交大微生物课件lecture10-1bacterial genetics

HowcanwechangeinformationencodedinaLectureLecture10-1BacterialI.Mutation Chapter10BROCKBIOLOGYOFSchoolofLifeScienceandTechnology,ShanghaiJiaoTongUniversity ShanghaiJiaoTongMutationsandImportantAheritablechangeinthebasesequenceofthegenomeofanAstraincarryingsuchaheritableAstrainisolatedfrom AprecisedescriptionofthegenesanorganismTheobservablepropertiesofanShanghaiJiaoTongDesignationsinmicrobialgeneticsGenotypeThreelowercaselettersfollowedbyacapitalletter(allinGene’sproductAcapitalletterfollowedbytwolowercaselettersandthenacapitalletterHisC,PhenotypeAcapitalletterfollowedbytwolowercaseletters,witheitheraplusorminussuperscripttoindicatethepresenceorabsenceofthatpropertyHis+,ShanghaiJiaoTongIsolationofmutantsScreeningVersusSelection突变Nonselectablemutants-pigmentmutation非选择性变异mutantswithnoadvantageordisadvantageoverparentalcellswhengrowingunderartificialconditions.TheonlywaytofindanonselectablemutantistoscreenalargepopulationofthebacteriumSelectablemutants-drug mutantswithanadvantageundercertainenvironmentalconditions,sotheprogenyofthemutantcellareabletooutgrowandre cetheparentcells.ShanghaiJiaoTongPigmentedmutantsandnonpigmentedmutantsofAspergillus.Thewildtypehasagreenpigment.Thewhitemutantsmakenopigment,whereastheyellowmutantscannotconvertthepigmenttothenormalShanghaiJiaoTongFig.10.1Fig.10.1Antibiotic-resistantmutantswithintheinhibitionzoneofanantibioticassaydisc.抗生素抗性突变株ShanghaiJiaoTongScreeningistoobserveallthecellsinapopulationtoidentifymutantsfromparentcells筛选：从群体中观察Selectionistogrowpopulationundercertainconditionssothatmutantswillgrowfasterthanparentcells(eventually ethemajorityoreventheonlycelltypesinthepopulation).选择：在特定培养条件中使变异株成ShanghaiJiaoTongPositiveselectionfor -mutantswhichareresistanttosomeantibioticcanbeselectedbygrowingonmediumcontainingthisdrug药物NegativeselectionwhichisnotforthemutantbutagainstparentaltypePenicillinonlykillactivelygrowingIsolationofNutritionalAuxotrophsandPenicillinSelection营养缺乏型的ShanghaiJiaoTongAnutritionalmutantthathasarequirementforagrowthThewildtypeparentforanutritionalShanghaiJiaoTong tingmethod-apowerfultoolforscreening平板 Imprintofcoloniesfromamaster teismadeonto tefortestingnutritionalmutantComparisonofgrowthofcoloniesonmasterand teswillidentifythemutantsFig10-Usingsterilevelveteenclothorfilterpaper,animprintofcoloniesfromamaster teismadeontoanagar telackingthenutrient.Thecoloniesoftheparentaltypewillgrownormally,whereasthoseofthemutantwillnot.Thus,theinabilityofacolonytogrowonthereplica teisasignalthatitisamutant.ShanghaiJiaoTong ting

Complete MinimalFig.10.2Thereplica telackedonenutrientpresentinthe te.Therefore,thecoloniesmarkedwithanXareShanghaiJiaoTongPrinciple1NutritionalAuxotrophsareatadisadvantageincompetitionwiththeparentcellsandsonodirectwayofisolating.营养Principle2:Penicillinkillsonlygrowingcells,andifpenicillinaddedtoamediumlackingthegrowthfactor,theparentcellswillbekilledwhereasthenongrowingmutantcellswillbeunaffected青霉素Afterpreliminaryincubation,thepopulationiswashed ofpenicillinandtransferredto tescontainingthegrowthfactor经过预备培养，ShanghaiJiaoTong10.2MolecularbasisofChangeofbasesequenceinthegeneticmaterialisthemolecularbasisforallmutations遗传物质碱基序列ChangeofoneoraveryfewbaseInsertionsanddeletionsChangeofmanybasepairs,hundredsoreventhousandsofbasepairscanberemovedoraddedtothegenomeFigure:Figure:10- ShanghaiJiaoTong10.2.2FrameshiftmutationFigure:10-ShanghaiJiaoTongShanghaiJiaoTong10.4MutagenesisandChemicalmutagensBiologicalmutagens生物诱变物质ShanghaiShanghaiJiaoTongShanghaiShanghaiJiaoTongShanghaiJiaoTongFigure:10-PyrimidineShanghaiJiaoTongMutationsthatarisefromDNArepair:TheSOSSystemCellshaveavarietyofdifferentDNArepairprocessestocorrectmistakesorrepairdamage.Someprocessesseemtobeerror-SOSregulatorysystem:someDNArepairoccursintheabsenceof teinstruction(withoutbase-pairing),whichresultsinthecreationofmanyerrors一些DNA修复过程是在没有模板的指SOSFig.10.7TheSOSsystemisnormallyrepressedbyaproteincalledLexA.However,thisrepressorproteinisinactivatedbyRecA,aproteasethatisactivatedasaresultofDNAdamage.SOSLexAproteinrepressestheactivitiesoftherecAgeneandtheDNArepairgenesuvrAandumuD.(therepressionisnotcomplete.SomeRecAproteinisproducedeveninthepresenceofLexAprotein).WithLexAinactivatedbyRecA,thesegenes eactive.ShanghaiJiaoTong10.5MutagenesisandCarcinogenesis:TheAmes SafetytestforChemicalswhichcancausecellmutationarepotentialagentsforinducingcancersinhumanbeings可造成细胞突变的化学物Principle:Mutationrateofbacterialpopulationisagoodestimateformutagenicityofchemicals细菌菌群的突变ShanghaiJiaoTongProtocolforanAmesDetectionofbackmutationinauxotrophicmutants-Increaseoftherateofbackmutationisanindicationofmutagenicityofthetestedchemical回复突变增加表Fig.10.8Both teswereinoculatedwithacultureofahistidine-requiringmutant.Themediumdoesnotcontainhistidine,soonlycellsthatrevertbacktowildtypecangrow.Spontaneousrevertantsappearonboth tes,butthechemicalhascausedanincreaseinthemutationrate.ShanghaiJiaoTongShanghaiJiaoTongItdoesnotnecessarilyfollowthatbecauseacompoundismutagenicitisalsocarcinogenic.Thecorrelation,however,isvery Thefactthatacompoundisnotmutagenicinabacterialsystemdoesnotmeanthatitisnotcarcinogenic,在细菌实验系统中无 Why:bacterialsystemcannotdetectallcompoundsacti