prokaryotic gene regulation：原核基因表达调控

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1、AnticipatoryQuestions1.Whatmighthappenifanorganismhaditscellsexpressingallgeneswithinthegenomeallthetime?2.Atwhatlevelscancontrolofcellularactivities/pathwaysbecontrolled?3.Basedonourdiscussionsuptothispoint,whatdoyouthinktheterm“negativefeedback”means?4.Whatstepsareinvolvedintheinitiationofp

2、rokaryotictranscription?LearningObjectivesunderstandthatregulationofgeneexpressionisameansbywhichtocontroltimingandrateofgenerationregardingfunctionalgeneproduct(eitherRNAorpolypeptide/protein).explaintheconceptofanoperonintermsofcomponents’functions(promoter,operator,repressor,co-repressor,i

3、nducer,genecluster,polycistronictranscript).compareandcontrastrepressibleandinducibleoperonsystems/pathways.compareandcontrastnegativeversuspositiveregulationofoperonsapplytheoperonconcepttogeneexpressionasitrelatestogeneticengineering(specifically,ourcloningandexpressionofthe“tomato”gene).In

4、dividualbacteriarespondtoenvironmentalchangebyregulatingtheirgeneexpressionAbacteriumcantuneitsmetabolismtothechangingenvironmentandfoodsourcesThismetaboliccontroloccursontwolevels:AdjustingactivityofmetabolicenzymesRegulatinggenesthatencodemetabolicenzymesLE18-20RegulationofenzymeactivityReg

5、ulationofenzymeproductionEnzyme1RegulationofgeneexpressionEnzyme2Enzyme3Enzyme4Enzyme5Gene2Gene1Gene3Gene4Gene5TryptophanPrecursorFeedbackinhibitionOperons:TheBasicConceptInbacteria,genesareoftenclusteredintooperons,composedofAnoperator,an“on-off”switchApromoterGenesformetabolicenzymesAnopero

6、ncanbeswitchedoffbyaproteincalledarepressorAcorepressorisasmallmoleculethatcooperateswitharepressortoswitchanoperonoffLE18-21aPromoterPromoterDNAtrpRRegulatorygeneRNApolymerasemRNA3¢5¢ProteinInactiverepressorTryptophanabsent,repressorinactive,operononPolycistronic*mRNAtrpEtrpDtrpCtrpBtrpAOper

7、atorStartcodonStopcodontrpoperonGenesofoperonEPolypeptidesthatmakeupenzymesfortryptophansynthesisDCBA5¢*=mRNAcarriestheinformationofseveralgenes,whicharetranslatedintoseveralproteinsLE18-21b_1DNAProteinTryptophan(corepressor)Tryptophanpresent