①5'→3'聚合酶 Incoming deoxynucleoside 5'-triphosphate 0=P-0 0 0=P-0 0 5'3 70 0=P-0 0=P-0 0 5® 5'0 Growing 3 0=P-01 OH DNA strand 0 新生链 A G A T A T Template 模板链 3'® P5' 3'P P 6 Deoxyribose
① 5 ´ → 3 ´聚合酶 模板链 新生链 5´ 3´
②3'→5'外切酶活性 DNA polymerase I The mispaired 3'-OH end of the growing DNA polymerase strand blocks further active site elongation.DNA 100日 polymerase slides back 3'5'(proofreading) 01L0010000 to position the exonuclease mispaired base in the active site 3'-→5'exonuclease active site. C removed 5g001 OH Cis a rare tautomeric OH form of cytosine(C*) The mispaired 100 that pairs with A and nucleotide is removed. is incorporated into 000010001 the growing strand. 1010100101000 (unable to pair with A) DNA polymerase slides forward and resumes its polymerization activity. Before the polymerase moves on,the cytosine undergoes a tautomeric shift from C*to C.The 08日 0010000100 new nucleotide is now mispaired
C (unable to pair with A) C removed ② 3 ´ → 5 ´ 外切酶活性
③5'→3'外切酶活性 3 Nick 5 OH RNA or DNA 5 31 3 -51 Template DNA strand DNA polymerase OH 5 3 3 5 dNMPs dNTPs (PPin OH 51 3 Nick OH -3 6
③ 5 ´ → 3 ´ 外切酶活性 3’ 5’
DNA- DNA- DNA- 原核生物 pol I pol I polⅢ 5'→>3'聚合活性 + + + 功 3'→5'外切酶活 + + + 性 5′→3'外切酶活 性 + 分子量 109000 120000 140000 每个菌体中所含的酶分子数 400 40 20 聚合速率（核苷酸数/分/酶） 1000 60000
原核生物 DNApol Ⅰ DNApol Ⅱ DNApol Ⅲ 功 能 5´ 3´聚合活性 + + + 3´ 5´外切酶活 性 + + + 5´ 3´外切酶活 性 + - - 分子量 109 000 120 000 140 000 每个菌体中所含的酶分子数 400 40 20 聚合速率（核苷酸数/分/酶） 1000 60 000
真核生物的DNA聚合酶 DNA-pol a 延长随后链 DNA-polB可能是DNA修复酶 DNA-polY参与线粒体DNA复制 DNA-pol8延长前导链 DNA-pole校读、修复、填补缺口 真核生物中真正负责复制作用：DNA聚合酶-Q,δ
真核生物的DNA聚合酶 DNA-pol α 延长随后链 DNA-pol β 可能是DNA修复酶 DNA-pol γ 参与线粒体DNA复制 DNA-pol δ 延长前导链 DNA-pol ε 校读、修复、填补缺口 真核生物中真正负责复制作用：DNA聚合酶-α，δ