CELULA DEFINITII

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organelle is a specializedsubunit within a cell that has a

specific function exemple:Golgi apparatus sorting andmodification of proteinsmitochondria energyproduction from the oxidationof food substances and therelease of adenosinetriphosphatenucleus DNA maintenance,

controls all activities of thecell, RNA transcription

eukaryote is an organismwhose cells contain complex

structures enclosed withinmembranes. The definingmembrane-bound structure
http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Golgi_apparatushttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Transcription_(genetics)http://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Biological_membranehttp://en.wikipedia.org/wiki/Golgi_apparatushttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Transcription_(genetics)http://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Biological_membranehttp://en.wikipedia.org/wiki/Cell_(biology)


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that sets eukaryotic cellsapart from prokaryotic cells is

the nucleus, or nuclearenvelope, within which thegenetic material is carried.[1][2] [3] The presence of anucleus gives eukaryotes theirname

Ploidy is the number of setsofchromosomes in a

biological cell.Human sex cells (sperm andegg) have one complete set ofchromosomes from the maleor female parent. Sex cells,also called gametes, combineto produce somatic cells.Somatic cells therefore have
http://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Nuclear_envelopehttp://en.wikipedia.org/wiki/Nuclear_envelopehttp://en.wikipedia.org/wiki/Eukaryote#cite_note-Youngson-0http://en.wikipedia.org/wiki/Eukaryote#cite_note-Nelson.26Cox-1http://en.wikipedia.org/wiki/Eukaryote#cite_note-Nelson.26Cox-1http://en.wikipedia.org/wiki/Eukaryote#cite_note-Martin-2http://en.wikipedia.org/wiki/Eukaryote#cite_note-Martin-2http://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Biological_cellhttp://en.wikipedia.org/wiki/Spermhttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Somatic_cellshttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Nuclear_envelopehttp://en.wikipedia.org/wiki/Nuclear_envelopehttp://en.wikipedia.org/wiki/Eukaryote#cite_note-Youngson-0http://en.wikipedia.org/wiki/Eukaryote#cite_note-Nelson.26Cox-1http://en.wikipedia.org/wiki/Eukaryote#cite_note-Martin-2http://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Biological_cellhttp://en.wikipedia.org/wiki/Spermhttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Somatic_cells


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twice as many chromosomes.The haploid number (n) is

the number of chromosomesin a gamete. A somatic cellhas twice that manychromosomes (2n).

Humans are diploid. A humansomatic cell contains 46chromosomes: 2 completehaploid sets, which make up23 homologous chromosome

pairs. However, manyorganisms have more thantwo sets of homologouschromosomes and are calledpolyploid.

prokaryotes are a group oforganisms that lack a cellnucleus (= karyon), or any
http://en.wikipedia.org/wiki/Homologoushttp://en.wikipedia.org/wiki/Polyploidyhttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Homologoushttp://en.wikipedia.org/wiki/Polyploidyhttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleus


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other membrane-boundorganelles. The organisms

that have a cell nucleus arecalled eukaryotes.

DNA Deoxyribonucleic acid

(/diksirab.njukle.ksd/ ( listen)), or DNA, is anucleic acid that contains thegenetic instructions used inthe development and

functioning of all known livingorganisms (with the exceptionofRNA viruses). The main roleof DNA molecules is the long-term storage ofinformation.DNA is often compared to aset ofblueprints, like a recipeor a code, since it contains the
http://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://upload.wikimedia.org/wikipedia/commons/f/f2/En-us-Deoxyribonucleic_acid.ogghttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/RNA_virushttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Blueprinthttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://upload.wikimedia.org/wikipedia/commons/f/f2/En-us-Deoxyribonucleic_acid.ogghttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/RNA_virushttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Blueprint


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instructions needed toconstruct other components

ofcells, such as proteins andRNA molecules. The DNAsegments that carry thisgenetic information are calledgenes, but other DNAsequences have structuralpurposes, or are involved inregulating the use of thisgenetic information.

