dna的復(fù)制ppt課件(完整版)
【正文】 nd they recruit 2 prepriming plexes of DnaBDnaC to bind, so that there is one for each of the two (bidirectional) replication forks. ? DnaB protein is delivered to oriC by DnaC protein in the form of a hexameric (DnaB:DnaC)6 plex, but DnaC protein does not enter the protein assemblage at oriC . ? DnaB protein has helicase activity and it further unwinds the DNA in the prepriming plex in both directions, assisted by DNA gyrase. SSB tetramers coat singlestranded regions as they arise . ③ Primer synthesis: each DnaB activates a DnaG primase, in one case to initiate the leading strand, and in the other to initiate the first Okazaki fragment of the lagging strand. （二）復(fù)制的延伸： 1. 復(fù)制體：酶和相關(guān)蛋白在復(fù)制叉形成的超分子復(fù)合物 2. 先導(dǎo)鏈和后隨鏈的同時(shí)復(fù)制 ? Lagging template strand通過復(fù)制體形成一個(gè)環(huán)狀結(jié)構(gòu)， primase已經(jīng)合成一條引物＃ 2 ? 隨著岡崎片段的合成，環(huán)逐漸變大，直到＃ 2片段末端接近前一岡崎片段的引物 ? 復(fù)制體釋放環(huán)， primase合成一個(gè)新的引物 3. 環(huán)型 DNA的復(fù)制類型： ① θ型（ ） : an origin creates two replication forks that move in opposite directions ② Dloop (mammalian mitochondrial DNA)： ? mtDNA的復(fù)制在 H鏈的復(fù)制起點(diǎn) OH開始合成 。 Key concepts: Mitochondria use different origin sequences ③ Rolling circles（ φX174 phage ） ? A protein nicks the origin and binds to 5’ end. ? Using the rolling circle, the 3 –OH end of the nick is extended into a new chain. ? The positive strand has grown to double length and replication fork is back at the in. ? A protein cuts the boublelength positive strand in half,releasing the displaced half and binds to the new 5’ end. ? Releasd plus strand forms covalent
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