mosteffortshavebeendirectedtowardsheuristics[52]thatworkmostofthetime.
17.Oneofthekeyideasinbioinformaticsisthenotionofhomology[53].Inthegenomicbranchofbioinformatics,homologyisusedtopredictthefunctionofagene:ifthese
quenceofgeneA,whosefunctionisknown,ishomologoustothesequenceofgeneB,
whosefunctionisunknown,onecouldinferthatBmayshareA’sfunction.Inthestructuralbranchofbioinformatics,homologyisusedtodeterminewhichpartsofaproteinareimportantinstructureformationandinteractionwithotherproteins.Inatechniquecalledhomologymodelling[54],thisinformationisusedtopredictthestructureofaproteinoncethestructureofahomologousproteinisknown.Thiscurrentlyremainstheonlywaytopredictproteinstructuresreliably.
18.Oneexampleofthisisthesimilarproteinhomologybetweenhemoglobininhumansandthehemoglobininlegumes(leghemoglobin[55]).Bothservethesamepurposeoftrans
portingoxygenintheorganism.Thoughbothoftheseproteinshavecompletelydifferentaminoacidsequences,theirproteinstructuresarevirtuallyidentical,whichreflectstheirnearidenticalpurposes.
19.Othertechniquesforpredictingproteinstructureincludeproteinthreading[56]anddenovophysicsbasedmodeling.
Comparativegenomics20.Thecoreofcomparativegenomeanalysisistheestablishmentofthecorrespondencebetweengenes(orthologyanalysis[57])orothergenomicfeaturesindifferentorganisms.Itistheseintergenomic[58]mapsthatmakeitpossibletotracetheevolutionaryprocessesresponsibleforthedivergence[59]oftwogenomes.A multitudeofevolutionaryeventsactingatvariousorganizationallevelsshapesgenomeevolution.Atthelowestlevel,
pointmutationsaffectindividualnucleotides.Atahigherlevel,largechromosomalsegmentsundergoduplication,lateraltransfer,inversion[60],transposition,deletionandinsertion.Ultimately,wholegenomesareinvolvedinprocessesofhybridization,
polyploidization[61]andendosymbiosis[62],oftenleadingtorapidspeciation[63].Thecom
141
plexityofgenomeevolutionposesmanyexcitingchallengestodevelopersofmathematicalmodelsandalgorithms,whohaverecoursetoaspectraofalgorithmic,statisticalandmathematicaltechniques,rangingfromexact,heuristics,fixedparameterandapproximationalgorithmsforproblemsbasedonparsimony[64]modelstoMarkovChainMonteCarloalgorithmsforBayesiananalysisofproblemsbasedonprobabilisticmodels[65].Manyofthesestudiesarebasedonthehomologydetectionandproteinfamilycomputation.
Modelingbiologicalsystems21.Systemsbiologyinvolvestheuseofcomputersimulationsofcellularsubsystems[66](suchasthenetworksofmetabolitesandenzymeswhichcomprisemetabolism,signaltransductionpathways[67]andgeneregulatorynetworks)tobothanalyzeandvisualizethecomplexconnectionsofthesecellularprocesses.Artificiallifeorvirtualevolution[68]attemptstounderstandevolutionaryprocessesviathecomputersimulationofsimple(artificial)lifeforms.
Highthroughputimageanalysis22.Computationaltechnologiesareusedtoaccelerateorfullyautomatetheprocessing,
quantificationandanalysisoflargeamountsofhighinformationcontentbiomedicalimagery.Modernimageanalysissystemsaugmentanobserver’sabilitytomakemeasurementsfromalargeorcomplexsetofimages,byimprovingaccuracy,objectivity[69],orspeed.Afullydevelopedanalysissystem maycompletelyreplacetheobserver.Althoughthesesystemsarenotuniquetobiomedicalimagery,biomedicalimagingisbecomingmoreimportantforbothdiagnostics[70]andresearch.Someexamplesare:highthroughputandhighfidelityquantificationandsubcellularlocalization(highcontentscreening,cytohistopathology[71]),morphometrics[72],clinicalimageanalysisandvisualization,determiningtherealtime[73]airflowpatternsinbreathinglungsoflivinganimals,quantifyingocclusion[74]sizeinrealtimeimageryfromthedevelopmentofandrecoveryduringarterialinjury,makingbehaviouralobservationsfromextendedvideorecordingsoflaboratoryanimals,infraredmeasurementsformetabolicactivitydetermination.
