二、 General features of DNA replication DNA复制的基本特征（多数生物） (一) Semiconservative replication DNA的半保留复制 1.definition DNA replication:in which the two strands of a parental duplex separate completely and pair with new progeny strands. One parental strand is therefore conserved in each progeny duplex.DNA复制必须以一条母链为模板以碱基互补的原则合 成新的DNA链，即新合成的DNA双螺旋由一条母链和一条新 合成的 2025/5/15 6
2025/5/15 6 1.definition （一）Semiconservative replication DNA的半保留复制 DNA replication: in which the two strands of a parental duplex separate completely and pair with new progeny strands. One parental strand is therefore conserved in each progeny duplex. DNA复制必须以一条母链为模板以碱基互补的原则合 成新的DNA链，即新合成的DNA双螺旋由一条母链和一条新 合成的子链构成。 二、General features of DNA replication DNA复制的基本特征（多数生物）
2.Hypothesis and evidence of DNA semiconservative replication DNA半保留复制假说的提出及证实： 1)DNA double helix Phosphorus Minor Carbon in groove sugar-phosphate backbone' Hydrogen 3.4nm Oxygen Major groove 0.34nm Bases 二a性☒ 2025/5/15 7
2025/5/15 7 2. Hypothesis and evidence of DNA semiconservative replication DNA半保留复制假说的提出及证实： 1) DNA double helix
2)Three hypotheses for DNA replication 三种DNA复制假说： (a)Semiconservative (b)Conservative (c)Random dispersive 8 Figure 20.1 Three hypotheses for DNA replication
2025/5/15 8 2) Three hypotheses for DNA replication 三种DNA复制假说：
3)Evidence from experiments实验证据： Meselson and Stahl (a) (b) Figure 1.11 (a)Matthew Meselson;(b)Franklin Stahl.(Source:(a) Courtesy Dr.Matthew Meselson.(b)Cold Spring Harbor Laboratory Archives.) They experimentally proved Watson and Crick's model of semi-conservative replication-1958 2025/5/15 9
2025/5/15 9 3) Evidence from experiments 实验证据： Meselson and Stahl They experimentally proved Watson and Crick’s model of semi-conservative replication-1958
15 细菌在含有15N的培养基上生 长多代，使DNA双链充分标记 转入4N培养基中 (a) (b) (c) (a)立即取出 (b)繁殖一代后取出 (b)繁殖二代后取出 提取DNA.CsCI 密度梯度离心 轻带 杂交带 重带 半保留复制证明的实验 Unlabeled Meselson-StahlDNA control 14N4N 双车轻DNA双重DNA 杂交DNA 杂交DNA 双车轻DNA
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