Chapter 2 Nucleic Acid Chemistry

Chapter 2 Nucleic Acid ChemistryChapter 2 Nucleic Acid Chemistry

ComposationComposation

StructureStructure

FunctionFunction

DNADNA

RNARNA

1868 Fridrich Miescher first isolated nuclein from pyocyte.

1944 O.Avery confirmed DNA is hereditary substance.

1953 J.Watson F.Crick discovered DNA double helix.

1968 Nirenberg found the genetic code .

introduction

Francis Harry Compton Crick

James Dewey Watson

Marshall W. Nirenberg

Nucleic acid is a polymer of nucleotide ,having and transfering genetic information, include deoxyribonucleic acid (DNA)and ribonucleic acid(RNA).

DNA RNA

laying Nucleus90%,mitochondrium, autoplast, plasmid.

Nucleus, cytochyma

function Having genetic information and deciding genotye o

f body.

Jion in genetic expression.

Section 1 composition of nucleic acid

DNA RNAbase Purine base

s 嘌呤碱Adenine 腺嘌呤

(A)Adenine 腺嘌呤

(A)

Guanine 鸟嘌呤 (G)

Guanine 鸟嘌呤 (G)

Pyrimidine bases 嘧啶碱

Cytosine 胞嘧啶 (C)

Cytosine 胞嘧啶 (C)

Thymine 胸腺嘧啶(T)

Uracil 尿嘧啶 (U)

pentose D-2-deoxyribose D-2- 脱氧核糖

D-ribose

D- 核糖acid phosphoric

acidphosphoric acid

Ribonucleoside 核苷 The linkage of base with ribose(2-deoxyribose) by glycoside formed ribonucleoside 　 (deoxynucleoside 脱氧核苷 ).

核苷：腺苷 AR, 鸟苷 GR, 胞苷CR, 尿苷 UR 。

脱氧核苷：脱氧腺苷 dAR, 脱氧鸟苷 dGR, 脱氧胞苷 dCR, 脱氧胸苷 dTR 。

cytidine 胞苷 CR

guanine deoxyriboside脱氧鸟苷 dGR

脱氧鸟苷酸 dGMP

胞苷酸 CMP

Nucleotide 核苷酸The product of ribonucleoside linking of phosphoric acid at 5’ position.

核苷酸：腺苷酸 AMP, 鸟苷酸 GMP, 胞苷酸 CMP, 尿苷酸 UMP 。

脱氧核苷酸：脱氧腺苷酸 dAMP, 脱氧鸟苷酸dGMP, 脱氧胞苷酸 dCMP, 脱氧胸苷酸 dTMP 。

Important nucleotide

DNA

DNA was formed by linking of deoxynucleotides with phosphodiester bond at 3’ position of one deoxynucleotide and 5’ position of another deoxynucleotide.

So is the RNA formation mode, difference is the nucleotide.

Section 2 Dimensional structure and function of DNA

1.Double-stranded helixThe two strands are antiparallel.

The chain, phosphoric acid and deoxyribose, locate lateral of the helix, but bases are in the helix.

Pair strictly A to T, G to C.

A turn contains 10 nucleotides, with height 3.4nm.

Width 2.0nm.

Form a major groove and a minor groove.

Rotating right-handed.

The maintaining force of the structure is hydrogen-bond.

Pairs bases

Watson and Crick2.0 nm

小沟

大沟

The Nobel Prize in Physiology or Medicine 1962 (1953)

A 型结构 碱基平面倾斜 20º ，螺旋变粗变短，螺距2 ～ 3nm 。Z 型结构 左手螺旋，只有小沟

Versatility of DNA double helix

2.Tertiary structure of DNA----supercoil

负超螺旋正超螺旋

Further coil of the DNA double helix.

3. Nucleosome

核小体

DNA: ~200bp

Histone:

H1,

H2A,H2B

H3,H4.

4.Function of DNA

Containing genetic information, as the template of gene duplication , DNA finally directs protein biosynthesis. As a result, keeping hereditary characters of body.

Gene refer to a segment of DNA chain which posseses a special biological function.

Section3 spatial structure and function of RNA

Nuclus and cytochyma

mitochondrium

function

核蛋白体RNA

rRNA mt rRNA Component of ribosome

信使 RNA

mRNA mt mRNA Template of protein synthesis

转运 RNA

tRNA mt tRNA Transport amino acids

不均一核RNA

HnRNA Precursor of mature mRNA

小核 RNA

SnRNA Jion in hnRNA splicing and transporting

小核仁 RNA

SnoRNA Processing and modifying of rRNA

RNAs in animal cell

mRNA--messenger RNA

5’cap:m7GpppNm-

3’Poly A tail ： An n=20—200

Single chain

half life time from munits to hours

tRNA

--transfer RNA

Stem-loop structure, cloverleaf pattern 三叶草形 .

3 loop and 1 arm: DHU loop, anticoden loop, Tφloop, AA arm.

Anticoden and CCA-OH 3’end.

Contain rare bases 10%-20%.

HN NH

O

O

R

HN

N N

N

O

R

HN

N

R

H

HH

H

O

O

N

N N

N

OH

H2N

CH3

R

Rare bases

Ψ I DHU mG

Ψ ： pseudouracil 假尿嘧啶， I ： hypoxanthine 次黄嘌呤，DHU ： dihydrouracil 二氢尿嘧啶， mG ： 7-methylguanine7- 甲基鸟嘌呤．

tRNA tertiary structure:

a inverse L like.

small subunit

large subunit

mRNAlocation

EF-G

tRNA

tRNA functions as a amino acid transfer in protein biosynthesis.

rRNA

--ribosomal RNA

Eukaryote 18S rRNA

Weight 80% of total RNA in a cell.

