Dictation 3 3 Dictation test 3 3 25

Dictation 3 / 听写 3 Dictation test 3 / 听写测验3 25 vocabularies of chapters 7 to 9 第 7章至第 9章的25个词汇。 1 / 42

Better City, Better Life / 城市，让生活更美好 2 / 42

How is DNA innovated? / 如何创新DNA？ Chapter 1 – Proteins are very important Chapter 2 – DNA stores information Chapter 3 – Transcription in prokaryotes Chapter 4 – Transcription in eukaryotes Chapter 5 – m. RNA modifications in eukaryotes Chapter 6 – Translation Chapter 7 – Regulation of gene expression Chpater 8 – DNA replication Chapter 9 – Mutations and mutation repair Better DNA, Better Life! 更好的DNA, 更好的生活! 3 / 42

Lecture 26 Chapter 10 Recombination 第 10章 重组 10. 1 Homologous Recombination 10. 1 同源重组 10. 1. 1 Mechanism for Crossing-Over 10. 1. 1 交换机理 10. 1. 2 Mechanism for Double- 10. 1. 2 双链断裂 Stranded Break Repair 修复机理 10. 1. 3 The Rec. BCD pathway 10. 1. 3 Rec. BCD途径 10. 1. 4 Gene Conversion 10. 1. 4 基因转换 10. 2 Non-homologous Recombination 4 / 42 10. 2 非同源重组 10. 2. 1 Transposons 10. 2. 1 转座子 10. 2. 2 Retrotransposons 10. 2. 2 反转录转座子 10. 2. 3 Bacteriophage λ integration 10. 2. 3 λ噬菌体的整合

Questions for Lecture 26 Q 1 → What is homologous recombination? 什么是同源重组？ Q 2 → Why can homologous recombination innovate DNA? 为什么同源重组能创造新的DNA？ Q 3 → What is Rec. BCD pathway? 什么是Rec. BCD途径？ 5 / 42

Vocabulary of Lecture 26 homologous recombination transposition diploid allele crossing-over heteroduplex meiosis mitosis synapsis 6 / 42 (1/2) 同源重组 转座 二倍体 等位基因 交叉 异源双链 减数分裂 有丝分裂 （染色体）联会

Vocabulary of Lecture 26 Holliday junction holiday branch migration resolution chromatid gene conversion 7 / 42 (2/2) Holliday接头 节日，假日 分支迁移 拆分，解决（方案） 染色单体 基因转换

Q 1 → What is homologous recombination? 什么是同源重组？ 8 / 42

A 1 → 10. 1 Homologous Recombination 同源重组 Homologous recombination: Recombination between DNA molecules with similar DNA sequences. 9 / 42 同源重组：在具有相似 DNA序列的DNA分子之 间发生的重组。

Sexual reproduction of a diploid organism 二倍体生物的有性繁殖 10 / 42

If the chromosomes were unchanged … 如果染色体没有变化. . . Identical Child Grandchild 11 / 42

Crossing-over in meiosis 减数分裂时发生交换 Different Child Grandchild 12 / 42

Homologous Recombination in DNA repair 同源重组在DNA修复中的作用 Homologous chromosomes 13 / 42

Q 2 → Why can homologous recombination innovate DNA? 为什么同源重组能创造新的DNA？ 14 / 42

10. 1. 1 Mechanism for Crossing-over 交换机理 Crossing-over: A recombinational event in which regions of DNA are exchanged between homologous chromosomes. 15 / 42 交换：DNA区域在 同源染色体之间发 生交换的重组事件。

Mechanism of recombination in yeast (1/2) 联会：形成暂 时的碱基对 16 / 42

Mechanism of recombination in yeast (2/2) 17 / 42 Holliday junctions

Branch migration of Holliday junctions Holliday交叉的分支迁移 交叉能够移动并增加两条染色体之间的杂交区域 18 / 42

Resolution of the Holliday junction Holliday交叉的拆分 Resolution of the Holliday junction to create a crossover 产生交换的Holliday交叉拆分 Resolution of Holliday junctions for non-crossover 不产生交换的Holliday交叉拆分 19 / 42

A 2 -1 → Resolution of the Holliday junction to create a crossover 产生交换的Holliday交叉拆分 S 20 / 42

A 2 -2 → Resolution of Holliday junctions for non-crossover 不产生交换的Holliday交叉拆分 Why is this called non-crossover? 22 / 42

Q 3 → What is Rec. BCD pathway? 什么是Rec. BCD途径？ 原核生物大肠杆菌中的同源重组 Rec. BCD Enzyme 23 / 42 http: //labs. fhcrc. org/gsmith/

