核酸化学 nucleic acid chemistry. contents 1 introduction 2 compositiong 3 structure 4 nucleic...
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核酸化学
Nucleic Acid Chemistry
contents
1 introduction
2 compositiong
3 Structure
4 nucleic acid and nucleotide property
ⅠIntroduction
1868, Fridrich Miescher first isolated nuclein from pyocyte( 脓细胞) .
1.discovery and development of nucleic acid
1944 O.Avery confirmed DNA is hereditary substance.
1953 J.Watson F.Crick discovered DNA double helix.
Rosalind Franklin and Maurice Wilkins showed in the early 1950s that DNA produces a characteristic x-ray diffraction pattern
A Erwin Chargaff in the late 1940s. They found that the four nucleotide bases in DNA
1968, Nirenberg found the genetic code .
Marshall W. Nirenberg
2. classification, distributing and function of nucleic acids
DNA RNA
laying Nucleus90%,mitochondrium, autoplast, plasmid.
Nucleus, cytochyma
function Having genetic information and deciding genotye of body.
Jion in genetic expression.
Ⅱ composition of nucleic acid
DNA RNA
base Purine bases
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 acid
磷酸phosphoric acid
磷酸
Nucleic Acids
Nucleotide
phosphate Ribonucleoside(deoxyribonucleoside)
base Pentose
Purine (A 、 G)
Pyrimidine (C 、 T 、 U)
deoxyriboseribose
Nucleotide
pentose
Base
9
8
16
3
7
2
1
1
8
6
7
3
1
3
Ribonucleoside
cytidine 胞苷 CR guanine deoxyriboside 脱氧鸟苷 dGR
The linkage of base with ribose(2-deoxyribose)
Deoxyribonucleotides
The product of deoxyribonucleoside linking of phosphoric acid at 5’ position.
ribonucleotides
Important nucleotides
minor bases
ΨI
Ⅲ structure of nucleic acid
1 、 structure of DNA
(1) The primary structure The primary structure of a nucleic acid is its co
valent structure and nucleotide sequence.
DNA was formed by linking of deoxynucleotides with phosphodiester bond at 3’ position of one deoxynucleotide and 5’ position of another deoxynucleotide.
The primary structure
(2) Secondary structure – Double-stranded helix
CharacteristicThe 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 Crick 2.0 nm
小沟
大沟
The Nobel Prize in Physiology or Medicine 1962 (1953)
A-DNA is favored when DNA is dehydrated. Major and minor grooves are similar in width.
B-DNA is the conformation normally found inside cells.
Z-DNA is favored in certain G/C-rich sequences. No grooves left handed helix
Versatility of DNA double helix
Versatility of DNA double helix
two sets of forces, as described earlier:
1. hydrogen bonding between complementary base pairs
2. base-stacking interactions.
forces
(3) Tertiary structure of DNA----supercoil
Further coil of the DNA double helix.
(positive supercoil) (negative supercoil)
(1) Containing genetic information, as the template of gene duplication , DNA finally directs protein biosynthesis. As a result, keeping hereditary characters of body. (2) Gene refer to a segment of DNA chain which posseses a special biological function.
(4) Function of DNA
2. 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
(1) mRNA --messenger RNA
5’cap:m7GpppNm-
3’Poly A tail : An n=20—200
Single chain
half life time from munits to hours
In prokaryotes a single mRNA molecule may code for one or several polypeptide chains. If it carries the code for only one polypeptide, the mRNA is monocistronic; if it codes for two or more different polypeptides, the mRNA is polycistronic. In eukaryotes, most mRNAs are monocistronic. mRNAs transcribed from DNA are always somewhat longer than needed simply to specify the code for the polypeptide sequence(s). The additional noncoding RNA includes sequences that regulate protein synthesis .
(2) 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%.
Secondary structure
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.
(3) rRNA
--ribosomal RNA
Weight 80% of total RNA in a cell.
Flower like.
Component of ribosome.
procaryote : 5S,16S,23S;
eukaryote: 18S,5S,5.8S,28S
Ⅳ nucleic acid and nucleotide property
Nucleic 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.
1. Ultraviolet absorption
• hyperchromic effect • The large increase in light absorption at 260 nm occurrin
g as a double-helical DNA is melted (unwound). • • hypochromic effect • The close interaction between stacked bases in a nucleic acid
has the effect of decreasing the absorption of UV light relative to a solution with the same concentration of free nucleotides. This is called the hypochromic effect.
2. 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)%
Renaturation and hybridizationRenaturation: 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.