chapter6structureofDNAandRNA.ppt

WelcometoMyMolecularBiologyLecture,MolecularBiologyoftheGene,5/E-Watsonetal.(2004),PartI:ChemistryandGeneticsPartII:MaintenanceoftheGenomePartIII:ExpressionoftheGenomePartIV:RegulationPartV:Methods,PartII:MaintenanceoftheGenome,DedicatedtothestructureofDNAandtheprocessesthatpropagate(传递),maintain(保持)andalter(改变)itfromonecellgenerationtothenext,MaintenanceoftheGenome,Ch6:ThestructuresofDNAandRNACh7:Chromosomes,chromatinsandthenucleosomeCh8:ThereplicationofDNACh9:ThemutabilityandrepairofDNACh10:HomologousrecombinationatthemolecularlevelCh11:Site-specificrecombinationandtranspositionofDNA,PROPAGATEnucleosomesintroducesnegativesupercoilingineukaryotes,Negativesupercoilsserveasastoreoffreeenergythataidsinprocessesrequiringstrandseparation,suchasDNAreplicationandtranscription.StrandseparationcanbeaccomplishedmoreeasilyinnegativelysupercoiledDNAthaninrelaxedDNA,DNATOPOLOGY(3),Function(2):Topoisomerases(P115-119),Thebiologicalimportanceoftopoisomerase?Thefunctionaldifferenceofthetwotypesoftopoisomerases?Theworkingmechanismoftopoisomerase,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,1,2,3,4,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,Thecrystalstructureofa23Sribosome,Function:SomeRNAsareenzymes,RNASTRUCTURE(4),RibozymesareRNAmoleculesthatadoptcomplextertiarystructureandserveasbiologicalcatalysts.RNasePandself-splicingintronsareribozymes,Structure&Function:ThehammerheadribozymecleavesRNAbyformationofa2,3cyclicphophate,RNASTRUCTURE(5),Homework,Playthestructuraltutorial“IntroductiontotheDNAstructure”tobetterunderstandDNAstructure,KeypointsforChapter6,Definitions:topoisomerase,ribozyme,doublehel