交大微生物课件lecture7-3essentials of molecular biology

PrinciplesofMicrobialMolecularBiologyChapter15BROCKBIOLOGYOFSchoolofLifeScienceandTechnologyShanghaiJiaoTongUniversity IV.IV.mRNA WhydoweneedamessengerRNA?Thegeneticinformationneedstoberead“onesentenceatatime”,justlikewespeakinGenesare“sentences”ingeneticProteinsynthesistakesceawayfromwherechromosomeexistsShanghaiJiaoTongOverviewof.1RNARNApolymeraserequiresDNAasatemteDirection:5’3’.Donotneedprimer:RNApolymerasecanstartchainsTriphosphate-containing:TheinitialnucleotideinanRNAretains3ThefirstbaseintheRNAisalwaysapurine.FLASHShanghaiJiaoTongStepsinRNAsynthesis1:TheTheinitiationandterminationsitesarespecificnucleotidesequencesontheDNA.初始化位点与终止点为特定序列TheThesigmafactorallowsRNApolymerasetorecognizetheinitiationsiteStepsinRNAsynthesis2:TheThesigmafactorisduringElongationElongation:RNApolymerasemovesdowntheDNAchaincausingtemporaryopeningofthedoublehelix.延长阶段StepsinRNAsynthesis3:WhenWhenaterminationsiteisreached,andthemRNAandpolymeraseareShanghaiJiaoShanghaiJiaoTongTheTheysakeyroleintheinitiationofRNAThesigmafactor,aspartoftheRNApolymerase,isinvolvedWheredoesthesentencebegin?Twosequenceswithinthepromoterregionarehighlyconserved,itisOneisabout10basesfromthestartoftranscription:–10region Thesecondis35sequence–35FLASHFLASH.3Wheredoesthesentenceend? InBacteriaacommonterminatorisasequencecontaininganinvertedrepeatwithacentralnonrepeatingsegmentfollowedbyrunsofuridines.细菌中常见的终止子是反向重复序列ShanghaiJiaoTongFLASHFLASHInvertedInvertedrepeatsintranscribedDNAleadtoformationofastem-loopstructureintheRNA InE.coli,RhoproteinbindstightlytoRNAandmovesthechaintowardRNApolymerase-DNAcomplex.OnceRNApolymerasepauseataRho-dependentterminationsite,Rhocanpausethetermination.ShanghaiJiaoTong7.7.4RNAProcessing Removalofanintronfromthetranscriptineukaryote.Thepre-mRNAwithasingleintron.ThesequenceGUisconservedat5’splicesiteandAGat3’splicesite.SeveralsmallribonucleoproteinparticlesassembleontheRNAtoformaspliceosome.The5’splicesitehasbeencutwiththesimultaneousformationofabranchpoint.ShanghaiJiaoTongTheThe3’splicesitehasbeencut,whilethetwoexonswerejoined.Thefinalproductsarethejoinedexons,themRNAandthereleasedintron(lariat套索).ShanghaiJiaoTongMature

Overviewofofthepre-mRNAintomRNAin(c)TheintronissplicedAribosomalRNAprecursorcontainsan(b)Followingtheadditionoftheintronsplicesitselfoutandthetwo

(d)Theintroncircularizeswiththelossofa15-nucleotideSelf-splicingribozymalintronofprotozoanTetrahymenaThereisconsiderablesecondarystructureinsuchmoleculeswhichiscriticalforthesplicingreaction.四膜虫的核酶内含子的自剪切V.PROTEINTheGenetic7.9.Transfer7.10Translation:theprocessofproteinShanghaiJiaoTongShanghaiShanghaiJiaoTongThegeneticThreebasesdetermineoneaminoacid43=643stopcodons,UAA,UAG,UGA1startcodon,AUGforN-formylmethionine61sensecodonsfor20aminoacids(degenerate简ShanghaiJiaoTongShanghaiJiaoTongShanghaiJiaoTongThegeneticcodonsarehighlydegeneratebasepairingismoreflexibleforthethirdbaseofthecodon.简并性PossiblePossiblereadingframesinanmRNATransferStructureofatRNAcloverleaffashiontRNA具有SecondarystructureconservativeregionsthetCloopandDloops)orregionswithspecificfunctions(anticodonloopandacceptorend).二级ShanghaiJiaoTongStructureofaTranslation:theprocessofproteinShanghaiJiaoTongtRNAtRNAcarriesaminoacidtothegrowingpeptidechainsequencedeterminedby(i,ii)In ctionbetweenthecodonandanticodonbringsintothepositionthecorrectchargedA-acceptorsite,P-site,andE-exitinitiator(iii(iiiElongationapeptidebondformedbetweenaminoacidsonadjacenttRNAmolecules.肽键形成ShanghaiJiaoTong(iv(ivTranslocationoftheribosomefromonecodontothenextwiththereleaseofthetRNAfromtheE-site.移位与ShanghaiJiaoTong(v)(v)ThenextchargedtRNAbindstotheA-FLASH4anghaiJiaogi5Polysome:SeveralribosomestranslateasinglemRNAmoleculesimultaneously.多核糖体ShanghaiJiaoTongFoldingandSecretingTofunctioncorrectly,proteinsmustbeproperlyFoldingmayoccurspontaneouslybutmayalsoinvolveotherproteinscalledmolecularchaperones.分ShanghaiJiaoTongEnergyforrefoldingcomesfromATPFourkeychaperonesinE.coliareDnaK,DnaJ,GroELManyproteinsalsomustbetransportedintoorthroughcellmembranes.Suchproteinsaresynthesizedwithasigna