中国农业大学分子生物学课件

A nucleic acid consists of a polynucleotide chain. nitrogenous base is linked to the sugar. DNA takes its name from its sugar (2deoxyribose); RNA is named for its sugar (ribose). The difference is that the sugar in RNA has an OH group at the 2 position of the pentose ring.
DNA is a main genetic material
RNA is genetic material also R酸之外的
其他遗传物质？
Is the protein genetic material ?
复制 ? 表面遗传信息 ?
Prion (proteinaccous infections particle)
Phosphodiester bonds (磷酸二脂键) :
Covalent linkage of a phosphate group between the 5’hydroxyl of a ribose and the 3’-hydroxyl of the next.
At neutral pH, each phosphate group has a single negative charge, this is why nucleic acids are termed acids; they are the anions of strong acids. Nucleic acids are thus highly charged polymers.
§ 2-5 Denaturation and Renaturation § 2-6 Supercoiled DNA and Topoisomerase § 2-7 Restriction Enzymes and DNA Sequencing
§ 2-1 DNA is the genetic material
1. Nitrogenous base Nucleotide (Nt) basic unit
Each nucleic acid contains 4 types of base. The same two purines, adenine and guanine, are present in both DNA and RNA. The two pyrimidines in DNA are cytosine and thymine; in RNA uracil is found instead of thymine.
1952
Martha Chase & Alfred Hershey Used phages in which the protein was labeled with 35S and the DNA with 32P for the final proof that DNA is the molecule of heredity.
不含大于100nt的核酸
Conclusion:
•Genes are made of nucleic acid, usually DNA •Some simple genetic systems such as viruses have RNA genes
• DNA作为遗传物质的优点 (自然选择的优势)
The only difference between uracil and thymine is the presence of a methyl substituent at position C5.
The bases are usually referred to by their initial letters. DNA contains A, G, C, T, while RNA contains A, G, C, U
2. Transformation in Bacteria
• Key experiments done by Frederick Griffith in 1928 • Observed change in Streptococcus pneumoniae — from virulent (S) smooth colonies where bacterial had capsules, to avirulent (R) rough colonies without capsules • Heat-killed virulent colonies could transform avirulent colonies to virulent ones
传染性病原蛋白颗粒引起的风波
羊痒疫 (scripie) 人类 kuru 病 boving spongiform encephalopathy(疯牛病) 28kD 的疏水性糖蛋白
由核基因组基因
PrP（Prion related Protein）编码
可被蛋白酶K抑制
高度纯化的病体脑 组织的感染性粒子
不被核酸酶和辐射灭活
The terminal nucleotide at one end of the chain has a free 5′ group; the terminal nucleotide at the other end has a free 3′ group. It is conventional to write nucleic acid sequences in the 5′→3′ directionthat is, from the 5′ terminus at the left to the 3′ terminus at the right.
deoxyribonucleic acid (DNA) DNA is the storehouse, or cell library, that contains all the information required to build the cells and tissues of an organism.
base + sugar = nucleoside
RNA: ribonucleosides or just nucleosides;
DNA: 2’-deoxyribonucleosides or just deoxynucleosides
Nucleotides ( 核苷酸 ) :
base + sugar + phosphate = nucleotides The nucleoside 5’-triphosphates (NTPs or dNTPs) are respectively the building blocks of polymeric RNA and DNA
The nitrogenous base is linked to position 1 on the pentose ring by a glycosidic bond from N1 of pyrimidines or N9 of purines. Nucleoside Nucleotide
Nucleosides ( 核苷 ) :
A nucleic acid consists of a chemically linked sequence of subunits. Each subunit contains a nitrogenous base, a pentose sugar, and a phosphate group.
DNA: The Transforming Material
In 1944 Avery used a transformation test similar to Griffith’s procedure taking care to define the chemical nature of the transforming substance – Techniques used excluded both protein and RNA as the chemical agent of transformation – Other treatments verified that DNA is the chemical agent of transformation of S. pneumoniae from avirulent to virulent Griffith, 1928; Avery et al., 1944
★ 储存遗传信息量大 1kb DNA序列 41000 种遗传信息
★A-T, C-G 互补
双螺旋结构
复制, 转录
遗传稳定
★ 核糖的2’ – OH 脱氧 ★ 可以突变 方便修复
在水溶液中的稳定性高于RNA
以求不断进化 以求稳定遗传
§ 2-2 The Chemical Nature of Polynucleotides •Levene, Jacobs, et al. characterized basic composition of DNA and RNA
The polynucleotide chain is constructed by linking the 5′ position of one pentose ring to the 3′ position of the next pentose ring via a phosphate group. So the sugar-phosphate backbone is said to consist of 5′-3′ phosphodiester linkages. The nitrogenous bases "stick out" from the backbone.