第11章DNA的复制、修复和重组-DNATranscr.ppt

DNATranscription,BasicfeaturesCommontoDNAreplication1)Template,UnwindingandTorsion-relievingarenecessary;2)Proceedonlyinthe53direction;UncommontoDNAreplication1)Noneedforprimers2)NTPsinsteadofdNTPs;UTPinsteadofdTTP3)Lackingproof-readingactivity(errorrateis1in104or105ntsadded)4)Specificregions(notallDNAsequence)canbetranscribed5)Toaspecificgene,onlyonestrandcanbetranscribedRemembersomenomenclatureconventions,RNA合成与DNA合成的比较：,第十三章RNA的代谢,（1）催化方向均是53，延伸的机理相同：反应受焦磷酸水解趋动，需要模板。,（2）RNA合成不需引物（自身可以独立起始合成），且无外切酶作用（即缺乏核对能力）；DNA复制是一个半保留复制，RNA合成是全保留的（因是单链）。,（3）RNA合成起始和终止均受严格的控制，而DNA的终止无特殊的信号。,CentralDogma,Transcription,Translation,Replication,Replication,Retro-transcription,Geneexpression,第一节依赖DNA的RNA合成转录的概念,以DNA分子中的某一区段的一条链为模板，在RNA聚合酶的作用下合成一段RNA链。,53：CodingstrandP324,35：Templatestrand,Codingstrand,Sensestrand,Crickstrand,Templatestrand,antisensestrand,Watsonstrand,Transcription,Translation,原核生物的RNA聚合酶P324,1.亚基的生成,2.功能：催化RNA的合成:tRNA，rRNA，mRNA,3.抑制剂：利福平rifampicin,DNA-DependentRNAPolymerases-RNAP,CommonfeaturesRNAPDNA+NTPs/Mg2+DNA+RNAs+nPPi2nPiDifferencesbetweenDNAPandRNAPProkaryoticRNAPEukaryoticRNAPsViralRNAPs,AllRNApolymerasesrequire:,1)DNAtemplate:onestrandiscopied2)substrateNTPs(GTP,CTP,UTP,ATP)3)divalentcation(Mg2+),DifferencesBetweenDNAPandRNAP,1)RNAPcaninitiatetranscriptiondenovo(i.e.RNAPdoesntneedaprimer!)2)RNAPhasnoproofreadingactivity(errorrateis1in104or105ntsadded)3)RNAPincorporatesNTPsinsteadofdNTPs4)RNAPincorporatesUTPinsteadofdTTP,RNAPinProkaryotes,1)StructureandFunctionAllthreeclassesofRNAsaretranscribedbythesameRNApolymeraseInE.coli,RNAPis465kDcomplex,with2,1,1,1(holoenzyme)Coreenzymeis2,1,1(cantranscribebutitcantfindpromoters)recognizespromotersequencesonDNA2)InhibitorsRifampicin(利福霉素)requiresionsandaG-nuc(GTP,GDP,GMP,GR)anddoesntrequireanyproteinsL-19RNAenzymaticactivities1)NucleotidyltransferaseorRNApolymerase2)Endoribonuclease;RNAligase;Phosphatase,Intron,Exon1,Exon2,Post-transcriptionalprocessingofpre-tRNA,InProkaryotes1)Cleavageandtrimming2)Modification3)AdditionofCCA(ifnecessary)Ineukaryotes1)Cleavageandtrimming2)Modification3)AdditionofCCA4)Splicing(someeukaryotes),RNaseP-Atrueribozyme,Discoverer-SidneyAltman(1989NobelPrizeLaureateinChemistry)StructureandFunction1)Anendonucleaseinvolvedin5-endprocessingofpre-tRNA2)E.coliRNaseP:14-kDapolypeptide+a377-nucleotideRNA(M1RNA).3)AthighMg2+concentrations,isolatedM1RNArecognizesandcleavesE.colipre-tRNAs.TheRNasePpolypeptideincreasestherateofcleavagebyM1RNA,allowingittoproceedatphysiologicalMg2+concentrations.,RNAsthatfunctionasenzymes,Types1)RNaseP2)GroupIintrons(Foundinpre-rRNAsfromsomesingle-celledorganisms,inmitochondrialandchloroplastpre-rRNAs,inseveralpre-mRNAsfromcertainE.colibacteriophages,andinsomebacterialtRNAprimarytranscripts)3)GroupIIintrons(Foundincertainmitochondrialandchloroplastpre-mRNAs)4)23SrRNA:peptidebondformation5)Hammerheadribozymes(someplantviruses)6)snRNAsinvolvedinsplicingFeaturesSignificance“RNAworld”,Whowasproducedfirst,DNAorProtein？,RNA，RNA，RNARNA，RNA，RNA，RNARNA，RNA，RNARNA，RNA，RNA,RNAworld,DNA,Protein,Retro-transcription,Discovery1960s:HowardTeminknewthatretrovirusgenomeswerecomposedofRNAandobservedthatreplicationwasinhibitedbyactinomycinDthereforeheproposedtheconceptofreversetranscription(NobelprizeawardedtoBaltimoreandTemin,1975).1970:TeminandDavidB