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The importance of DNA replication

The importance of DNA replication. Genomic DNA must be replicated (doubled) before mitosis and meiosis: cell proliferation and gametogenesis. The mutation created in parents can be inherited by offspring via DNA replication. The basis of DNA repair, recombination and transposition

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The importance of DNA replication

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  1. The importance of DNA replication Genomic DNA must be replicated (doubled) before mitosis and meiosis: cell proliferation and gametogenesis. The mutation created in parents can be inherited by offspring via DNA replication. The basis of DNA repair, recombination and transposition The target of drugs for infections disease

  2. DNA的复制 • 一、DNA复制的基本规律 • 二、DNA复制所需的酶和蛋白质 • 三、DNA复制的一般过程 • 四、原核生物和真核生物DNA的复制特点

  3. 复制(replication) • 是指遗传物质的传代，以母链DNA为模板合成子链DNA的过程。 (dNMP)n+ dNTP → (dNMP)n+1+ PPi

  4. 一、DNA复制的基本规律 • 1、半保留复制 　　一个双链DNA分子复制所产生的两个子代双链DNA分子，一条链是新合成的，另一条则来自亲代DNA分子，即子代保留了一条亲本链，因而这种复制方式称为半保留复制。 • 2、半不连续复制 DNA复制过程中，一条子链的复制是连续的，而另一条子链的复制是不连续的，这种复制方式称为半不连续复制。

  5. 1、半保留复制 • 1953年Watson和Crick发表了DNA双螺旋结构模型，同年紧接着提出了DNA半保留复制的机理。 • 1958年，M. Meselson和F. Stahl用大肠杆菌设计精巧的实验证明了半保留复制模型的正确性。

  6. The Meselson and Stahl experiment The Meselson and Stahl experiment to determine　the mode of DNA replication. The bands in the centrifuge tube　are visible under　ultraviolet light. The pattern of bands (left)　comes about from semiconservative DNA replication　(right) of　15N DNA (blue) replicating in a 14N medium (red).

  7. 半保留复制的意义 • 复制的这种方式可保证亲代的遗传特征完整无误的传递给子代，体现了遗传的保守性。

  8. 2、半不连续复制 • DNA复制过程中，新生子链的合成只能沿5’→3’进行。 • 以3’→ 5’模板链进行互补复制时，子链的复制方向与双链的解开方向一致，可持续合成而形成一条连续的互补链，称为前导链。 • 而以5’ → 3’模板链进行互补复制时，子链的复制方向与双链的解开方向相反，不能持续合成，而是先以5’ → 3’方向不连续合成许多小片段，称为冈崎片段，最后再由DNA连接酶将这些冈崎片段连接成一条完整的互补链，称为后随链。

  9. Discontinuous model of DNA replication. Lagging-strand replication requires Okazaki fragments to form　going backward, away from the Y-junction.

  10. 二、DNA复制所需的酶和蛋白质 • 1、DNA聚合酶(DNA polymerase) • 2、引发酶(primase)（合成11-12bp 的RNA片段） • 3、DNA连接酶(DNA ligase) • 4、拓扑异构酶(topoisomerase)(作用于超螺旋） • 5、解链酶(helicase) • 6、单链结合蛋白(single strand binding protein, SSB)

  11. DNA聚合酶 • 共同特点是： • （1）需要提供合成模板； • （2）不能起始新的DNA链，必须要有引物提供3'－OH； • （3）合成的方向都是5’→3’ • （4）除聚合DNA外还有其它功能(修复）。

  12. E.coli 中的三种DNA多聚酶

  13. In E coli, DNA polymerase Ⅲ synthesizes DNA beginning at the RNA primer. On the lagging strand, DNA polymeraseⅠ removes the RNA primer replacing it with DNA. • Proofreading activity achieved through the reverse (3’ →5’) exonuclease activity of DNA polymerase ensures the replication accuracy

  14. 真核的DNA聚合酶 • 真核DNA的复制至少涉及5种复制酶， • 其中α、δ、ε参与染色体DNA的复制， • α与引物酶协作合成RNA引物； • δ是真正的DNA复制酶； • β和ε负责DNA的修复 (3’-5’exonuclease) • γ的功能是线粒体DNA的复制。

  15. 三、DNA复制的一般过程 • 1、 DNA复制的起始 • 2、DNA复制的延伸 • 3、DNA复制的终止

  16. A　Summary of DNA Replication

  17. 四、原核生物和真核生物DNA的复制特点 • 1、复制的起点(replication origin)和速率 　通常原核生物只有一个复制起点，而真核生物基因组中有很多个复制起点。 • 2、复制方式 　原核生物的染色体和质粒DNA都是环状分子，采用θ型复制或滚环复制；哺乳动物的线粒体DNA（环状DNA分子）采用D环复制方式，基因组DNA采用多复制泡线性复制。 • 3、真核生物染色体末端DNA的复制 端粒(telimere)与端粒酶(telomerase)

  18. Replication Origin and Replication Fork Replication origin: replication initiation site, usually contain sequences rich in weak A-T base pairs Replication fork: the region where the helix unwinds and new DNA is synthesized.