The nucleotide repeatscontain both the segment ofthe backbone of the molecule,which holds the chain

together, and a base, whichinteracts with the other DNAstrand in the helix. A base
http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Gene


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linked to a sugar is called anucleoside and a base linked

to a sugar and one or morephosphate groups is called anucleotide. If multiplenucleotides are linkedtogether, as in DNA, thispolymer is called apolynucleotide.[9]

The backbone of the DNAstrand is made from

alternating phosphate andsugar residues.[10

O molecul de ADN conine

zone numite gene , zonefr funcie, precum izone cu un rol ncnecunoscut;
http://en.wikipedia.org/wiki/Nucleosidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Polynucleotidehttp://en.wikipedia.org/wiki/DNA#cite_note-IUPAC-8http://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Carbohydratehttp://en.wikipedia.org/wiki/DNA#cite_note-Ghosh-9http://ro.wikipedia.org/wiki/Gen%C4%83http://ro.wikipedia.org/wiki/Gen%C4%83http://en.wikipedia.org/wiki/Nucleosidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Polynucleotidehttp://en.wikipedia.org/wiki/DNA#cite_note-IUPAC-8http://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Carbohydratehttp://en.wikipedia.org/wiki/DNA#cite_note-Ghosh-9http://ro.wikipedia.org/wiki/Gen%C4%83


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ADN-ul este un acid nucleic.Este o polinucleotid, adic un

compus n structura cruia serepet un set limitat demacromolecule numitenucleotide ; n acest sens, eleste definit ca fiind uncopolimer statistic:un copolimer este un

polimer n compoziiacruia se repet mai multe

motive (monomeri); ncazul ADN-ului, monomeriisunt nucleotidele.

iar statistic nseamn cmonomerii se repet de

manier aleatorie n lanulpolimer, fr ca ei s fiedispui alternativ sau dup
http://ro.wikipedia.org/wiki/Acidhttp://ro.wikipedia.org/wiki/Nucleotid%C4%83http://ro.wikipedia.org/wiki/Nucleotid%C4%83http://ro.wikipedia.org/wiki/Polimerhttp://ro.wikipedia.org/wiki/Polimerhttp://ro.wikipedia.org/wiki/Acidhttp://ro.wikipedia.org/wiki/Nucleotid%C4%83http://ro.wikipedia.org/wiki/Polimer


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oricare alt aranjamentrepetitiv (aa cum se

ntmpl, de exemplu, netilen-acetatul de vinil(EVA) sau n acronitril-butadien-stiren (ABS).

Nucleotida, ce reprezintunitatea de baz a ADN-ului,este o macromoleculorganic (o N-glicozid)compus (prin

policondensare) din:un carbohidrat, adic o

glucid (mai exact omonozaharid) de tipulpentoz (n formfuranozic)

o baz azotat heterociclic(inel sau ciclu aromatic
http://ro.wikipedia.org/wiki/Glucid%C4%83http://ro.wikipedia.org/wiki/Glucid%C4%83


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n 6 atomi) de tipulpirimidinei, sau o variant a

acesteia condensat cuinelul imidazolic, numitpurin

i un rest de acid fosforic(esterificat cu unul dinhidroxilii pentozei), adicun grup fosfat.[A]

Pentozele care intr nstructura ADN-ului sunt D-2-

dezoxiriboza (pentru acidulnucleic tip ADN) sau D-riboza(pentru acidul nucleic tipARN).[B] Dou dintre bazeleheterociclice azotate ale ADN-

ului sunt purinice (adenina iguanina), iar celelalte dousunt pirimidinice (citozina i
http://ro.wikipedia.org/wiki/ADN#endnote_Covic.2C_2004.2C_p._19Ahttp://ro.wikipedia.org/wiki/ARNhttp://ro.wikipedia.org/wiki/ADN#endnote_Covic.2C_2004.2C_p._19Bhttp://ro.wikipedia.org/wiki/Adenin%C4%83http://ro.wikipedia.org/wiki/Guanin%C4%83http://ro.wikipedia.org/wiki/Citozin%C4%83http://ro.wikipedia.org/wiki/ADN#endnote_Covic.2C_2004.2C_p._19Ahttp://ro.wikipedia.org/wiki/ARNhttp://ro.wikipedia.org/wiki/ADN#endnote_Covic.2C_2004.2C_p._19Bhttp://ro.wikipedia.org/wiki/Adenin%C4%83http://ro.wikipedia.org/wiki/Guanin%C4%83http://ro.wikipedia.org/wiki/Citozin%C4%83


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timina). n ARN uracilulnlocuiete timina. n cadrul

elicei caracteristice, n formde scar spiralat, resturilepirimidinice ale monomeruluisunt orientate spre interior,formnd cu resturile puriniceale celuilalt monomertreapta scrii, n timp cepentozele formeaz braeleacesteia, de la o dubl unitate

la alta (adic de la un cuplupurinic-pirimidinic laurmtorul), legtura fiindrealizat de gruprile fosfat(prin atomii lor de oxigen).

