第二章染色体与DNA2DNA复制,修复,转座1.pptVIP

滚环式复制 首先在动物线粒体中被发现。 一条短RNA与一条DNA互补，取 代了该区域原来的互补的DNA 链，使得两条链的合成高度不对 称，一条链上迅速合成出互补 链，另一条链则为游离的单环。 D loops 单向复制的特殊方式 DNA修复 (DNA Repair) Mutagenesis (诱变) Replication Fidelity (复制的精确性) Mutagens (诱变剂) Mutation Mutation （突变） Mutation: Permanent, heritable alterations in the base sequence of DNA. The substitution mutation(替换突变) Transition(转换): Purine or pyrimidine is replaced by the other. Transversion(颠换): a purine is replaced by a pyrimidine or vice verse. 无义突变 错义突变 沉默突变 Thumb DNA polymerase Thumb domain: 1. Not directly involved in catalysis 2. Interacts with the synthesized DNA to maintain correct position of the primer and the active site, and to maintain a strong association between DNA Pol and its substrate. DNA polymerase are processive enzymes ? Processivity (持续合成能力) Processivity is a characteristic of enzymes that operate on polymeric substrates. ? For DNA polymerase, the degree of processivity is defined as the average number of nucleotides added each time the enzyme binds a primer:template junction (a few~50,000). DNA polymerases synthesis DNA in a processive manner Structure of a sliding DNA clamp Sliding DNA clamps encircle the newly replicated DNA produced by an associated DNA polymerase. Sliding clamps dramatically increase DNA polymerase processivity (持续合成能力) The composition of the DNA Pol III holoenzyme Three enzymes: ? Two copies of the DNA Pol III core enzyme ? One copy of the γ-complex The “trombone” model for coordinating replication by two DNA polymerase at the E. coli replication fork Steps in the synthesi of the lagging strand Removal of RNA primers from newly synthesized DNA RNAse H removes all of the RNA primer except the ribonucleotide directly linked to the DNA end. An exonuclease removes the final ribonucleotide. DNA polymerase fills the gap, leaving a a break in the backbone between the 3’OH and 5’ phosphate of the repaired strand. DNA ligase repaires this “nick”. 当复制叉前移，遇到20bp重复性终止子序列 (Ter)时，Ter-