分子生物学 DNA.pptVIP

2.2.1 common structure and proofreading mechanism of DNA polymerases ---Pol I Pol III * * DNA replication (复制) 1. Overview A parental duplex of DNA is replicated to form two daughter duplexes, each of which consists of one parental strand and one (newly synthesized) daughter strand.This behavior is called semiconservative (半保留) replication. 1.1 concepts The replicon (复制子) is a unit of the genome in which DNA is replicated. Each replicon contains an origin for initiation of replication. The origin (起始点) is a sequence of DNA at which replication is initiated. The terminus (终点) is a segment of DNA at which replication ends. A replication fork (Growing point) is the point at which strands of parental duplex DNA are separated so that replication can proceed. A replication eye is a region in which DNA has been replicated within a longer, unreplicated region. Semidiscontinuous replication is mode in which one new strand is synthesized continuously while the other is synthesized discontinuously. Okazaki fragments are the short stretches produced during discontinuous replication; they are later joined into a covalently intact strand. Leading strand: Continuous Lagging strand: Discontinuous Okazaki fragments Single-replicon vs Multi-replicon Unidirection vs Bidirection Linear DNA vs circular DNA Single strand vs double strands 1.2 Models of DNA replication Theta (θ) mode replication When a replicon is circular, the presence of an eye forms the θ-structure Displacement loop replication /D loop replication Rolling circle replication 1.3 Priming is required to start DNA synthesis A primer is a short sequence (often of RNA) that is paired with one strand of DNA and provides a free 3’-OH end at which a DNA polymerase starts synthesis of a deoxyribonucleotide chain. A sequence of RNA synthesized on the template (cellular DNA) A preformed RNA pairs with the template (retrovirus) A primer terminus generated within duplex DNA. (rolling circle replication) priming nuc