Legturile dintre resturile depurine i pirimidine sunt denatur molecular i nu
http://ro.wikipedia.org/wiki/Timin%C4%83http://ro.wikipedia.org/wiki/Uracilhttp://ro.wikipedia.org/wiki/Timin%C4%83http://ro.wikipedia.org/wiki/Uracil


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chimic, ele fiind legturi dehidrogen.

Mutaiile nu sunt altcevadect imperfeciuni nprocesul de sintez al ADN-ului: o baz este n mod

accidental ignorat(srit), introdus saucopiat imperfect, saulanul este tiat preadevreme sau i se adaug

baze la capete; acesteoperaii de bazgenereaz toate mutaiileposibile.

Mutaiile genetice suntpractic o alterare a uneipri din informaia dinmolecula ADN. Este


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suficient ca, de exemplu, sse tearg doar o pereche

de baze azotate dintr-ogen, pentru ca toatfuncia genei s fie abolit.Dac este tears opereche de baze azotate,codonul din care fceaparte aceasta va codificaalt aminoacid, care vacodifica alt protein, fapt

ce, n cele din urm (aa sentmpl probabil cel maiadesea, ns nu n modobligatoriu), poate s-ialtereze acesteia din urm

funcia biologic. Mutaiilepot avea trei feluri deefecte: negative, pozitive
http://ro.wikipedia.org/wiki/Gen%C4%83http://ro.wikipedia.org/wiki/Gen%C4%83


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sau neutre (nu influeneazfunciile nici n bine, nici n

ru).Aceste mutaii sunt

provocate fie de aa numiiifactori mutageni (radiaiilecosmice, substane chimice.a.), fie de fidelitateaimperfect a enzimei ceasigura sinteza ADN-ului.

Mutaiile genetice pot fi i

induse intenionat de ctrespecialiti.ADN-ul se gsete practic n

orice celul:de la organisme

unicelulare cum ar fibacteriile sauprotozoarele,


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pn la organismelepluricelulare (fungi,

vegetale sau animale),precum i n structura

intern a unor virusuri.Structura ADN-ului este unic

nu numai pentru o specieanume ci i pentru oriceindivid al oricrei speciianimale sau vegetale.

La om ADN-ul conine circa

3,27 miliarde de perechi debaze (3,27 miliarde detrepte n helixul dublu).

Cantitatea de ADN coninutn celule (numit uneori i

patrimoniu genetic) nu estecorelat cu complexitateaorganismului. Astfel, de
http://ro.wikipedia.org/wiki/Virushttp://ro.wikipedia.org/wiki/Speciehttp://ro.wikipedia.org/wiki/Individhttp://ro.wikipedia.org/wiki/Virushttp://ro.wikipedia.org/wiki/Speciehttp://ro.wikipedia.org/wiki/Individ


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exemplu, exist specii maipuin complexe dect

omul, dar cu un patrimoniugenetic mai bogatcantitativ dect cel alomului.

backbone chain or mainchain of a polymer is theseries ofcovalently bondedatoms that together create

the continuous chain of themolecule.

genes have regulatoryregions in addition to regions

that explicitly code for aprotein or RNA product. Aregulatory region shared by
http://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Regulatory_sequencehttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Regulatory_sequence


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eye or a leg, or repairing awound.

A chromosome contains asingle, long DNA molecule,only a portion of whichcorresponds to a singlegene. Humans haveapproximately 23,000genes arranged on theirchromosomes.Each gene consists of a

specific sequence ofnucleotides encoded in aDNA (or sometimes RNA)strand.genetic code is the set of

rules by which a gene istranslated into a functionalprotein.


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genome is the entirety of anorganism's hereditary

information.

allele is one of two or moreversions of a gene. Anindividual inherits two allelesfor each gene, one from eachparent. If the two alleles arethe same, the individual ishomozygous for that gene. If

the alleles are different, theindividual is heterozygous.Though the term "allele"_ wasoriginally used to describevariation among genes, it now

also refers to variation amongnon-coding DNA sequences.allele (UK /lil/ or US/ li l/)
http://en.wikipedia.org/wiki/Hereditaryhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Hereditaryhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Keyhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_English


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of properties.