Softwaretools23.Firstgenerationbioinformaticstoolsconsistedofapplications,usuallywithatextbasedinterface,whichperformedaspecifictaskwell.ThecomputationalbiologytoolbestknownamongbiologistsisprobablyBLAST[75],analgorithmforsearchinglargedatabasesofproteinorDNAsequences.TheNCBI[76]providesapopularwebbasedimplementationthatsearchestheirmassivesequencedatabases.Alsofairlyearlyon,duetotheamassingofsequenceandannotationdata,keywordsearchengineswhichwereabletoresolvegeneandproteinsynonymswereimportant.Intheseearlydays,computer
UNIT14 犅犐犗犐犖犉犗犚犕犃犜犐犆犛
142
scripting[77]languagessuchasPerlandPythonwereoftenusedtointerfacewithbiologicaldatabasesandparse[78]outputfrombioinformaticsprogramswritteninlanguagessuchasCorC++,andmuchlegacycode[79]isstillinusetoday.Today,manyotherlanguagesareusedtoauthor[80]excellentsoftware,andcommunitiesofbioinformaticsprogrammershavesetupfreeopensourcebioinformaticsprojectstodevelopanddistributethetoolsandmodules[81]theyproduce.
24.Asthedatasourcesexpandedanddiversified,bothincontentandgeography,bioinformaticmetasearchengines[82],suchasSequenceprofilingtools[83],emergedtohelpfindrelevantinformationfromseveraldatabases.Thesemetasearchenginesmightindexdatafromalocalserverorevenfromapanelofthirdpartyservices.
25.Morerecently,SOAP[84]basedinterfaceshavebeendevelopedforawidevarietyofbioinformaticsapplicationsallowinganapplicationrunningononecomputerinonepartoftheworldtousealgorithms,dataandcomputingresourcesonserversinotherpartsoftheworld.AlargeavailabilityoftheseSOAPbasedbioinformaticswebservices,alongwiththeopensourcebioinformaticscollections,leadtothenextgenerationofbioinformaticstools:theintegratedbioinformaticsplatform.Thesetoolsrangefromacollectionofstandalonetoolswithacommondataformatunderasingle,slickstandaloneorwebbasedinterface,tointegrative[85]andextensible[86]bioinformaticsworkflowdevelopmentenvironments.
26.AninterestingnoveldirectionforbioinformaticsapplicationsisillustratedbyQPharm’
sQuantum3.1,anexampleofthebioinformaticspostQSAR[87]technologyapplyingquantumandmolecularphysicsinsteadofstatisticalmethods.
Notes
[1]bioinformaticsn.生物信息学
[2]computational[7kRmpjU:5teiF[n[l]
biology计算生物学
[3]informatics[7inf[5mAtiks]n.信息学
[4]systembiologyn.系统生物学
[5]sequencealignment[[5lainm[nt]n.序列比对
[6]genefindingn.基因识别
[7]genomeassemblyn.基因组(序列)装
配
[8]proteinstructurealignmentn.蛋白质
结构比对
[9]modelingofevolutionn.进化建模
[10]algorithm [5Alg[riT[m]n.运 算 法
则,算法
[11]workingdefinitionn.使用定义
[12]subdiscipline[5sQb5disipliN]n.分支
学科
[13]shotgun[5FQtgQn]DNAsequencingn.鸟枪法DNA测序
[14]microarrayn.微阵列
[15]CPUtimen.中 央 处 理 器 时 间(centralprocessingunittime)
[16]junkDNAn.垃圾DNA[17]genomeannotation [9An[J5teiFLn]
n.基因组注释
[18]physicaltaxonomyn.自然分类法
[19]geneduplication[7djU:pli5keiF[n]n.
