Chapter10Transcriptioninprokaryotes例析.pptVIP

Chapter 10 Transcription in prokaryotes Outline 10.1 Introduction 10.2 Transcription and translation are coupled in bacteria 10.3 Mechanism of transcription 10.4 Historical perspective: the Jacob–Monod operon model of gene regulation 10.5 Lactose (lac) operon regulation 10.6 Mode of action of transcriptional regulators 10.7 Control of gene expression by RNA 10.1 Introduction A central event in gene expression is the copying of the sequence of the template strand of a gene into a complementary RNA transcript. All cells have at least one kind of RNA polymerase – the enzyme that transcribes RNA from DNA – and the machinery that translates the mRNA into protein. The biochemistry of transcript formation is straight forward, but the regulatory mechanisms that have been developed by organisms to control transcription are complex and highly variable. This chapter focuses on the process of transcription in prokaryotes. Some of the similarities and differences between prokaryotes and eukaryotes are pointed out in this chapter, 关于DNA和RNA的碱基序列，方向总是从5’到3’，除非特别说明。对于DNA，一般总是讲编码链上的序列,这样也容易将DNA序列直接与氨基酸的密码子联系起来. RNA转录的一般特点 ☆ 具有选择性，即只对基因组或DNA分子中的编码区进行转录 ☆ 开始于特定位点，并在特定的终点处终止 ☆ 催化转录反应的是RNA聚合酶 ☆ 被转录的DNA双链中只有其中一股模板链作为RNA合成的模板 ☆ 启动子控制起始 ☆ 底物为4种5’-核糖核苷三磷酸 ☆ 合成方向5′- 3′ 10.2 Transcription and translation are coupled in bacteria 10.3 Mechanism of transcription Using DNA as a template, the RNA polymerase polymerizes nucleoside triphosphates (NTPs) by phosphodiester bonds from 5′to 3′. In bacteria such as Escherichia coli, there is one type of RNA polymerase, while eukaryotes have multiple nuclear DNA-dependent RNA polymerases and organelle-speci?c polymerases. cis-acting sequence or element(顺式作用元件) 又称分子内作用元件，指存在于DNA分子上的 一些与基因转录调控有关的特殊顺序。 在原核生物中，大多数基因表达通过操纵子模型 进行调控，其顺式作用元件主要由启动基因、操纵 基因和调节基因组成。 在真核生物中，与基因表达调控有关的顺式作用 元件主要有启动子（promoter）、增强子（enhancer） 和沉默子（silencer）。 trans-acting factor（反式作用因子）又称为 分子间作用因子，指一些与基因表达调控 有关的蛋白质因