Because of the extraordinaryrange of properties ofpolymeric materials,[2] theyplay an essential andubiquitous role in everyday

life.[3] This role ranges fromfamiliar synthetic plastics andelastomers to naturalbiopolymers such as nucleicacids and proteins that are

essential for life.Natural polymeric materialssuch as shellac, amber, andnatural rubber have been

used for centuries. A varietyof other natural polymersexist, such as cellulose, whichis the main constituent of
http://en.wikipedia.org/wiki/Polymers#cite_note-PC1-1http://en.wikipedia.org/wiki/Polymers#cite_note-MBB1-2http://en.wikipedia.org/wiki/Elastomerhttp://en.wikipedia.org/wiki/Biopolymershttp://en.wikipedia.org/wiki/Nucleic_acidshttp://en.wikipedia.org/wiki/Nucleic_acidshttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Natural_polymerhttp://en.wikipedia.org/wiki/Shellachttp://en.wikipedia.org/wiki/Amberhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Cellulosehttp://en.wikipedia.org/wiki/Polymers#cite_note-PC1-1http://en.wikipedia.org/wiki/Polymers#cite_note-MBB1-2http://en.wikipedia.org/wiki/Elastomerhttp://en.wikipedia.org/wiki/Biopolymershttp://en.wikipedia.org/wiki/Nucleic_acidshttp://en.wikipedia.org/wiki/Nucleic_acidshttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Natural_polymerhttp://en.wikipedia.org/wiki/Shellachttp://en.wikipedia.org/wiki/Amberhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Cellulose


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wood and paper. The list ofsynthetic polymers includes

synthetic rubber, Bakelite,neoprene, nylon, PVC,polystyrene, polyethylene,polypropylene,polyacrylonitrile, PVB, silicone,and many more.Most commonly, thecontinuously linked backboneof a polymer used for the

preparation of plasticsconsists mainly ofcarbonatoms. A simple example ispolyethylene, whoserepeating unit is based onethylenemonomer. However,other structures do exist; forexample, elements such as
http://en.wikipedia.org/wiki/List_of_synthetic_polymershttp://en.wikipedia.org/wiki/List_of_synthetic_polymershttp://en.wikipedia.org/wiki/Synthetic_rubberhttp://en.wikipedia.org/wiki/Bakelitehttp://en.wikipedia.org/wiki/Neoprenehttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/PVChttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Polypropylenehttp://en.wikipedia.org/wiki/Polyacrylonitrilehttp://en.wikipedia.org/wiki/Polyvinyl_butyralhttp://en.wikipedia.org/wiki/Siliconehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/List_of_synthetic_polymershttp://en.wikipedia.org/wiki/List_of_synthetic_polymershttp://en.wikipedia.org/wiki/Synthetic_rubberhttp://en.wikipedia.org/wiki/Bakelitehttp://en.wikipedia.org/wiki/Neoprenehttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/PVChttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Polypropylenehttp://en.wikipedia.org/wiki/Polyacrylonitrilehttp://en.wikipedia.org/wiki/Polyvinyl_butyralhttp://en.wikipedia.org/wiki/Siliconehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Monomer


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silicon form familiar materialssuch as silicones, examples

being silly putty andwaterproof plumbing sealant.Oxygen is also commonlypresent in polymerbackbones, such as those ofpolyethylene glycol,polysaccharides (in glycosidicbonds), and DNA (inphosphodiester bonds).

Polymerization is theprocess of combining manysmall molecules known asmonomers into a covalentlybonded chain. During thepolymerization process, somechemical groups may be lostfrom each monomer.The
http://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Silly_puttyhttp://en.wikipedia.org/wiki/Polyethylene_glycolhttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Glycosidic_bondhttp://en.wikipedia.org/wiki/Glycosidic_bondhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Phosphodiester_bondhttp://en.wikipedia.org/wiki/Small_moleculeshttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Silly_puttyhttp://en.wikipedia.org/wiki/Polyethylene_glycolhttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Glycosidic_bondhttp://en.wikipedia.org/wiki/Glycosidic_bondhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Phosphodiester_bondhttp://en.wikipedia.org/wiki/Small_molecules


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distinct piece of eachmonomer that is incorporated

into the polymer is known as arepeat unit or monomerresidue.

