武汉大学 分子生物学全部课程 3.ppt

WelcomeEachofYoutoMyMolecularBiologyClass,MolecularBiologyoftheGene,5/E-Watsonetal.(2004),PartI:ChemistryandGeneticsPartII:MaintenanceoftheGenomePartIII:ExpressionoftheGenomePartIV:RegulationPartV:Methods,3/08/05,PartII:MaintenanceoftheGenome,DedicatedtothestructureofDNAandtheprocessesthatpropagate,maintainandalteritfromonecellgenerationtothenext,MaintenanceoftheGenome,Ch6:ThestructuresofDNAandRNACh7:Chromosomes,chromatinsandthenucleosomeCh8:ThereplicationofDNACh9:ThemutabilityandrepairofDNACh10:HomologousrecombinationatthemolecularlevelCh11:Site-specificrecombinationandtranspositionofDNA,3/08/05,CHAPTER6,TheStructuresofDNAandRNA,HowdothestructuresofDNAandRNAaccountfortheirfunctions?,OUTLINE,1.DNAStructure,2.DNATopology,3.RNAStructure,DNASTRUCTURE,DNASTRUCTURE(1),DNAiscomposedofpolynucleotidechains,Structure:twistingaroundeachotherintheformofadoublehelix.,Schematicmodel,Space-fillingmodel,Nucleosidenucleosomesintroducesnegativesupercoilingineukaryotes,Negativesupercoilsserveasastoreoffreeenergythataidsinprocessesthatrequirestrandseparation,suchasDNAreplicationandtranscription.StrandseparationcanbeaccomplishedmoreeasilyinnegativelysupercoiledDNAthaninrelaxedDNA,DNATOPOLOGY(3),Function(2):Topoisomerases(P115-119),Thebiologicalimportanceoftopoisomerase?Thefunctionaldifferenceofthetwotypesoftopoisomerases?Theworkingmechanismoftopoisomerase(Seetheanimationfordetail),DNATOPOLOGY(4),RNASTRUCTURE,RNASTRUCTURE(1),RNAcontainsriboseanduracilandisusuallysingle-stranded,BiologicalrolesofRNA,RNAisthegeneticmaterialofsomevirusesRNAfunctionsastheintermediate(mRNA)betweenthegeneandtheprotein-synthesizingmachinery.RNAfunctionsasanadaptor(tRNA)betweenthecodonsinthemRNAandaminoacids.RNAservesasaregulatorymolecule,whichthroughsequencecomplementaritybindsto,andinterfereswiththetranslationofcertainmRNAs.SomeRNAsareenzymesthatcatalyzeessentialreactionsinthecell(RNasePribozyme,largerRNA,self-splicingintrons,etc).,Structure(1):RNAchainsfoldbackonthemselvestoformlocalregionsofdoublehelixsimilartoA-formDNA,RNASTRUCTURE(2),hairpin,bulge,loop,RNAhelixarethebase-pairedsegmentsbetweenshortstretchesofcomplementarysequences,whichadoptoneofthevariousstem-loopstructures,SometetraloopsequencecanenhancethestabilityoftheRNAhelicalstructures,Forexample,UUCGloopisunexpectedlystableduetothespecialbase-stackingintheloop,PseudoknotsarecomplexstructureresultedfrombasepairingofdiscontiguousRNAsegments,Figure6-32Pseudoknot.,Non-Watson-CrickG:UbasepairsrepresentadditionalregularbasepairinginRNA,whichenrichedthecapacityforself-complementarity,Figure6-33G:Ubasepair,ThedoublehelicalstructureofRNAresemblestheA-formstructureofDNA.,Theminorgrooveiswideandshallow,butofferslittlesequence-specificinformation.Themajorgrooveissonarrowanddeepthatitisnotveryaccessibletoaminoacidsidechainsfrominteractingproteins.ThusRNAstructureislesswellsuitedforsequence-specificinteractionswithproteins,Structure(2):RNAcanfoldupintocomplextertiarystructures,RNASTRUCTURE(3),RNAhasenormousrotationalfreedominthebackboneofitsnon-base-pairedregions,Why?,Interactionsinthetertiarystructure,Unconventionalbasepairing,suchasbasetriples,base-backboneinteractionsProteinscanassisttheformationoftertiarystructuresbylargeRNAmolecule,Thecrystalstructureofa23Sribosme,Function:SomeRNAsareenzymes,RNASTRUCTURE(4),RibozymesareRNAmoleculesthatadoptcomplextertiarystructureandserveasbiologicalcatalysts.RNasePandself-splicingintronsareribozymes,Structure&Function:ThehammerheadribozymecleavesRNAbyformationofa2,3cyclicphophate,RNASTRUCTURE(5),Seeanimationfordetail,Homework(ontheCD),SeetheanimationsforDNAtopology,Topoisomerase,aswellasRibozymeStructureandActivity.Answeringthequestionsin“applyingyourknowledge”isrequired.Playthestructuraltutorial“IntroductiontotheDNAstructure”tobetterunderstandDNAstructureFinishallthecriticalthinkingexercise,KeypointsforChapter6,Definitions:topoi