现代分子生物学之原核细胞转录PPT学习教案

1、会计学1Principal Types of RNAs Produced in Cells: a particular segment of DNA is copied into RNA by the enzyme RNA polymerase: RNAP, RNA pol第1页/共29页General themes of transcription第2页/共29页Transcription selectively occurs at only certain parts of the genome, and makes a few to thousands copies, transient

2、ly, variably in different cells, in different enviroment.第3页/共29页 RNA Polymerases第4页/共29页Mg 2+第5页/共29页第6页/共29页TerminationInitiationElongation第7页/共29页RNA polymerase binds at specific location: Promoter strength: 第8页/共29页RNA Pol Leaves Its Footprint on a PromoterHow did we identify the promoter in DNA

3、 molecule?第9页/共29页In bacteria, its thefactor that makes RNA polymerase initiate transcription only at promotersC- terminal domainfactorHoloenzymeCore enzymeThefactor has four regions第10页/共29页Two helices within region 4 form a for DNA binding 第11页/共29页An recognizes and interact with bases on non-temp

4、late strand at 10 through its aromatic AAsConformational change, spontaneously but irreversible, in the DNA-enzyme complex to a 第12页/共29页RNA polymerase holoenzyme = + 第13页/共29页RNA polymerase holoenzyme = + + + + + + + + + + + +The region 3-4 linker of sigma factor (RNA mimic) lies in middle of the R

5、NA exit channel in the open complex第14页/共29页RNA polymerase holoenzyme = + 第15页/共29页It opens DNA double helix between -11 and +3第16页/共29页Initial transcription第17页/共29页Initial transcriptionPromoter escape involves breaking polymerase-promoter and the polymerase core-sigma interactionshe region 3-4 lin

6、ker of factor (RNA mimic): the RNAP repeatedly and short RNA products until they reach 10nt, otherwise polymerase is .第18页/共29页The polymerase remains stationary and DNA into itPolymerases active center relative to DNA template and synthesizes short transcripts before aborting-repeating until escapin

7、g the promoterEnergy stored in scrunching is released to promoter escape and dislodging of sigma factor第19页/共29页Transcription shifts into the elongation phase once a short stretch of RNA ( 10 nt) is synthesizedThe transition requires further conformational change in polymerase that leads it to grip

8、the template more firmly第20页/共29页1. in the catalytic cleft2. (Only 8-9 nts remain base-paired with the DNA template at any given time) 3. from the DNA template just behind the RNA pol, then the 第21页/共29页Although proofreading for RNA synthesis do exist, transcription() is less accurate than replicati

9、on(); Pyrophosphorolytic editing: remove a correctly or incorrectly inserted ribonucleotide by reincorporation of PPi, but hover longer over mismatchHydrolytic editing: the enzyme backtracks by one or more nucleotides and removes the error-containing sequence. (stimulated by , which both enhance hyd

10、rolytic editing function and serve as elongation stimulating factors: ensure that polymerase elongates efficiently and help overcome “arrest” at the difficult regions)第22页/共29页The micrograph(under the electron microscope) shows many molecules of RNA polymerasesimultaneously transcribing each of two

11、adjacent genes. Molecules of RNA polymerase are visible as a series of dots along the DNA with the newly synthesized transcripts (fine threads) attached to them.Multiple RNA pol molecules can transcribe the same gene at the same time, each following closely behind another; 第23页/共29页Terminators: the sequences that trigger RNA polymerase to dissociate from the DNARho-independent terminator : a short inverted repeat (20 bp) and a stretch of 8 A:T base pairs. 第24页/共29页Have less well-characterized RNA elements rut ( utilization)Rho binding can wrest