Biopolymers are polymersproduced by living organisms.Since they are polymers,Biopolymers contain

monomeric units that arecovalently bonded to formlarger structures. There arethree main classes ofbiopolymers based on the

differing monomeric unitsused and the structure of thebiopolymer formed.
http://en.wikipedia.org/wiki/Repeat_unithttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Monomerichttp://en.wikipedia.org/wiki/Repeat_unithttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Monomeric


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Polynucleotides long polymerswhich are composed of 13 or

more nucleotidemonomers,Polypeptides short polymersof amino acids, andPolysaccharides which areoften linear bonded polymericcarbohydrate structures. [1][2][3][4]

Cellulose is the most commonorganic compound and

biopolymer on Earth. About 33percent of all plant matter iscellulose. The cellulosecontent of cotton is 90percent and that of wood is 50percent.Biopolymers often have a welldefined structure, though this
http://en.wikipedia.org/wiki/Polynucleotidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Monomershttp://en.wikipedia.org/wiki/Polypeptideshttp://en.wikipedia.org/wiki/Polysaccharideshttp://en.wikipedia.org/wiki/Biopolymer#cite_note-0http://en.wikipedia.org/wiki/Biopolymer#cite_note-1http://en.wikipedia.org/wiki/Biopolymer#cite_note-2http://en.wikipedia.org/wiki/Biopolymer#cite_note-3http://en.wikipedia.org/wiki/Cellulosehttp://en.wikipedia.org/wiki/Polynucleotidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Monomershttp://en.wikipedia.org/wiki/Polypeptideshttp://en.wikipedia.org/wiki/Polysaccharideshttp://en.wikipedia.org/wiki/Biopolymer#cite_note-0http://en.wikipedia.org/wiki/Biopolymer#cite_note-1http://en.wikipedia.org/wiki/Biopolymer#cite_note-2http://en.wikipedia.org/wiki/Biopolymer#cite_note-3http://en.wikipedia.org/wiki/Cellulose


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biopolymer composed of 13 ormore[1]nucleotidemonomers

covalently bonded in a chain.DNA (deoxyribonucleic acid)and RNA (ribonucleic acid) areexamples of polynucleotideswith distinct biologicalfunction. The prefix polycomes from the ancient Greek (polys, many). DNAconsists of two chains of

polynucleotides, with eachchain in the form of a helicalspiral.The genome of anorganism consists ofcomplementary pairs of

enormously longpolynucleotides wound aroundeach other in the form of a
http://en.wikipedia.org/wiki/Biopolymerhttp://en.wikipedia.org/wiki/Polynucleotide#cite_note-0http://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Ancient_Greekhttp://en.wikipedia.org/wiki/Genomehttp://en.wikipedia.org/wiki/Biopolymerhttp://en.wikipedia.org/wiki/Polynucleotide#cite_note-0http://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Ancient_Greekhttp://en.wikipedia.org/wiki/Genome


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double helix.

Nucleotides are moleculesthat, when joined together,make up the structural unitsofRNA and DNA.They form the rungs of theDNA ladder and are therepeating units in DNA. Thereare four types of nucleotides

(A, T, G and C) and it is thesequence of these nucleotidesthat carries information.Anucleotide is composed of anucleobase (nitrogenous

base), a five-carbon sugar(either ribose or 2'-deoxyribose), and one to
http://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Nucleobasehttp://en.wikipedia.org/wiki/Ribosehttp://en.wikipedia.org/wiki/Deoxyribosehttp://en.wikipedia.org/wiki/Deoxyribosehttp://en.wikipedia.org/wiki/Double_helixhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Nucleobasehttp://en.wikipedia.org/wiki/Ribosehttp://en.wikipedia.org/wiki/Deoxyribosehttp://en.wikipedia.org/wiki/Deoxyribose


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three phosphate groups.Together, the nucleobase and

sugar comprise a nucleoside.The phosphate groups formbonds with either the 2, 3, or5-carbon of the sugar, withthe 5-carbon site mostcommon. Cyclic nucleotidesform when the phosphategroup is bound to two of thesugar's hydroxyl groups.[1]

Ribonucleotides arenucleotides where the sugar isribose, anddeoxyribonucleotides containthe sugar deoxyribose.

Nucleotides can contain eithera purine or a pyrimidine base.Nucleic acids are polymeric
http://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Nucleosidehttp://en.wikipedia.org/wiki/Chemical_bondshttp://en.wikipedia.org/wiki/Cyclic_nucleotidehttp://en.wikipedia.org/wiki/Hydroxyl#Hydroxyl_grouphttp://en.wikipedia.org/wiki/Nucleotide#cite_note-Alberts-0http://en.wikipedia.org/wiki/Ribonucleotideshttp://en.wikipedia.org/wiki/Ribosehttp://en.wikipedia.org/wiki/Deoxyribonucleotideshttp://en.wikipedia.org/wiki/Deoxyribosehttp://en.wikipedia.org/wiki/Purinehttp://en.wikipedia.org/wiki/Pyrimidinehttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Nucleosidehttp://en.wikipedia.org/wiki/Chemical_bondshttp://en.wikipedia.org/wiki/Cyclic_nucleotidehttp://en.wikipedia.org/wiki/Hydroxyl#Hydroxyl_grouphttp://en.wikipedia.org/wiki/Nucleotide#cite_note-Alberts-0http://en.wikipedia.org/wiki/Ribonucleotideshttp://en.wikipedia.org/wiki/Ribosehttp://en.wikipedia.org/wiki/Deoxyribonucleotideshttp://en.wikipedia.org/wiki/Deoxyribosehttp://en.wikipedia.org/wiki/Purinehttp://en.wikipedia.org/wiki/Pyrimidinehttp://en.wikipedia.org/wiki/Nucleic_acid