  19. 复制叉 (the replication fork）

  20. in eukaryotes, DNA replication is initiated at multiple origins and replication forks proceed in either direction. Form replication bubbles which eventually meet and merge.

  21. DNA Replication Models

  22. DNA Replication Models

  23. DNA Replication Models

  24. 真核生物端粒的复制 • 在真核生物，由端粒酶（telomerase）催化, 在真核线性DNA的末端形成一种特殊的结构并与蛋白质结合成端粒（telomere）。

  25. 端粒由成百个6个核苷酸的重复序列所组成（人为TTAGGG，四膜虫为TTGGGG）。 端粒由成百个6个核苷酸的重复序列所组成（人为TTAGGG，四膜虫为TTGGGG）。 • 端粒的功能为稳定染色体的末端结构，防止染色体间末端连接，并可补偿滞后链5′-末端在消除RNA引物后造成的空缺。 • 复制可使端粒5′末端缩短，而端粒酶（telomerase）可外加重复单位到5′-末端上，结果使端粒维持一定的长度。

  26. video

  27. DNA复制的忠实性 • 在大肠杆菌DNA的复制中，每聚合109-1010个碱基的才出现一个错误 • 1、碱基配对原则 • 2、引物RNA的作用 • 3、DNA聚合酶的校正阅读作用

  28. The importance of DNA replication Genomic DNA must be replicated (doubled) before mitosis and meiosis: cell proliferation and gametogenesis. The mutation created in parents can be inherited by offspring via DNA replication. The basis of DNA repair, recombination and transposition The target of drugs for infections disease

  29. A6 DNA replication

  30. DNA replication • The replication fork • Bacterial DNA replication • DNA replication in eukaryotes

  31. 1. DNA replication • DNA replication is the process by which a cell copies its DNA. DNA polymerases catalyze this reaction, by acting on single-stranded DNA synthesizing a new strand complementary to the original strand. • 是指遗传物质的传代，以母链DNA为模板合成子链DNA的过程。

  32. (dNMP)n+ dNTP → (dNMP)n+1+ PPi

  33. DNA synthesis always in the 5’ →3’ direction. • DNA replication is semi-conservative: copied DNA contains one strand derived from the parent molecule and one newly synthesized strand

  34. DNA的半保留复制模型

  35. The mechanism of DNA replication: very similar in most organisms • In prokaryotes, DNA polymerase Ⅰand Ⅲ • In eukaryotes, five DNA polymerase (αβγδ(delta)ε) • Proofreading activity achieved through the reverse (3’ →5’) exonuclease activity of DNA polymerase ensures the replication accuracy

  36. 2. The replication fork • Replication origin: replication initiation site, usually contain sequences rich in weak A-T base pairs • Replication fork: the region where the helix unwinds and new DNA is synthesized.

  37. 复制起始时打开DNA双螺旋的过程 How to open double helix at initiation stage?

  38. A number of several distinct events occur at this site: • Separation of the double helix: helicase separate the double helix and single-strand binding (SSB) protein attaches to the DNA and prevents the double helix from reforming • Synthesis of leading and lagging strand: leading strand is synthesized continuously, lagging strand discontinuously, a series of Okazaki fragments

  39. 半不连续复制 Semi-discontinuous replication

  40. Priming: primase synthesizes a short RNA primer sequence on the DNA template creating a short double-stranded region required by DNA polymerase to initiate DNA synthesis.

  41. In E coli, DNA polymerase Ⅲ synthesizes DNA beginning at the RNA primer. On the lagging strand, DNA polymeraseⅠ removes the RNA primer replacing it with DNA. In eukaryotes, DNA polymerase αhas internal primase activity.

  42. In eukaryotes, DNA is replicated by DNA polymerase αand δwithαsynthesizing the lagging strand andδsynthesizing the leading strand. DNA polymerase εis involved in DNA repair and DNA polymerase γ replicates mitochondrial DNA.

  43. Ligation: for lagging strand synthesis. Carried out by a DNA ligase enzyme.

  44. DNA合成的起始：先合成一段互补的RNA引物 Initiation of DNA synthesis:a complement RNA primer synthesis

  45. DNA聚合酶III 同时合成前导链和后随链 Concurrent synthesis on leading and lagging strand by DNA Pol III

  46. 发生在复制叉处的DNA合成过程 Summary of DNA synthesis at a single replication fork

  47. 3. Bacterial DNA replication • Circular DNA replication: a single replication origin, two replication forks progress in opposite directions. θ form. Forks meet, fuse and replication terminates. • Supercoiling and topoisomerases: for circular DNA, no free ends, unwinding DNA helix produces supercoiling. To overcome this, topoisomerases are required:

  48. Topoisomerase Ⅰ: produces a transient break in the polynucleotide backbone of one of the DNA strands a short distance ahead of the replication fork. Rejoin the broken ends.

  49. Topoisomerase Ⅱ: cause transient breaks in both strands of one of the DNA molecules allowing the other DNA molecule to pass through, thus separating the two daughter molecules. Rejoin the broken strands.

  50. E. coli DNA复制:θ型 DNA replication of E. coli chromosome: θ type

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