143
基因重复
[20]lateralgenetransfer侧向基因转移
[21]speciation[7spi:Fi5eiF[n]n.物种形
成
[22]treeoflife生命之树(进化树)[23]geneticalgorithms遗传算法
[24]biofilm[5bai[film]n.细菌生物被膜,
又称菌膜(bacterialbiofilm),是单一或
多种细菌在不利于其生长的环境下,产生藻酸盐多糖使细菌相 互 粘 连 形 成 膜
状物附于病灶 的 表 面 或 导 管 内。这 是
细菌为适应环境维持自 身 生 命 所 发 生
的形态学的变化,从而增强了细菌对外
环境的抵抗力。这 也 成 为 一 些 细 菌 对
抗生素产生广 泛 耐 药 的 重 要 原 因。临
床上许多顽固性,难治性感染可能均与
形成细菌生物被膜有关。[25]breedingpooln.繁殖种群
[26]insilico[insilik[u]adv.在芯片上
[27]expressedcDNAsequencetag(EST)
n.表达cDNA序列标签
[28]serialanalysisofgeneexpression(SAGE)n.基因表达连续分析
[29]massivelyparallelsignaturesequencing(MPSS)n.大规模平行指纹测序
[30]multiplexedinsitu[in5saitju:]hybridizationn.多元原位杂交
[31]noiseproneadj.易产生噪音的
[32]upregulatedadj.上调的(活性增高)[33]downregulatedadj.下 调 的(活 性 降
低)[34]orchestration[C:kis5treiFn]n.和 谐
的结合,管弦乐作曲法
[35]promoteranalysisn.启动子分析
[36]sequencemotifsn.序列模序
[37]heatshockn.热休克,热激
[38]clusteringalgorithmsn.聚 类 分 析 运
算法则
[39]coexpressv.共表达
[40]overrepresentedadj.超过比例的
[41]pointmutationsn.点突变
[42]germlinepolymorphismsn.种 质 资 源
多态性
[43]singlenucleotidepolymorphismn.单
核苷酸多态性
[44]HiddenMarkovModel(HMM)n.隐
马尔可夫模型
[45]lesion[5li:V[n]n.损伤
[46]recurrent[ri5kQr[nt]adj.再发生的,
周期性发生的,循环的
[47]primarystructuren.一级结构
[48]bovinespongiformencephalopathyn.牛绵状脑
[49]aka亦称(alsoknownas的缩写)[50]MadCowDiseasen.疯牛病
[51]secondary,tertiary,quaternarystructuren.二、三、四级结构
[52]heuristics[hju[5ristiks]n.启发式 方
法
[53]homology[hC5mCl[dVi]n.同源性
[54]homologymodellingn.同 源 建 模,即
利用实验确定的蛋白质 结 构 为 模 板 来
预测另一种具有相似氨 基 酸 序 列 的 蛋
白质(靶)的构象。[55]leghemoglobin[7leghi:m[5gl[Ubin]
n.豆血红蛋白
[56]proteinthreading蛋白质穿针引线法
[57]orthology[5R:WCl[dVi]analysisn.直系同源分析
[58]intergenomic [in5t[:dVi5n[umik]
adj.基因组间的
[69]divergence[dai5v…dV[ns]n.趋异进
化
[60]inversion[in5v[:F[n]n.(遗传)倒位
[61]polyploidization [pRli9plRidai5zeiF[n]n.(遗传)多倍体化
[62]endosymbiosis[5end[J9simbai5[Jsis]
n.内共生
[63]rapidspeciationn.快速物种形成
[64]parsimony[5pB:sim[ni]modelsn.简
UNIT14 犅犐犗犐犖犉犗犚犕犃犜犐犆犛
144
约模型
[65]probabilistic[7prRb[bi5listik]modelsn.概率模型
[66]cellularsubsystemsn.细胞亚系统
[67]signaltransductionpathwaysn.信 号
转导模型
[68]virtualevolution虚拟进化
[69]objectivity[9RbdVek5tiviti]n.客 观
性
[70]diagnostics[7dai[g5nCstiks]n.诊 断
学
[71]cytohistopathology [7sait[u7hist[Up[5WC:l[dVi]n.细胞组织病理学
[72]morphometrics[9mC:f[J5metriks]n.[用作单或复](尤指生物体的)形态测
定,形态特征
[73]realtimeadj.实时的
[74]occlusion[[5klU:V[n]n.梗塞,通道
或脉管的阻塞或闭合
[75]BLASTn.局 部 相 似 性 基 本 查 询 工 具
(BasicLocalAlignmentSearchTool)[76]NCBIn.美国国家生物技术信息 中 心
(网站)(NationalCenterForBiotechnolgyInformation)
[77]computerscriptinglanguagesn.计 算
机脚本语言
[78]parse[pB:z]vt.解析
[79]legacycode[5leg[sik[ud]n.遗产代
码
[80]authorvt.创造,写作
[81]module[5mCdju:l]n.模块
[82]metasearchenginesn.多元搜索引擎
(是在前述搜索引擎基础上建立的可以
同时查 询 多 个 搜 索 引 擎 的 WWW 站