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macromolecules made fromnucleotide monomers. In DNA,

the purine bases are adenineand guanine, while thepyrimidines are thymine andcytosine. RNA uses uracil inplace of thymine. Adeninealways pairs with thymine by2 hydrogen bonds, whileguanine pairs with cytosinethrough 3 hydrogen bonds,

each due to their uniquestructures.Sets of three nucleotides,known as codons, eachcorrespond to a specific amino

acid or to a signal;
http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Cytosinehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Codonhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Cytosinehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Uracilhttp://en.wikipedia.org/wiki/Codon


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molecule (pronounced /mlkjul/ ) is an electrically

neutral group of at least twoatoms held together bycovalentchemical bonds.[1] [2][3] [4] [5] [6] Molecules aredistinguished from ions bytheir electrical charge.However, in quantum physics,organic chemistry, andbiochemistry, the term

molecule is often used lessstrictly and applied topolyatomic ions.

In the kinetic theory ofgases,the term molecule is oftenused for any gaseous particleregardless of its composition.According to this definition
http://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Chemical_bondhttp://en.wikipedia.org/wiki/Molecule#cite_note-iupac-0http://en.wikipedia.org/wiki/Molecule#cite_note-iupac-0http://en.wikipedia.org/wiki/Molecule#cite_note-1http://en.wikipedia.org/wiki/Molecule#cite_note-1http://en.wikipedia.org/wiki/Molecule#cite_note-2http://en.wikipedia.org/wiki/Molecule#cite_note-2http://en.wikipedia.org/wiki/Molecule#cite_note-3http://en.wikipedia.org/wiki/Molecule#cite_note-3http://en.wikipedia.org/wiki/Molecule#cite_note-4http://en.wikipedia.org/wiki/Molecule#cite_note-4http://en.wikipedia.org/wiki/Molecule#cite_note-5http://en.wikipedia.org/wiki/Molecule#cite_note-5http://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Quantum_physicshttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/Kinetic_theoryhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Wikipedia:IPA_for_Englishhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Chemical_bondhttp://en.wikipedia.org/wiki/Molecule#cite_note-iupac-0http://en.wikipedia.org/wiki/Molecule#cite_note-1http://en.wikipedia.org/wiki/Molecule#cite_note-2http://en.wikipedia.org/wiki/Molecule#cite_note-3http://en.wikipedia.org/wiki/Molecule#cite_note-4http://en.wikipedia.org/wiki/Molecule#cite_note-5http://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Quantum_physicshttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Biochemistryhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/Kinetic_theoryhttp://en.wikipedia.org/wiki/Gas


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noble gas atoms areconsidered molecules despite

the fact that they arecomposed of a single non-bonded atom.[7]

A molecule may consist of

atoms of a single chemicalelement, as with oxygen (O2),or of different elements, aswith water (H2O). Atoms andcomplexes connected by non-

covalent bonds such ashydrogen bonds or ionicbonds are generally notconsidered single molecules.[8]

Molecules as components ofmatter are common in organicsubstances (and therefore
http://en.wikipedia.org/wiki/Noble_gashttp://en.wikipedia.org/wiki/Molecule#cite_note-6http://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Water_(molecule)http://en.wikipedia.org/wiki/Hydrogen_bondhttp://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Molecule#cite_note-7http://en.wikipedia.org/wiki/Noble_gashttp://en.wikipedia.org/wiki/Molecule#cite_note-6http://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Water_(molecule)http://en.wikipedia.org/wiki/Hydrogen_bondhttp://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Molecule#cite_note-7


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as in diamond or sodiumchloride). The theme of

repeated unit-cellular-structure also holds for mostcondensed phases withmetallic bonding. In glasses(solids that exist in a vitreousdisordered state), atoms mayalso be held together bychemical bonds without anydefinable molecule, but also

without any of the regularityof repeating units thatcharacterises crystals.

covalent bond is a form ofchemical bonding that ischaracterized by the sharingof pairs ofelectrons between
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degree ofcovalent bonding.Thus, an ionic bond is

considered a bond where theionic character is greater thanthe covalent character. Thelarger the difference inelectronegativity between thetwo atoms involved in thebond, the more ionic (polar)the bond is. Bonds withpartially ionic and partially

covalent character are calledpolar covalent bonds.

