中南大学 生物化学 考研课件 ch30-33 信息传递 Information Transfer

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1、InformationTransfer(inprocaryotes)ForSpecialtyofBiotechnologyorBioengineeringatCSUMr.XIAJinlanContentDNAreplicationTranscriptionandtheregulationofgeneexpressionProteinsynthesisInformationtransferflowDNAreplicationinprokaryotesMainpointsReplicationstartsatasingl

2、eoriginReplicationisbi-directionalandsemi-conservativeEachreplicationbubble(oreye)consistsoftworeplicationforksGrowthatthereplicationforksisdiscontinuousProteinsinvolvedinDNAreplicationPrimasePolymeraseI(PolI),PolII,PolIIILigasehelicaseReplicationisbidirectiona

3、lUnidirectionalreplicationhasbeenobservedonlyinbacteriophagesandsomeplasmidsp988ReplicationissemidiscontinuousOkazakifragments冈崎片段p989Thegeneralreaction:(DNA)nresidues+dNTP(DNA)n+1+PPiRequirementsforDNAsynthesisPolymeraseI(orpolymeraseIII+polymeraseI)AllfourdN

4、TPsMg2+ADNAtemplateAprimer启动子withafree3’-OHDNAreplication:overviewRequirementsforDNAsynthesisBasicprocedureofDNAreplicationPrimerbindstotheDNAtemplatestrandbybasepairingprinciplePolymeraseIrecognizesthenucleotideAontheDNAtemplatestrandPolymeraseIdirectsthenucle

5、otideT(pairingtoA)3’-OHoftheprimernucleophilicattackstothea-phosphategroupoftheincomingnucleotideTheprimerextendsina5’to3’directionChainelongationreactioncatalyzedbyDNApolymeraseDNApolymerases---theenzymesofDNAreplicationinprocaryotesPropertiesPolIPolIIPolIIIPo

6、lymerization5’→3’√~20bases√√>4.6MegaBasesExonuclease3’→5’√√√Exonuclease5’→3’√××DNApolymeraseIandIIfunctionprincipallyinDNArepair;DNApolymeraseIIIisthechiefDNA-replicatingenzymep9913’→5’exonucleaseactivityofDNApolymeraseITocorrectthemismatchedbasesfrom3’endThe5’

7、3’exomucleaseactivityofDNApolymeraseIRemovetheRNAprimerfrom5’endNickfillingGeneralfeaturesofareplicationforkFigure30.15onp997Pleasefindwhatkindsenzymesareincluded.WherearetheOkazakifragmentsandlaggingstrand?Wherearetheleadingstrand?Concept-checkpointsTowhichend

8、ofanewlysynthesizedstrandofDNAdoespolymeraseaddabase?WhyisaprimerrequiredforDNAreplication?Whataretheleadingandlaggingstrands?Whatisthefunctionofprimer?Whatarethedifferences