《dna的復(fù)制》ppt課件-文庫吧
2025-04-16 18:05 本頁面
【正文】 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(fù)制叉前進(jìn)帶來扭曲張力 ?拓?fù)洚悩?gòu)酶 II： 引入負(fù)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(fù)制過程 一、原核生物的復(fù)制（ ） （一）復(fù)制的起始： 1. 復(fù)制原點(diǎn)： Ori C，含兩個(gè)系列的重復(fù)單位， 3個(gè) 13bp重復(fù)序列（富含 AT），和 4個(gè) 9bp重復(fù)序列（識(shí)別位點(diǎn)） 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 ATrich DNA is melted. ② Helicase is bound to the plex and creates the replication fork. ③ The first nucleotides of the new chain are synthesized into the primer ① DnaA protein is the initiation factor : ? The four 9 bp consensus sequences on the right side of oriC provide the initial binding sites for DnaA. It binds cooperatively to form a central core around which oriC DNA is wrapped. ? Then DnaA acts at three ATrich 13 bp tandem repeats located in the left side of oriC. In the presence of ATP, DnaA melts the DNA strands at each of these sites to form an open plex ? HU protein has the capacity to bend DNA, and is involved in building the structure that leads to formation of the open plex. ? Transcriptional activation: RNA polymerase could be required to read into the origin from adjacent transcription units. The act of transcription could be associated wi
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