Ionic compounds conductelectricity when molten or insolution, but not as a solid.They generally have a highmelting point and tend to besoluble in water.
http://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Electronegativityhttp://en.wikipedia.org/wiki/Polar_covalent_bondhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Melting_pointhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Electronegativityhttp://en.wikipedia.org/wiki/Polar_covalent_bondhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Melting_point


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ion is an atom or molecule inwhich the total number ofelectrons is not equal to thetotal number ofprotons,giving it a net positive or

negative electrical charge.The name was given byphysicist Michael Faraday forthe substances that allow acurrent to pass ("go")

between electrodes in asolution, when an electric fieldis applied. It is from Greek ,meaning "going."

An anion (pronounced /n.a.n/ AN -eye-n ), fromthe Greek word (n),meaning "up", is an ion with
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An ion consisting of a singleatom is an atomic or

monatomic ion; if it consistsof two or more atoms, it is amolecular or polyatomicion.

chromosome is an organizedstructure ofDNA and proteinthat is found in cells. It is asingle piece of coiled DNAcontaining many genes,regulatory elements and othernucleotide sequences.Chromosomes also contain

DNA-bound proteins, whichserve to package the DNA andcontrol itsfunctions.Chromosomes vary
http://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Monatomic_ionhttp://en.wikipedia.org/wiki/Molecularhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Regulatory_sequencehttp://en.wikipedia.org/wiki/Genetic_sequencehttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Monatomic_ionhttp://en.wikipedia.org/wiki/Molecularhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/Polyatomic_ionhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Regulatory_sequencehttp://en.wikipedia.org/wiki/Genetic_sequence


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widely between differentorganisms. The DNA molecule

may be circular or linear, andcan be composed of 10,000 to1,000,000,000[1]nucleotidesin a long chain. Typically,eukaryotic cells (cells withnuclei) have large linearchromosomes and prokaryoticcells (cells without definednuclei) have smaller circular

chromosomes, although thereare many exceptions to thisrule. Also, cells may containmore than one type ofchromosome; for example,

mitochondria in mosteukaryotes and chloroplasts inplants have their own small
http://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Chromosome#cite_note-0http://en.wikipedia.org/wiki/Nucleotideshttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Prokaryotichttp://en.wikipedia.org/wiki/Mitochondriahttp://en.wikipedia.org/wiki/Eukaryoteshttp://en.wikipedia.org/wiki/Chloroplastshttp://en.wikipedia.org/wiki/Organismhttp://en.wikipedia.org/wiki/Chromosome#cite_note-0http://en.wikipedia.org/wiki/Nucleotideshttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Prokaryotichttp://en.wikipedia.org/wiki/Mitochondriahttp://en.wikipedia.org/wiki/Eukaryoteshttp://en.wikipedia.org/wiki/Chloroplasts


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chromosomes.In eukaryotes, nuclear

chromosomes are packagedby proteins into a condensedstructure called chromatin.This allows the very long DNAmolecules to fit into the cellnucleus. The structure ofchromosomes and chromatinvaries through the cell cycle.Chromosomes are the

essential unit for cellulardivision and must bereplicated, divided, andpassed successfully to theirdaughter cells so as to ensure

the genetic diversity andsurvival of their progeny.Chromosomes may exist as
http://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Offspringhttp://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Offspring


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either duplicated orunduplicated. Unduplicated

chromosomes are single linearstrands, whereas duplicatedchromosomes (copied duringsynthesis phase) contain twocopies joined by a centromere

Chromosomes are long,stringy aggregates of genesthat carry heredityinformation. They are

composed ofDNA andproteins and are locatedwithin the nucleus of our cells.Chromosomes determineeverything from hair color andeye color to sex. Whether youare a male or female dependson the presence or absence of
http://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/Centromerehttp://biology.about.com/od/geneticsglossary/g/chromosome.htmhttp://biology.about.com/library/weekly/aa051701a.htmhttp://biology.about.com/library/weekly/aa050301a.htmhttp://biology.about.com/od/cellanatomy/p/nucleus.htmhttp://biology.about.com/od/cellbiology/a/cells-facts.htmhttp://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/Centromerehttp://biology.about.com/od/geneticsglossary/g/chromosome.htmhttp://biology.about.com/library/weekly/aa051701a.htmhttp://biology.about.com/library/weekly/aa050301a.htmhttp://biology.about.com/od/cellanatomy/p/nucleus.htmhttp://biology.about.com/od/cellbiology/a/cells-facts.htm


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certain chromosomes.

