生物RNAtranscription.ppt

Chapter 9: RNA transcription and regulation in prokaryotes Content Central dogma（中心法则） Transcription RNA polymerase the process of prokaryotic transcription 1. Central dogma DNA是生物遗传的主要物质基础。遗传信息以特定的脱氧核苷酸序列储存在DNA分子中。DNA能准确地自我复制，并通过转录把遗传信息传递到mRNA分子上，然后通过mRNA翻译成为具有特定aa顺序的蛋白质，由蛋白质行使各种生物学功能。 补充：反转录病毒可以其RNA作为模板指导合成DNA；某些病毒RNA可以进行自我复制，即以自身RNA为模板，合成子代RNA。 Transcription: the synthesis of RNA under the direction of DNA Transcription is the first and the most important step in the course of gene expression. Whether a gene expressed or not depend on the transcription stage. Transcription Features Asymmetry--我们将用作RNA合成的模板的链叫做反义链；另一条不做模板的链叫有义链。RNA为全保留转录 转录开始不需要引物; 转录的单向性;链的延长方向是 5′→ 3′ 有特定的起始和终止位点 转录和复制：都是遗传信息的传递 RNA polymerase are enzymes that synthesize RNA using a DNA template (formally described as DNA-dependent RNA polymerases). core enzyme α: required for assembly of the core enzyme β: catalyze the formation of phosphodiester bond ； β’ : negative charged, can be crosslinked to the template DNA, the product RNA, and the substrate ribonucleotides ； 4. the process of prokaryotic transcription The transcription reaction can be divided into transcriptional unit , transcriptional initiation, elongation and termination ； From a promoter to a terminator----a transcriptional unit； Transcription is controlled by specific initiation sites called promoters and termination sites called terminators 1) initiation the function of σ factor： σ factor reduces the affinity for sequence-independent binding (about 20000 times), and confers specificity for promoters (about 1000 times) So the RNA extends slowly 2) elongation RNA pol 沿着模板链移动，RNA链不断延伸，并保持三元复合物的结构； 转录泡中的DNA螺旋前开、后合，RNA延长，不断脱离DNA； RNA链的延伸速度不是恒定的，在模板富含GC的区域，转录就会减慢/停顿。 3) Termination A terminator is a sequence of DNA that causes RNA polymerase to terminate transcription； Many terminators require a hairpin to form in the secondary structure of the RNA being transcribed. This indicates that termination depends o