分子生物学（杨君）lecture4 mutations and repair.pptVIP

Different changes of DNA Mutation is not good and is naturally repaired, thus it could not be responsible for biodiversity. Recombination is good and naturally promoted; it is responsible for diversity inside of species. Transposition is different from mutation and recombination because producing mechanism is different; no mechanism to correct it; existing in nature in a well-controlled manner (10-5). not repaired but controlled. Chapter 10 Mutability and Repair of DNA 突变和修复 DNA damage and repair summary Replication errors, repair, and defects in repair cause disease Common types of DNA damage DNA repair pathways Direct enzymatic repair Base excision repair Nucleotide excision repair Mismatch repair Double-strand break repair Non-homologous end joining Homologous recombination DNA repair defects cause disease Types of Mutations Mutant refers to an organism or a gene that is different from the normal or wild type. Mutation refers to any heritable change in the base sequence of a DNA molecule. The most common type of change is a substitution, addition, or deletion of one or more bases. A mutagen is a physical or chemical agent that causes mutations to occur (or increases the frequency of their occurrence). Types of Mutations Mutagenesis is the process of producing a mutation. spontaneous mutation: the mutation occurs in nature without the addition of a mutagen, and the resulting mutants are spontaneous mutants. induced mutagenesis the process of mutation which is caused by a mutagen. site-specific mutagenesis, a form of induced mutagenesis in which genetic engineering techniques are used to construct mutant DNA molecules containing mutations at specific, preselected locations. spontaneous mutation Mismatch Base analogues(类似物) Deamination（脱氨基） Rate of spontaneous mutation at any given site on chromosomal ranges from 10-6 to 10-11 per round of DNA replication, with some sites being “hotspot（热点）” . 4% of cytosines in a typical DNA molecule ar