Transcription:BiosynthesisofRNAs5theditionbyHarveyLodish,MatthewP.Scott,PaulMatsudaira,andJamesDarnell4theditionbyHarveyLodish,ArnoldBerk,S.LawrenceZipursky,andPaulMatsudairaLehningerPrinciplesofBiochemistry,FourthEditionBiochemistry5theditionJeremyM.Berg,LubertStryer,andJohnL.TymoczkoOutline•Transcription:thereaction•Transcriptionineukaryotes–Transcriptioninitiation–Transcriptionfactors:regulationofgeneexpression–mRNAprocessing–mRNAstability–Geneprediction•Transcriptioninprokaryotes–Differencesbetweeneukaryotesandprokaryotes–RNApolymeraseinE.coli–Operons–RegulationofgeneexpressioninprokaryotesFertilizedegg8-cellembryo~100trillioncellseachItwasinthispub,EaglepubinCambridge,JamesWatsonandFrancisCrickannouncedtheirdiscoveryofDNAonFebruary28,1953.19531993“Wehavediscoveredthesecretoflife!”TranscriptionTranslationCentraldogmaReversetranscriptionTranscriptionTranslationDNAProteinRNAItwasfirstproposedbyFrancisCrickin1958andre-statedinaNaturepaperpublishedin1970:Transcription:thereactionRNAsynthesisinvolves:1.SeparationoftheDNAstrands;2.UsingoneoftheDNAstrandsastemplate;3.SynthesisofanRNAmoleculeinthe5'to3'directionbyRNApolymeraseusingA,G,CandU;4.Noprimersneeded;5.Noproofreading;6.Incomplementarybasepairing,A,T,G,andConthetemplateDNAstrandspecifyU,A,C,andG,respectively,ontheRNAstrandbeingsynthesized.PolyploidchromosomesinDrosophila•IfourstrandsofDNAwerestretchedoutinaline,the46chromosomesmakingupthehumangenomewouldextendmorethantwometers.•Thehumangenomecontainsmorethan3.3billionbasepairsbutonlyabout30,000genes.Question:Howcancellsfindtherightsitesonthechromosomestostartranscription,howlongtogoandwheretostop?RNAsynthesis•Likeallbiologicalpolymerizationreactions,RNAsynthesistakesplaceinthreesteps:initiation,elongationandtermination.•Initiation:tosearchthegenomicDNAforinitiationsites,alsocalledpromotersites.(Forexample,E.coligenomicDNAhasabout4.6millionbasepairsand2000promoters.)Cellsmusthaveamechanismtoknowwheretostartthetranscription.Althoughgeneexpressi...