点)[83]Sequenceprofilingtoolsn.序 列 作 图
工具
[84]SOAPn.符号最优汇编程序(SymbolicOptimal[Optimum]AssemblyProgram)
[85]integrative[5intigreitiv]adj.综 合
的,一体化的
[86]extensible[ik5stensibl]adj.可 展 开
的,可扩张的,可延长的
[87]QSARn.(一 种 使 用 广 泛 的 药 物 设 计
方 法)定 量 构 效 方 法 (quantitativestructureactivityrelationship)
145
附录1 生物专业英语常见词素
一、表示数量的词素
1.haplo,mono,uni单,一,独 :haploid单倍体 monoxide一氧化物 monoatomic单原子的
2.bi,di,dipl,twi,du二,双,两,偶:bicolor双色dichromatic双色的diplobacillus双杆
菌dikaryon双核体twin孪生dual双重的
3.tri三,丙:triangle三角triacylglycerol三酰甘油tricarboxylicacidcycle三羧酸循环
4.quadri,quadru,quart,tetr,tetra四:quadrilateral四边的quadrivalent四价的quadru
ped四足动物tetrode四极管tetracycline四环素
5.pent,penta,quique五:pentose戊 糖pentagon五 角 形pentane戊 烷quintuple五 倍 的
pentamer五聚体
6.hex,hexa,sex六:hexose己糖hexapod六足动物hexapoda昆虫纲hexamer六聚体
7.hepta,sept(i)七:heptane庚烷heptose庚糖heptoglobin七珠蛋白
8.oct八:octpus章鱼octagon八角形octane辛烷octose辛糖
9.enne,nona九:nonapeptide九肽enneahedron九面体
10.deca,deka十:decapod十足目动物decahedron十面体decagram 十克
11.hecto百:hectometer百米hectoliter百升hectowatt百瓦
12.kilo千:kilodalton(kD)千道尔顿kilobase千碱基kiloelectronvolt千电子伏特
13.deci十分之一,分:decimeter分米decigram十分之一克
14.centi百分之一:centimeter厘米centimorgan厘摩
15.milli千分之一,毫:millimole毫摩尔 milliliter毫升
16.micro百万分之一,微,微小,微量:microgram微克 microorganism 微生物 microecology微生态学 micropipette微量移液器
17.nano十亿分之一,毫微,纳:nanosecond十亿分之一秒nanometer纳米
18.demi,hemi,semi半:demibarrel半桶hemicerebrum大脑半球semiopaque半透明semi
allele半等位基因semiconductor半导体
19.holo全,整体,完全:holoenzyme全酶holoprotein全蛋白holocrine全(浆分)泌的
20.mega巨大,兆,百万:megaspore大孢子,megabase兆碱基megakaryocyte巨核细胞meg
avolt兆伏 megalopolitan特大城市
21.macro大,巨大,多:macrophage巨噬细胞 macrogamete大配子 macroelement大量元 素
macromolecular大分子的
22.poly,multi,mult多,复合:polyacrylate聚丙烯酸酯polymerase聚合酶 multichain多链
的multinucleate多核的 multicistronicmRNA多顺反子mRNAmulticopy多拷贝
附录1 生物专业英语常见词素
146
二、表示颜色的词素
1.chrom颜色
chromophore生色团chromosome染色体chromatography色谱法
2.melan,melano,nigr黑
melanoma黑素瘤melanin黑色素melanophore黑色素细胞
3.xantho,flavo,fla,flavi,lute黄
xanthophyll叶黄素 xanthous黄 色 的,黄 色 人 种 xanthine黄 嘌 呤flavin(e)黄 素flavone黄酮lutein黄体素flavinadeninedinucleotide(FAD)黄素腺嘌呤二核苷酸
4.erythro,rub,rubrm,ruf红
erythrocyte红细胞erythromycin红霉素erythropoietin(EPO)促红细胞生成素
5.chloro,chlor绿,氯
chlorophyll叶绿素chloride氯化物chloramphenicol氯霉素
6.cyan,cyano蓝,青紫色,氰
cyanophyceae蓝藻纲cyanobacteria蓝细菌cyanide氰化物
7.aur,glid,chrys金色
aureomycin金霉素chrysose金藻淀粉chrysanthemum菊花gild镀金
8.leu,leuco,leuk,leuko,blan,alb无色,白色
leucine亮氨酸leukaemia=leucosis白血病bleachingpowder漂白粉albomycin白霉素
三、表示摄食的词素
1.vore食……动物,vorous食……动物的
algivore食藻动物carnivore食肉动物herbivore食草动物omnivore杂食动物
2.phage吃(食)食……生物(体)phagous吃(食)……的
phage=bacteriophage噬菌体phagocyte吞噬细胞zoophage食肉动物saprophage腐食
者
四、表示方位和程度的词素
1.endo,ento内,在内
