Chapter 5 DNA mutation repair and damage-生工12.pdfVIP

Chapter 5 DNA Mutation, Damage, and Repair 第五章DNA的损伤、突变和修复 Content • Mutation • Replication errors and their repair • DNA damage • Repair of DNA damage 1 Mutation • Mutation (突变)refers to any heritable change in the base sequence of a DNA molecule. • Mutagen （突变源）is a physical or chemical agent that causes mutations to occur (or increase the frequency of their occurrence). • Mutagenesis （突变发生）is the process of producing a mutation. Life and biodiversity （生物多样性）depend on the balance between mutation and its repair • If the mutation rates （突变率）are too high, the species or the individual would be destroyed. • If there is no mutation, evolution would not go on and new species, including humans, would not have arisen. Important sources for mutation 突变的重要来源 • Inaccuracy in DNA replication: Errors； • Damage to the genetic material (spontaneously or assaulted by chemical agents and radiation) ； • Insertions generated by transposition （转 位）。 The nature of mutations 突变的类型 • 1. Point mutations Switches of one base for another The nature of mutations (continued) • 2. Insertions （插入） • 3. Deletions （缺失） • 4. Gross rearrangement of chromosome. （染色 体重排） These mutations might be caused by insertion by transposon （转座子）or by aberrant （异常）action of cellular recombination processes. • Rate of spontaneous mutation （自发突变）at any given site on chromosome ranges from 10 -6 to 10 -11 per round of DNA replication, with some sites where mutations arise at high or low frequency. • Some mutation-prone （易突变）sequences in human genome are repeats of simple di-, tri- or tetr