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n. 為什么 DNA的合成需要 RNA引物? 五、旋轉(zhuǎn)酶 (gyrase ): a Type II topoisomerase, acts to overe the torsional stress imposed upon unwinding by introducing negative supercoils at the expense of ATP hydrolysis. ?復制叉前進帶來扭曲張力 ?拓撲異構(gòu)酶 II: 引入負超螺旋 六、 DNA連接酶 ( DNA ligases ) DNA ligase makes a bond between an adjacent 3’OH and 5’ phosphate end where there is a nick in one strand of duplex DNA . 酶活化 AMP轉(zhuǎn)移 3′ OH親核攻擊 第三節(jié) DNA的復制過程 一、原核生物的復制( ) (一)復制的起始: 1. 復制原點: Ori C,含兩個系列的重復單位, 3個 13bp重復序列(富含 AT),和 4個 9bp重復序列(識別位點) 2. 起始過程: ① The origin is initially recognized by DnaA that forms a large plex with DNA. A short region of ATrich DNA is melted. ② DnaB is bound to the plex and creates the replication fork. ③ The