endocrine内分泌endocytosis胞 吞 作 用endogamy同 系 交 配endolysin内 溶 素entoderm内胚层
2.ec,ect,exc,extra外,外面,表面
ectoblast外胚层ectoparasite外寄生生物extract抽取,浸出
3.meso中,中间
mesosphere中圈,中层 mesoblast中胚层质
4.intra,intro,inter在内,向内
intraallelicinteraction等位基因内相互作用intracellular(细)胞内的interurban城市之间
147
5.centri,centro,medi,mid中心,中央,中间
centrifuge离心centriole中心粒centrosome中心体centrogene着丝基因
6.epi,peri上,外,旁
epidermalgrowthfactor(EGF)表皮生长因子epibranchial上鳃的perilune近月点
7.sub,suc,suf,sug下,低,小
suborder亚目submucosa黏膜下层subclone亚克隆subcellular亚细胞subsection小节,
分部
8.super,supra上,高,超
superconductor超导体superfluid超流体superoxide超氧化物supramolecular超分子的
9.hyper超过,过多
hypersensitive过敏的hyperelastic超弹性的hypertension高血压hyperploid超倍体
10.hypo下,低,次
hypoglycaemia低血糖hypotension低血压hypophysis脑下垂体
11.iso等,相同,同
isoosmotic等渗的isopod等足目动物isotope同位素
12.oligo,olig少,低,寡,狭
oligohaline狭盐性oligogene寡基因oligomer低聚体oligophagous寡食性oligarchy寡
头政治
13.eury多,宽,广
eurythermal广温的euryhaline广盐性eurytopicspecies地理的、生境的广分布种
14.ultra超
ultraacoustics超声学ultrastructure超微结构ultraviolet紫外线
15.infra下,低,远
infralittoral潮下带,远岸的infrahuman类人生物infrared红外线的infrastructure基础
结构
五、表示动物不同器官和组织的词素
1.cephal,capit,cran头,头颅
2.cyte细胞
3.carn,my,mya,myo肉,肌肉
4.haem,haemat,hem,aem,sangul血
5.soma,corp体,身体
6.some,plast体,颗粒
7.hepa,hepat肝 :heparin肝素hepatopancreas肝胰腺hepatocyte肝细胞hepatoma肝癌
8.ren,nephr肾:adrenal肾上腺的nephridia肾管nephron肾单位
9.card,cord心:cardiotoxin心脏毒素cardiovascularcenter心血管中枢electrocardiogram心电图concord一致,和谐
10.ophthalm,ocell,ocul眼:ophthalmology眼科学ophthalmia眼炎ophthalmologist眼科专
附录1 生物专业英语常见词素
148
家
11.branchi鳃:filibranch丝鳃lamellibranch瓣鳃secondarybranchia次生鳃
12.brac,brachi腕,手臂:brachiolaria短腕幼虫brachionectin臂粘连蛋白bracelet手镯
13.dent,odont牙齿:dentin牙质odontphora齿舌odontoblast成牙质细胞
14.plum羽:plumatus羽状的plumule羽绒plumage(鸟的)羽毛
15.foli,foil叶:follicle滤泡foiling叶形foliage叶子foliose多叶的
149
附录2 生物专业英语常见词缀
表示无,抗,非的前缀
一、a,an无,非。可以进一步理解为离开,除去,脱去等
1.无
abacteria无菌的,atony无力,anemia贫血(无血之意),abiosis无生命,abrachia无臂畸形,
adacrya无泪,adactylia无指(趾)畸形,adendric无树突的,atrophoderma皮肤萎缩(即无皮
肤营养之意),adiaphoresis无汗症。
2.否定
asymmetric不对称的,asynergy不协调,asystole心搏停止(心脏不收缩),atactic共济失调
的(不协调),asynchronous不同步的,asyllabia拼音不能。
3.离开
aspiration吸引,aberrant迷走的(即离开正常途径的)。
4.An在元音前用ananaerobe厌氧菌,anaesthesia无感觉,麻醉,analgesia无痛法,痛觉消失,anamniotic无羊
膜的,anangioplasia血管发育不全,anapepsia胃蛋白酶缺乏,anaplasia退行发育,anascitic无腹水的,anastigmatic无散光的,anacholia胆汁缺乏。
二、ab去,离开,除
abnormal不正常的(即背离正常的),abapical离尖的,离心尖的(尖以外的,心尖外的),abarticular关节外的,abaxial轴外的,离轴的,abduct绑架,外 展,ablactation断 奶(离 开 奶),abneural神经外的。
三、Ant,anti,对抗,取消,抑制,解除
antagonistic对抗 的,antitoxin抗 毒 素,antibody抗 体,antigen抗 原,antacid抗 酸 剂,antipyretic解热剂,antibiotic抗菌素,antispasmin解痉剂,antiamylase抗淀粉酶,anticoagulant抗
凝的。
四、De向下,减少,降低,除去,否定,离开,解除,脱去等
