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SchoolofLifeScienceandTechnologyShanghaiJiaoTongUniversitySchoolofLifeScienceandTechnologyShanghaiJiaoTongUniversityLecture7-PrinciplesofMicrobialMolecularBiologyAtinymaninthespermAtinymaninthespermTheoldestquestions:whyandhowcanparentstransferthebasictraitstotheirchildren?Dotheydirectlymakeacopyofthemselvesandusethattoproducetheirbabies?Ifbabiesdevelopfromthecombination(fertilization)ofeggandspermcells,whatarereallyinsidethesecellstomakethembecomethebaby?I.GenesandGene7.1MacromoleculesGeneticI.GenesandGene7.1MacromoleculesGeneticAgeneisaAgeneisaDNAsegmentspecifyingthesequenceofaprotein(orarRNA,tRNA)Proteinsynthesis:informationwithinDNAmoleculeisusedtodirectthelinkingofdifferentaminoacidsinaspecificorder/GenesandCentralaCentralThreeCentralaCentralThreeReplicationTranscriptionTranslationFig.7.1StepsinInformationReplication,transcription,andtranslationoccurinallorganisms.Replication,transcription,andtranslationoccurinallorganisms.Therearesomedifferencesinprokaryotesandineukaryotes.ProkaryoticandEukaryoticInformationtransferinprokaryotesInformationtransferinprokaryotesAsinglemRNAoftencontainsmorethanonecodingregion(polycistronic)多顺反子的Figure:07-Noncodingregions(introns)areremovedfromtheprimarymRNAbeforetranslation.ThemRNAsofeukaryotesarealmostNoncodingregions(introns)areremovedfromtheprimarymRNAbeforetranslation.ThemRNAsofeukaryotesarealmostinformationtransferineukaryotes真核生HowdoesHowdoesthebasesequenceinDNAdetermineaminoacidsequenceinprotein?RosettastoneanddecodingofRosettastone:ThesamemessagewasinscribedinthreedifferentlanguagesHieroglyphs,demoticandGreek罗塞塔石:ThesamegeneticinformationwasencodedinthreeformsDNAbasemRNAbaseAminoacidII.DNA7.2II.DNA7.2DNAStructure:TheDoubleHelix双螺旋DoublehelixmodelofDNAandthetwoyoungdiscoversDoublehelixmodelofDNAandthetwoyoungdiscoversCrick,35yearoldPhDstudentoldpostThebasicunitofDNAThebasicunitofDNAmolecule:RibonucleotidefoundinStructuralfeaturesofDNAonechainendsStructuralfeaturesofDNAonechainendsina5’-phosphategroup,whereastheotherendsina3’-5’p-AGTCGTCATTAGCT-OHDNAstrandhasTwocomplementaryA-T,G-CTwocomplementaryA-T,G-CcouplingviahydrogenInanti-paralleldirections-headtoOnestrandisindirectionof5’P-Theotherstrandisindirectionof3’OH-DNAasadoubleDoublehelixDoublehelixmodelofFiguresitesforGCpair:3GCpair:3hydrogenATpair:2hydrogenOnenucleotidemolecularweight:Onenucleotidemolecularweight:1kb=kilobasepairs(onethousand1Mb=magabasepairs(onemillionEachbasepairtakes0.34nmalongtheEachturntakes10basepairs,3.4nm1kb=100turns=0.34E.coligenome=4.6ImportantFigure7- InvertedrepeatFigure7- Invertedrepeat:sequencesthatrepeatininverseorientation.Nearbyinvertedrepeatscouldtheoreticallyleadtotheformationofstem-loop(cruciformstructuresinSequence-specificFeatureofHairpinlikeaHairpinlikeastem-loopbutwithalmostnoloop发夹Hairpinsisusuallyformedfromasingle-strandedregionattheendofamoleculethatcontainsaninvertedrepeat.5.3DNAStructure:5.3DNAStructure:LamdaLamda48.6LamdaLamda48.6kb,17E.4,000kb,1.5613,500kb,4.6165,000kb,562,900,000kb,990DNAmoleculesareveryGenomesizesGenomesizesvarygreatlyrangingfromviruseswiththesmallesttoalgaeandvertebratespossessingthegreatestamount.DNA:1mmCell:2-3mBacterialNucleoidHowcanaHowcanaverylongmoleculebepackagedinaBygentlylysingBygentlylysingthecells,thehighlycompactednucleoidofthecellswillemergeintact.SupercoilingistheSupercoilingisthefurtherSupercoilingisthefurthertwistingofDNAdoublehelix----coilingofcoilsDirectionsofNegative-DNAistwistedaboutitsaxisintheoppositedirectionfromthatoftheright-handeddoublehelix.(predominantlyfoundinnature)DNAsupercoiling超螺ThelinearDNAiswoundaroundproteinscalledhistonestoformnucleasomesThelinearDNAiswoundaroundproteinscalledhistonestoformnucleasomesDNA围绕NucleosomenegativesupercoilsNucleosomeintroducenegativesupercoilsineukaryotes核小体TopoisomeraseII(DNAgyrase)-breakandresealofdoublestrands拓扑异TopoisomeraseII(DNAgyrase)-breakandresealofdoublestrands拓扑异构酶II(DNA促TopoisomeraseI-breaksinglestrand,removesupercoilinginDNA拓扑异构酶I(DNA解旋SupercoilingisintroducedbyDNAgyraseinBacteriaandmostArchaeaIntroductionofsupercoilingintoIntroductionofsupercoilingintoacircularDNAbyactivityoftopoisomeraseII,whichmakesdouble-strandbreaks.Figure