Human cells contain 23 pairsof chromosomes for a total of46. There are 22 pairs ofautosomes and one pair ofsex chromosomes. The sexchromosomes are the Xchromosome and the Ychromosome.chromosome consists of a

single, very long DNA helix onwhich thousands of genes areencoded

Transcription

The process of genetictranscription produces asingle-stranded RNA molecule
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known as messenger RNA,whose nucleotide sequence is

complementary to the DNAfrom which it was transcribed.

Translation

Translation is the process by

which a mature mRNAmolecule is used as atemplate for synthesizing anew protein. Translation is

carried out by ribosomes,large complexes of RNA andprotein responsible forcarrying out the chemicalreactions to add new amino

acids to a growing polypeptidechain by the formation ofpeptide bonds. The geneticcode is read three nucleotides
http://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Translation_(genetics)http://en.wikipedia.org/wiki/Mature_messenger_RNAhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Polypeptide_chainhttp://en.wikipedia.org/wiki/Polypeptide_chainhttp://en.wikipedia.org/wiki/Peptide_bondhttp://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Translation_(genetics)http://en.wikipedia.org/wiki/Mature_messenger_RNAhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Polypeptide_chainhttp://en.wikipedia.org/wiki/Polypeptide_chainhttp://en.wikipedia.org/wiki/Peptide_bond


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at a time, in units calledcodons, via interactions with

specialized RNA moleculescalled transfer RNA (tRNA).

DNA replication andinheritance

The growth, development,and reproduction of organismsrelies on cell division, or theprocess by which a single cell

divides into two usuallyidentical daughter cells. Thisrequires first making aduplicate copy of every genein the genome in a process

called DNA replication. Thecopies are made byspecialized enzymes known as
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DNA polymerases, which"read" one strand of the

double-helical DNA, known asthe template strand, andsynthesize a newcomplementary strand.Because the DNA double helixis held together by basepairing, the sequence of onestrand completely specifiesthe sequence of its

complement; hence only onestrand needs to be read bythe enzyme to produce afaithful copy. The process ofDNA replication is

semiconservative; that is, thecopy of the genome inheritedby each daughter cell
http://en.wikipedia.org/wiki/DNA_polymerasehttp://en.wikipedia.org/wiki/Base_pairhttp://en.wikipedia.org/wiki/Base_pairhttp://en.wikipedia.org/wiki/Semiconservative_replicationhttp://en.wikipedia.org/wiki/DNA_polymerasehttp://en.wikipedia.org/wiki/Base_pairhttp://en.wikipedia.org/wiki/Base_pairhttp://en.wikipedia.org/wiki/Semiconservative_replication


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contains one original and onenewly synthesized strand of

DNA.[8]After DNA replication iscomplete, the cell mustphysically separate the two

copies of the genome anddivide into two distinctmembrane-bound cells.

Interactions with

proteinsAll the functions of DNAdepend on interactions withproteins. These protein

interactions can be non-specific, or the protein canbind specifically to a singleDNA sequence. Enzymes can
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also bind to DNA and of these,the polymerases that copy the

DNA base sequence intranscription and DNAreplication are particularlyimportant.

Structural proteins that bindDNA are well-understoodexamples of non-specific DNA-protein interactions. Withinchromosomes, DNA is held in

complexes with structuralproteins. These proteinsorganize the DNA into acompact structure calledchromatin.

Chromatin
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Mass of genetic materialcomposed ofDNA and

proteins that condense toform chromosomes duringeukaryotic cell division.Chromatin is located in thenucleus of a cell.
http://biology.about.com/od/geneticsglossary/g/DNA.htmhttp://biology.about.com/od/basicgenetics/p/chromosgender.htmhttp://biology.about.com/od/cellanatomy/p/nucleus.htmhttp://biology.about.com/od/cellanatomy/a/eukaryprokarycells.htmhttp://biology.about.com/od/geneticsglossary/g/DNA.htmhttp://biology.about.com/od/basicgenetics/p/chromosgender.htmhttp://biology.about.com/od/cellanatomy/p/nucleus.htmhttp://biology.about.com/od/cellanatomy/a/eukaryprokarycells.htm

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