deacidification去酸 作 用,deactivation灭 活 性,deacylase脱 酰 基 酶,deamination脱 氨 作 用,
deaquation脱水 作 用,deviate背 离,decrease减 少,descend下 降,decompose分 解,decompress减压,deficiency不中,不全,缺乏,deceleration减速度,deformity畸形,变形(非正常形
态之意),degeneration退行性变,变性(即背离正常性质),decentration偏心(即离开中心),
附录2 生物专业英语常见词缀
150
decerebrate去大脑decortication去皮质,去皮层,defibrillate除震颤,deficit短缺,deflection偏向,detail详细(de也有表示完全之意)。
五、Dis否定,分开,相反等
disability丧失劳动力,disaggregation感觉综合不能,disassimilation异化作用,dislocation脱
位,disassociation分离,discharge放电,discission挑开术,分裂术,discomfort不舒适disconnect分离,不连接,descrimination辨别(含分开之意),disequilibrium不平衡。
六、Il,im,in,ir非,无,不
1.In非,无,不
inactive无活性的,inability无 能 力,inaccurate不 精 确 的,insoluble不 溶 解 的,inadequate不适当的,inadaptable不适应的,inacidity无酸,inaction无作用,inanimate无生命的,incapacity机能不全,incoagulable不能凝固的,inalimental无营养的。
2.Im为in的变形,在b,p,m,之前用imimpossible不可 能 的,imperforation无 孔,impermeability非 渗 透 性,imbalance不 平 衡,
immature不成熟的,immiscible不可混合的,immobility不活动,impalpable不可触知的,
impotency阳痿(阴茎不能勃起),impure不纯的。
3.Il为in之变形,用于l之前
illhealth健康不佳,illeffect不良作用,illhumor心境不佳,illnourished营养不良的。
4.Ir为in之变形,用于r之前
irregular不规则的,irreversible不可逆的,irreducible不可还原的,不能复归的,不能削减
的,[数]不可约分的,irrespirable不能呼吸的,irresuscitable不可复苏的。
七、Non非,无,不
nonabsorbent非吸收性的,nonacid非酸性的,nonallergic非变态反应性的,nondevelopment不发育,nonconductor非导体,nonimmune非免疫性的,noncongestive非 充 血 性 的,nonmotile无运动的,noninfective非传染性的,非感染性的,nonhemolytic非溶血性的,nonmetal非
金属的,nonsurgical非手术的,非外科的,nonspecific非特异性的,nonviable不能生活的。
八、Un不,非,无
unavoidable不可避免的,unbalance不 平 衡,unknown未 知 的,unconsciousness无 意 识,uncomfortable不舒适的,uncompleted不完全的,uncomplemented未与补体结合的,undifferentiation未分化。
表示数量的前缀
一、基数词
1.uni单一
unilateral单侧的,unipolar单极的,uniaural单耳的,unicentral单中心的,unicellular单细
胞的,unidirectional单向的,unifocal单病灶的,uniocular单眼的,unipara初产妇,unit单
151
位。
2.bi,di,diplo,amb,amphi,ampho,二,双
(1)bibiacuminate有二尖端的,biangulate有两角的,bicarbonate重碳酸盐,biauricular双耳
的,biaxial双轴的,bicavity双腔的,biceps二头肌,biconvex双凸的,bivalent双价的,
bivalve双瓣的。(2)didiacetate双醋酸盐,diacetyldiphenolisatin双 醋 酚 酊,diacid二 酸,diamide二 酰 胺,dihybrid双因子杂种,dihydrochlorothiazide,双 氢 氯 噻 嗪,双 氢 克 尿 塞 (一 种 利 尿 药),
diphosphate双磷酸 盐,diad二 分 体,disome双 染 色 体,disomy双 躯 干 畸 胎,二 体 生
物。(3)diplodiplobacillus双杆菌,diploblastic二胚层的,diplococcus双球菌,diploid二倍体,diploneural双重神经支配的,diplopia复视,diplostreptococcus双链球菌。
(4)ambi,amb,ambo二,两侧,复
ambilateral两侧的,ambiopia复视,ambivalent矛盾情绪的(两方面情绪的),ambisexual两性的。
(5)amphi二,两侧,两端
amphibia两栖类,amphichromatic两性反应的,amphigenesis两性生殖,amphinucleolus双核仁,amphipeptone两性胨。
(6)ampho意同amphiamphochromophil双染性的,amphotericin两性霉素,amphoteric两性的。
3.tri三
triangle三角,triad三联症,triacetate三乙酸盐,triacid三价酸,triage伤员拣别分类(国外
急诊室将伤员进行分类,大批伤员选出,有可能抢救存活的病人,先进行抢救,分出轻重缓
