七年制分子生物复习

Replication复制,transcription转录andtranslation转移Questions:1.Whatissemi-discontinuousreplication?TheleadingstrandcopiescontinuouslyThelaggingstrandcopiesinsegments(Okazakifragments)whichmustbejoined2.WhichenzymesandproteinparticipateinDNAsynthesis?Whatfunctionsdotheyexertinthereplicationprocess?原核InitiationofReplication：1）DnaAisareplicationinitiationfactorwhichpromotestheunwindingofDNAatoriCduringDNAreplicationinE.coli.2）DnaB(helicase)movesalongaDNAstrandopeninguptheduplextomeltandseparatetheDNAstrands.bindtoDnaGinitiatingprimersynthesis.3）Single-strandedbindingproteins(SSBs)stabilizesingle-strandedDNA，preventfromreannealing(不覆盖碱基，不影响ssDNA作为复制模板)4）DnaG(Primase)catalyzessynthesisofshortRNAmoleculesthatfunctionasprimersforDNAsynthesisinE.coli.PrimasebindstoDnaBproteinatoriCandformsaprimosome.（可在随从链中移动）5）TypeItopoisomerasecutsonestrandofaDNAdoublehelix,relaxationoccurs,andthenthecutstrandisreligeted.TypeIItopoisomerasecutsbothstrandsofoneDNAdoublehelix,passesanotherunbrokenDNAhelixthroughit,andthenreligetesthecutstrands.TopoisomeraseremovessupercoilsproducedbyDNAunwindingatthereplicationforkElongationofReplication：1）DNApolymerase:TheenzymesthatreplicateDNA.TheincomingbaseisselectedwithintheDNApolymerasesactivesite.Chaingrowthisinthe5’to3’direction.TherearemanydifferenttypesofDNApolymerasePolymerasePolymerization(5’-3’)Exonuclease(3’-5’)Exonuclease(5’-3’)IYesYesYesIIYesYesNoIIIYesYesNoPolI:GapfillingduringDNAsynthesisandrepair,removalofRNAprimersPolII:InvolvedinDNAsynthesisofdamagedtemplatesPolIII:FunctionalpolymeraseatthereplicationforkPolI:GapfillingduringDNAsynthesisandrepair,removalofRNAprimersPolII:InvolvedinDNAsynthesisofdamagedtemplatesPolIII:FunctionalpolymeraseatthereplicationforkTerminationofReplication:1）RNAse:removeRNAprimers2）DNApolymeraseI:TheRNAprimerisremoved(thelastnuclotide)andreplacedwithDNAbypolymeraseI3）DNAligase:sealsthegapsbetweenOkazakifragmentswithaphosphodiesterbond真核：1）DNApolymerasesineukaryoticcellsα→hasaprimasesubunitandfunctionsininitiationssynthesizestheRNAprimersandastretchofDNAsequences,hasnoproofreadingactivity.δ→theprincipalDNApolymeraseineukaryoticcellshasproofreadingactivity.ε→itsprecisefunctionisunclear;sensorforDNAdamagecheckpointcontrolβ→DNArepairγ→mitochondrialDNAreplication2）RPA(replicationproteinA)bindstothemeltedsingle-strandedDNA.3）RFC(replicationfactorC)RFCistheeukaryoticcounterpartoftheprokaryoticγ-3）PCNA(proliferatingcellnuclearantigen,similartoeukaryoticslidingDNAclamp)displacesPola-primase.ItcanclampDNApolymeraseδtotheDNA.4）Tantigen：Itisamultifunctionalsite-specificDNAbindingproteinencodedbySV40DNA,bindstotheorigin(asDnaA)andmeltstheduplexDNA(asDnaB)Prokaryoticvs.EukaryoticcellsReplicationEnzymes：ProkaryoticeukaryoticDnaBHelicaseHelicase[T-Ag(SV40)]SSBRPAγ-ComplexClampLoaderRFCSlidingClampPCNAPrimase(DnaG)Prima3.PleasedescribetheprocessofDNAsynthesis.原核inE.coli:1)DnaAproteinbindstothe'9-mer'regioninoriCandformingamultimericcomplexwith10-20proteinsubunits.BindingrequiresATP.2)FurtheradditionofATPwasobservedtoresultinameltingandopeningupoftheDNAduplexintheoriCregion.3)Afterhelicase/DnaCbindstotheDNA,thednaCproteinisreleased.4)Single-strandedDNA-binding(SSB)proteinsstabilizethesingle-strandedtemplateDNAduringtheprocess.5)DNAprimasenextbindstohelicaseproducingacomplexcalledaprimosomePrimasesynthesizesashortRNAprimer,towhichDNApolymeraseIIIaddsnucleotides.6)PolymeraseIIIaddsnucleotides5’to3’onbothstrandsbeginningattheRNAprimer.τ-protein:使helicase夹紧γcomplex(clamploader):loadslidingclamponDNAstrandSlidingclamp:固定识别为点，使DNApol与DNA有高亲和力7)TheRNAprimerisremovedandreplacedwithDNAbypolymeraseI,andthegapissealedwithDNAligase.真核：ModelofinvitroreplicationofSV40DNAbyeukaryoticenzymes:1）Tantigen(Tag)bindsandunwindsreplicationorigin;2）RPAbindstosingle-strandedDNA;3）Polα-primasesynthesizestheprimers(RNA+DNA).4.）RFCloadsPCNAtothetemplate.5.）PCNAdisplacesPolα-primaseandfunctionsasaDNAclamp;6）PolδreplacesPolα-primaseandfurtherextendstheDNAstrands.4.Whatisthemeaningofwobblebasepairingandanswerthemannerofbasepairing?5.Trytocomparethedifferencesandsimilaritiesbetweenthetranscriptionandtranslation.Similaritybetweenreplicationandtranscription:1)BothprocessesuseDNAasthetemplate.2)Phosphodiesterbondsareformedinbothcases.3)Bothsynthesisdirectionsarefrom5´to3´.Differencesbetweenreplicationandtranscription:A-U,T-A,G-CA-T,G-CbasepairssRNAdsDNAproductRNApolymeraseDNApolymeraseEnzymenoyesprimerNTPdNTPsubstratesinglestranddoublestrandstemplatetranscriptionreplication6.DescribeE.coliRNApolymerase.1)RNApolymerasesperformsessentiallythesamereactioninallcells.2)BacteriahaveonlyasingleRNApolymeraseswhileineukaryoticcellstherearethree:RNAPolI,IIandIII3)Holoenzyme（全酶）=σfactor+coreenzymeThecoreenzymealonesynthesizesRNAσfactor:Recognisepromoter,initiatestranscriptiononlyatpromoters.进入延长阶段后与coreenzyme解离（全酶的不同是因为σ亚基的不同）coreenzyme:ααββ’ωββ’:fixDNAstrandtogetherwithpolαα:decidewhichgeneistobetranscriptedω:unclear7.Pleasedescribetheprocessoftranscriptioninprokaryotes.1)Transcriptioninitiation：在起始点附近解旋，从起始点开始转录Transcr