dna的復(fù)制ppt課件-在線瀏覽
2025-06-18 18:05本頁面
【正文】 ，含兩個系列的重復(fù)單位， 3個 13bp重復(fù)序列（富含 AT），和 4個 9bp重復(fù)序列（識別位點） 2. 起始過程： ① The origin is initially recognized by a protein that forms a large plex with DNA. A short region of A ? 當(dāng)置換鏈通過 L鏈的復(fù)制起點 OL時，開始合成新的 H鏈 。 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 circle. 4. Restart of stalled replication forks : ? Initiation of φX174 replication requires the primosome plex to displace SSB from the origin. The primosome consists of six proteins: PriA, PriB, PriC, DnaT, DnaB, and DnaC. A primosome assembles at a unique site, called the assembly site (pas). ? The importance of the primosome for the bacterial cell is that it is used to restart replication at forks that stall when they encounter damaged DNA. ? At forks without a lagging strand, the singlestranded laggingstrand template can be bound directly by DnaB. ? At forks with a lagging strand, this strand must be unwound by PriA helicase to generate a singlestranded binding site for DnaB loading （三）、復(fù)制的終止： 1. 環(huán)形 DNA： ① 單向復(fù)制：復(fù)制終點＝復(fù)制起點 ② 雙向復(fù)制：兩個生長點的簡單碰撞 (無固定 終點 ) 有固定終點（如 ） Ter終止位點 當(dāng)復(fù)制叉前移，遇到 20bp重復(fù)性終止子序列（ Ter
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