急,以便抢救存活更多的病人,此处无三的含义),trialism 三元论,triamine三胺,triatomic三原子的,tribasic三碱价的,tribromide三溴化物。
4.quadra,quadri,tetra,tetro四
(1)quadra,quadri
quadrant四分体,象 限,quadrate四 方 的,quadratus方 肌,quadriceps四 头 肌,quadricuspid四尖的,quadrigeminum四叠体,quadriplegia四肢瘫。
(2)tetra,tetrotetracycline四环素,tetrachloride四氯化物,tetrachlormethane四氯甲烷,tetralogy四
联症,tetrapeptide四肽。
5.penta,pento五
pentacyclic五环的,pentadactyl五指(趾)的,pentose戊糖,pentanucleotide五核苷酸,pentazole五唑,pentobarbital戊巴比妥。
6.hex,hexa六
hexachlorophene六氯酚,hexad六价元素,hexagonal六角形的,hexahydric六氢的,hexane己烷,hexestrol己雌酚。
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152
7.hept,hepta,sept,七
heptaldehyde庚醛,heptatomic七原子的,七元(价)的,heptavalent七价的,heptose庚糖,
septavalent七价的。
8.octa,octo八
octylacetate辛醋酸酯,octose辛糖,octylene辛烯。
9.nona九
nonan第九日的,nonipara九产妇(第九次生产)。
10.deca十
decacurie十居里(同位素量),decagram 十克,decaliter十升,decameter十米,decanormal十当量的(溶液浓度单位)。
二、数量程度
1.haplo,mono单
(1)haplohaplodermatitis单纯性皮炎,haploid单倍体,haplomycosis单孢子囊菌病,haplopathy无合并症的单纯病,haplopia单视。
(2)monomonocyte单核细胞,mononuclear单核的,mononeuritis单神经炎,monoacid单价酸的,
monoarticular单关节的,monogeny单性生殖,monocelled单细胞的,monoxide一氧化
物,monochromatic单色的,monophase单相。
2.multi,pleo,pluri,poly多
(1)multimultiple多的,multicapsular多 囊 的,multicellular多 细 胞 的,multicenrtric多 中 心 的,
multifetation多胎妊娠,multiform 多 形 的,multilobular多 叶 的,multiparous多 胎 的,
multivalence多价,multiterminal多端的,multinodular多结节的。(2)pleo
pleocaryocyte多核细胞,pleochroic多色的,pleochromocytoma多色细胞瘤,pleocytosis脑脊液细胞增多,pleolysis最大溶血浓度,pleomastia多乳房,pleomorphic多形的。
(3)pluri
pluridyscrinia多种分泌障碍,pluriglandular多腺性的,plurigravida经产的,plurimenorrhea多次行经,plurinuclear多核的,pluripara经产妇,pluripolar多极的,pluripotential多能的。
(4)poly
polycythemia红细胞增多症,polycystic多囊的,polycystoma多囊病,polychylia乳糜过
多,polycylic多 环 的,polyclinic综 合 门 诊 所,综 合 医 院,分 科 医 院,polydipsia烦 渴,
polydontia多牙。
3.demi,hemi,semi半
(1)demidemifacet半面,demilune半月形的,新月细胞。
(2)hemi
153
hemiplegia半身 不 遂,hemiprotein半 蛋 白 质,hemipylorectomy幽 门 部 分 切 除 术,hemiscotosis偏侧 盲,hemisection对 切,hemispasm 偏 侧 痉 挛,hemisphere半 球,hemisyndrome偏侧综合征,hemisynergia偏身协同动作,hemitetany半身手足搐搦,hemitoxin半毒素。
(3)semisemiantigen半抗 原,semicanal半 管,semicircular半 环 形 的,semicoma半 昏 迷,轻 昏
迷,semiconscious半清醒的,semidecussation半交叉,semiflexion半屈,semilunare月
骨,semimembrane半渗透膜的,semiplegia半瘫,semipolar半极的,semirecumbent半
卧的,semitransparent半透明的,semicartilaginous半软骨的。
4.holo,pan,完全
(1)holo全部,完全
holoantigen全抗原,holocephalic头部完整的,holodiastolic全舒张期的,holopathy全
身病,holosteosclerosis全身骨硬化,holosystolic全收缩期的,holotetanus全身性破伤
风,holotonia全身肌紧张。(2)pan完全
panagglutination全凝集,panarthritis全关节炎,panarteritis全动脉炎,panesthesia全
感觉 ,pancarditis全心炎,pancytopenia全血细胞减少,pancytosis全血细胞增多。
5.mero,topo局部
(1)mero常指部分