Flower like.

Component of ribosome.

procaryote ： 5S,16S,23S; eukaryote: 18S,5S,5.8S,28S

Section 4. physical and chemical properties of nucleic acid

1.General character

acidity.

high viscosity of DNA

breaking easily

2. Ultraviolet absorptionNucleic acids get their maximum absorption at 260nm.

DNA solution ： A260

／ A280=1.8; RNA solution ： A260 ／ A280

= 2.0

OD260=1.0, equal to 50μg/ml DS DNA, 40μg/ml SS DNA or RNA.

3. DNA denaturation

--the double chain change into single chain.

Methods: heat, acid, base, urea, acetone

Result: OD260↑, viscosity↓, activity lose.

Tm

--melting temperature, 解开链温度，融解温度， refer to 　 the middle point of temperature range of DNA thermal denaturation .

The temperature of 50% double chain undoing.

Tm=69.3+0.41(G+C)%

4.Renaturation and hybridization

Renaturation: the single DNA chains recover their natural double helix structure.

Annealing 退火 : renaturation of thermal denatural DNA, by way of slow cooling.

Hybridization 杂交： phenomenon of single chain DNA or RNA bind the chain different origin in renaturation process.

Section 5. nucleases 核酸酶

Nuclease: hydrolysis of nucleic acid.

DNase: hydrolysis of DNA.

RNase: hydrolysis of RNA.

exonuclease 外切酶： act at the end of the chain

endonuclease 核酸内切酶： act at the inner part of the chain

restriction enzyme 限制性内切酶： cut a special point of the chain.

ribozyme 核酶： consists of RNA, not protein.

选择题练习核酸化学

1. The element that could be used in nucleic acid quantitation is ( )

A. C

B. O

C. N

D. H

E. P

2. The basic unit composition of nucleic acid is ( )

A. Ribose and deoxyribose

B. phosphoric acid and pentaglucose

C. Pentaglucose and basic group

D. mononucleotide

E. phosphoric acid ， pentose and basic group

3 ．脱氧核糖核苷酸彻底水解，生成的产物的产物是 ( )

A 核糖和磷酸

B 脱氧核糖和碱基

C 脱氧核糖和磷酸

D 磷酸，核糖和碱基

E 脱氧核糖，磷酸和碱基

4 ．在核酸分子中核苷酸之间的连接方式是 ( )

A. 3’,3’ －磷酸二酯键

B. 糖苷键

C. 2’,5’ －磷酸二酯键

D. 肽键

E. 3’,5’ －磷酸二酯键

5. The ultraviolet absorption maximum of nucleic acid is about ( )

A. 220nm

B. 240nm

C. 260nm

D. 280nm

E. 300nm

6. 含有稀有碱基比例较多的核酸是 ( )

A. mRNA

B. DNA

C. tRNA

D. rRNA

E. hnRNA

7. 核酸分子中储存、传递遗传信息的关键部分是 ( )

A. 核苷

B. 戊糖

C. 磷酸

D. 碱基序列

E. 戊糖磷酸骨架

8 ． DNA 分子碱基含量关系哪种是错误的？

A. A+T=C+G

B. A+G=C+T

C. G=C

D. A=T

E. A/T=G/C

9. ATP 的生理功能不包括 ( )

A. 为生物反应功能

B. 合成 RNA

C. 贮存化学能

D. 合成 DNA

E. 转变为 cAMP

10. 下列哪种核酸的二级结构具有”三叶草”型 ?

A. mRNA

B. 质粒 DNA

C. tRNA

D. 线粒体 DNA

E. rRNA

11. 关于 mRNA 的论述不正确的是 ( )

A. mRNA 分子中含有生物遗传信息

B. mRNA 在生物细胞内种类最多

C. 各种 mRNA3’ 末端和 5’ 末端都有相同的结构

D. mRNA 的碱基序列可以指导多肽链的合成

E. mRNA 的所有碱基都有编码氨基酸的作用

12. The protein not in nucleosome core particle is ( )

A. H1

B. H2A

C. H2B

D. H3

E. H4

13. DNA 变性是指 ( )

A. 多核苷酸链解聚

B. DNA 分子由超螺旋变为双螺旋

C. 分子中磷酸二酯键断裂

D. 碱基间氢键断裂

E. 核酸分子的完全水解

14. DNA Tm 值较高是由于下列哪组核苷酸含量较高所致 ?

A. G+A

B. C+G

C. A+T

D. C+T

E. A+C

15. Where does DNA reside in?

A. Golgi's body

B. rough endoplasmic reticulum

C. mitochondrium

D. chromosome

E. lysosome

16. 含有腺苷酸的辅酶有 ( )

A.NAD

B.NADP

C.FAD

D.FMN

E.CoA-SH

17. 关于 tRNA 的论述不正确的是 ( )

A. 分子中含有稀有碱基

B. 分子中含有密码环

C. 是细胞中含量最多的是 RNA

D. 主要存在于胞液

E. 其二级结构为倒 L 型

18. 维持 DNA 双螺旋结构的稳定因素包括 ( )

A. 分子中的磷酸二酯键

B. 碱基对之间的氢键

C. 碱基平面间的堆积力

D. 磷酸戊糖骨架的支撑力

E. 骨架上磷酸之间的负电排斥力

19. DNA 变性的实质是 ( )

A. 多核苷酸链解聚

B. 碱基的甲基化

C. 磷酸二酯键断裂

D. 加热使碱基对间氢键断裂

E. 使 DNA 双螺旋结构松散 , 变成单链

20. What does the Tm refer to about DNA?

A. optimum temperature

B. hydrolytic temperature

C. Renaturation temperature

D. melting temperature

E. denaturation temperature

Thank you!