文档介绍：Chapter 3
Nucleic Acid Structure
Key Points
Deoxyribonucleic acid (DNA) contains all the information required for building the cells and tissues of anism
Exact replication of DNA assures its ic continuity from generation to generation and is critical to the development of an individual
The information stored in DNA is arranged in hereditary units (genes) that control identifiable traits of anism
In the process of transcription, the information stored in DNA is copied into ribonucleic acid (RNA), which has three distinct roles (tRNA, rRNA and mRNA) in protein synthesis
mRNA carries the instructions from DNA that specifies the correct order of amino acids during protein synthesis
In the process of translation, the information in mRNA is interpreted by transfer RNA (tRNA) with the aid of ribosomal RNA (rRNA) and its associated proteins
Bases
The bases (碱基)are heterocyclic aromatic rings, purines (A,G) are bicyclic (two fused rings) and pyrimidines (C, T and U ) are monocyclic structures
Nucleosides
The bases are covalently linked to the 1'-position of a pentose sugar ring to form nucleosides(核苷)
The bond between the bases and the sugars is the glycosidic bond(糖苷键)
Nucleotides
One or more phosphate groups bind covalently to the 3 '-, 5 '- (in ribonucleotides only) or 2 ' -position of the nucleoside to form nucleotides(核苷酸)
Deoxyribonucleotides or ribonucleotides are joined into a polymer by the covalent linkage of a phosphate group, phosphodiester bond (磷酸二酯键) between the 5 ' -hydroxyl of one ribose and the 3 ' -hydroxyl of the next
DNA Double Helix
Watson and Crick’s double helix mode(1953)
Two chains of DNA are wound around each other, resulting in aright-handed double helix
The negatively charged sugar-phosphate backbones of the molecule are on the outside, and the planar (扁平的)bases in the center of the helix
Between the backbone strands run the major and minor grooves
The strands are joined noncovalently by hydrogen bonding between the bases on opposite