02 nucleic acid structure and feature

•
1. Two chains,antiparallel, right-handed, major groove and minor groove 2. outside(sugarphosphate backbone), inside(bases), 3’,5’phosphodiester bond 3. 2nm in diameter, 10bp per turn, 3.4nm 4. Base pairing
2.1 primary structure of nucleic acid
• definition：the nucletide residue sequence of
the polynucleotide chain；
• linkage：3’,5’-phosphodiester bond；
• backbone：phosphate + pentose； • direction：from the 5’ terminus to the 3’
2.3.1 nucleoside：
• DNA: 2’-deoxyribose + A、T、C、G
• RNA: ribose + A、U、C、G
• The base is linked to position 1 on a pentose
by a glycosidic bond from N1 of pyrimidine
Chapter 02:
nucleic acids structure and properties
1 Overview
1.1 type and distribution of nucleic acid
1.1.1 DNA deoxyribonucleic acid; function: The genetic information carrier, responsible for the genetic information storage and transmission； distribution： Eukaryotes: nucleus（98%）,organelle（2%）； prokaryotes: nucleoid、plasmids viruses
• The diameter of the
double helix is 2nm
• There is a complete
turn every 3.4nm,
with 10bp per turn.
•
Two chains in the double helix associate by hydrogen bonding between the bases,G with C and A with T(base pairing , complementary). Three hydrogen bond can form specifically between G and C,but only two can form between A and T;
DNA
• physical chemistry studies and acid and alkali
titrate studies on DNA base ；
2.2.1 key notes of DNA double helix
• Two polynucleotide chains in
a DNA double helix
(as templates).
1.1.2.2 tRNA
• 分子量最小；
• Functions: as adapter molecules (transport
amino acids), that faithfully translate the information in mRNA into a specific sequence of amino acids；
big(in length and molecular weight)；
• Functions: as intermediaries, carrying genetic
information from genes to ribosomes, where the corresponding proteins can be synthesized
5’
3’
小沟
大沟 3’ 5’
2.2.2 important meanings
• Explains for the first time how genetic
information is encoded in DNA and passed from one generation to the next；
terminus ；
• representation
A 'P 5 P
C P
T P
C
G A P P OH
3'
5'pApCpTpCpGpA -OH 3'
5'ACTCGA 3'
2.2 secondary structure of DNA
•
means DNA double helix
• Three discoveries (physical chemistry studies
• X~ray photograph of DNA with high quality：
DNA specimens from different species have
the same results（constant width;3.4nm）；
• Chargaff rules：the rule of the composition of
Chargaff rules：
• the base composition of DNA varies from one species to another, while DNA specimens isolated from different tissues of the same species have the same base composition； • in nature DNA,the number of G units equals the number of C units and the number of A units equals the number of T units ( this strongly hinted towards the base pair makeup of DNA )； • The base composition of DNA in a given species does not change with an organism’s age,nutritional state,or changing environment。
ribose （in RNA）
2’- deoxyribose （in DNA）
1.2.2 base
Pyrimidine ring
DNA
4
3N 2 N 1 6 1N 5 2 4 N 3
5 6
7 N N 8 9
RNA
purine ring
Modified bases
• The chemical modification of bases is
or N9 of purine
O
NH
base
N N
N
N O H
HN N
H2O
OH O
Phosphate bond
O O P OH O
OHCH2
phosphoric acid
H2O
OH OH
glycosidic bond
pentose
1.2.3.2 nucleotide
2 Nucleic acid structure
1.1.2 RNA
• ribonucleic acid； • Function: mainly participate the expression of
genetic information
• Type: rRNA（ribosomal RNA）
mRNA（messenger RNA）
tRNA（transfer RNA）
widespread, and has a number of specific
roles.
• Such as: the methylation of the N-6
position of A、the 4-amino group and the
5-position of C
1.2.3 nucleoside and nucleotide
• distribution: cytoplasm(90%), nucleus(10%)；
viruses
tRNA
rRNA
mRNA
1.1.2.1 mRNA
• 种类最多，比例最低，寿命最短；
• Each polypeptide has corresponding mRNA，
the difference among different mRNA is quite
• forms a major groove and a
minor groove
• The bases lie on the
inside ， the sugarphosphate backbone is on the outside
• The bases are flat
structure, lying in pairs perpendicular to the axis
• 每个Aa至少有一个对应的tRNA（如丙氨酸
tRNA、tRNAAla）。