A 3 → 10. 1. 3 The Rec. BCD Pathway Rec. BCD途径 Rec. BCD pathway: The major homologous recombination pathway in E. coli, initiated by the Rec. BCD protein. Rec. BCD途径：大肠杆 菌中一种由Rec. BCD蛋 白启动的主要的同源重 组途径。 Rec. BCD protein: The protein that nicks one of the DNA strands at a chi site to initiate homologous recombination in E. coli. Rec. BCD蛋白：大肠杆 菌中能在DNA的χ位点 产生切口的蛋白质。 24 / 42

The Rec. BCD Pathway (1/3) 25 / 42

The Rec. BCD Pathway (2/3) 26 / 42

The Rec. BCD Pathway (3/3) 27 / 42

Now showing Meselson-Radding Heteroduplex Model 28 / 42 File: biophoto 7 Introduction to Genetic Analysis Meselson-Radding heteroduplex Model

Homologous Recombination (1/6) Crossing-over occurs between nonsister chromatids（染色单体） of homologous chromosomes. Here we focus on the nonsister chromatids at the DNA level, to describe the Meselson-Radding model of crossing-over. 29 / 42

Homologous Recombination (2/6) First, an endonuclease makes a singlestranded cut in one chromatids. DNA synthesis follows the nicked strand. 30 / 42

Homologous Recombination (3/6) The displaced strand invades the second chromatids, looping out the homologous stretch of DNA. The loop is excised. The remaining free ends are ligated, resulting in a Holliday junction. 31 / 42

Homologous Recombination (4/6) A distinguishing feature of this model is asymmetry, since only one of the two DNA molecules has a heteroduplex region. Sometimes, however, the junction migrates, resulting in two heteroduplexes. 32 / 42

Homologous Recombination (5/6) The junction can be resolved in two ways. Opposite strands cleave and rejoin along either a horizontal or vertical line. 33 / 42

Homologous Recombination (6/6) Strand exchange has occurred in both cases. Examining flanking markers outside the heteroduplex regions reveals that only the vertical resolution generates a whole DNA double-helix crossover. 34 / 42

Now showing again 35 / 42

Essentials of Lecture 26 / 第 26讲要点 A 1 → Homologous Recombination 同源重组 A 2 -1 → Resolution of the Holliday junction to create a crossover 产生交换的Holliday交叉拆分 A 2 -2 → Resolution of Holliday junctions for non-crossover A 3 → 36 / 42 不产生交换的Holliday交叉拆分 The Rec. BCD Pathway / Rec. BCD途径

A 1 → 10. 1 Homologous Recombination 同源重组 Homologous recombination: Recombination between DNA molecules with similar DNA sequences. 37 / 42 同源重组：在具有相似 DNA序列的DNA分子之 间发生的重组。

A 2 -1 → Resolution of the Holliday junction to create a crossover 产生交换的Holliday交叉拆分 S 38 / 42

A 2 -2 → Resolution of Holliday junctions for non-crossover 不产生交换的Holliday交叉拆分 Why is this called non-crossover? 39 / 42

A 3 → 10. 1. 3 The Rec. BCD Pathway Rec. BCD途径 Rec. BCD pathway: The major homologous recombination pathway in E. coli, initiated by the Rec. BCD protein. Rec. BCD途径：大肠杆 菌中一种由Rec. BCD蛋 白启动的主要的同源重 组途径。 Rec. BCD protein: The protein that nicks one of the DNA strands at a chi site to initiate homologous recombination in E. coli. Rec. BCD蛋白：大肠杆 菌中能在DNA的χ位点 产生切口的蛋白质。 40 / 42

Lecture 27 Chapter 10 Recombination 第 10章 重组 10. 1 Homologous Recombination 10. 1 同源重组 10. 1. 1 Mechanism for Crossing-Over 10. 1. 1 交换机理 10. 1. 2 Mechanism for Double- 10. 1. 2 双链断裂 Stranded Break Repair 修复机理 10. 1. 3 The Rec. BCD pathway 10. 1. 3 Rec. BCD途径 10. 1. 4 Gene Conversion 10. 1. 4 基因转换 10. 2 Non-homologous Recombination 10. 2 非同源重组 10. 2. 1 Transposons 10. 2. 1 转座子 10. 2. 2 Retrotransposons 10. 2. 2 反转录转座子 10. 2. 3 Bacteriophage λ integration 10. 2. 3 λ噬菌体的整合 41 / 42

Questions for Lecture 27 Q 1 → What is gene conversion? 什么是基因转换？ Q 2 → What are transposons? 什么是转座子？ Q 3 → What are retrotransposons? 什么是反转录转座子？ 42 / 42