meromicrosomia部分躯干过小,meropia部分盲,merorachischisis部分脊柱裂,meromorphosis再生不全。
(2)topo常指部位
toponarcosis局部麻醉,toponeurosis局部神经机能病,topoalgia局部痛,topodysesthesia局部感觉迟钝,topographic地形的,topology拓扑学。
6.giga,giganto,megamegalo,macro大,巨大
(1)giga,giganto
gigantism巨人症,gigantoblast巨大有核红细胞,gigantocyte巨大红细胞,gigantosoma巨大发育。
(2)mega,megalomegabacterium巨大细菌,megabladder巨 大 膀 胱,megacardia心 肥 大,megacaryoblast成巨核细胞,megacaryocyte巨核细胞,megacecum巨肓肠,megacephalia巨头,megacolon巨结肠,megalencephalon巨脑,megalerythema巨大红斑,megaloblast巨成红细胞
,megalocardia心肥大,megalocephlia巨头,megalodactyly巨趾(指),megaloesophagus巨食管,megaloglossia巨舌。
(3)macro除巨大外,还指长
macrocephalous巨头的,macrocheilia巨唇,macrocheiria巨手,macrochromosome巨染
色体,macroclitoris巨阴蒂,macrococcus巨型球菌,macrocyst巨囊,macrocyte巨红细
胞,macrobiosis长寿,macrocomous长毛的。
7.hyper,over,ultra.过多,超过
(1)hyper过多,超过,上高,重,过度等
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hypertension高血压病,hyperthyroidism 甲状腺功能 亢 进 症,hyperalimentosis营 养 过
度hypertrophy肥大,hyperchloridation供氯过多,hyperchloride过氯化物,hypercholia胆汁过多,hyperchondroplasia软骨增殖过多,hyperiodemia高碘血症,hyperlethal超致
死的,hypermania重 躁 狂 症,hypernormal超 常 的,hyperendemic发 病 率 高 而 持 续 的,
hyperimmunity超免疫,hypertonic高张的。(2)over过度
overaction作用 过 度,overactive活 动 过 度 的,overalimentation营 养 过 度,overcorrection矫正过度,overgrowth生 长 过 度,overhydration水 分 过 多,overdistension膨 胀 过
度,overexertion用力过度,overlapping重叠,overresponse反应过度。(3)ultra超过
ultracentrifugal超离 心 的,ultrafilter超 滤 器,ultramicron超 微 粒,ultrasonic超 声 波
的,ultraviolet紫外线,ultrasound超声。
8.hypo,micro,oligo,sub少,小,不足
(1)hypo低,少,减退,不足,次,过少,不全
hypoacidity胃酸 过 少,酸 过 少,hypoactivity活 动 减 低,hypoalbuminemia血 白 蛋 白 减
少,hypoalimentation营养不足,hypobaropathy低气压病,hypobilirubinemia低胆红素
血症,hypobromite次 溴 酸 盐(hypo化 学 上 译 为 次),hypocalcification钙 化 不 全,hypocalcia钙不足,hypoevolutism发育迟缓,hypoglycemia低血糖症,hypohidrosis少汗,
hyponoia精神迟钝 。
hypo的有其他含意在此一并讨论:
hypocondylar髁下的,hypoderm皮下组织,hypoglossus舌下神经,hypoglottis舌下部,
hypolarynx喉下部,hypospadias尿道下裂,hypophrenium膈下腔,hypotropia下斜视。(2)micro小,细,微
microscope显微镜,microscopist显微镜工作者,microsecond微秒,microsection显微切
片,microslide显微镜玻片,microsoma微粒体,microsphere微球体,microspherocyte小
球形红细胞 ,microsporangium小孢子囊。(3)oligo少,缺少
oligoamnios羊水过少,oligocardia心动徐缓(心跳次数少),oligocholia胆汁过少,oligochromemia血红蛋白过少,oligocythaemia红细 胞 减 少,oligopnea呼 吸 迟 缓(呼 吸 次 数
少),oligosideremia血铁减少,oligospermia精子减少,oligosteatosis皮脂减少,oliguria少尿。
(4)sub不全,不足,次,亚,下
subacetate次醋酸盐(sub化 学 上 译 为 次),subacidity酸 不 足,subacute亚 急 性,subfebrile微热 的,subinvolution复 旧 不 全,subtotal次 全 的,subconsciousness下 意 识 的,
subdivision亚门,subgroup亚群,subfamily亚科,subiodide次碘化物,sublethal亚致死
的,subleukemia亚白血病。
sub除上述含意外,还表示位置在下面。
subabdominal腹下的,subarachnoid蛛网膜下的,subaural耳下的,subscapular肩胛下
的,subclavicular锁骨下的,substratum下层。