4 Gene Regulation and Lac Operon notes

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1、GENEREGULATION•PURPOSE:–Importantforcellularcontrolanddifferentiation.•Cellswillonlymakeproteinsthattheyneedwhentheyneedthem.–Cellsthatarespecializedtoperformaspecificfunctionwillhavespecificgenesturnedonthatothercellswillnot(Redbloodcell–hemoglobinison,inaneuronthisisnoton)–Cellswil

2、lonlymakeproteinsthattheyneedwhentheyneedthem(theywasteenergymakingproteinstheydonotneedEX:LacOperoninprokaryotes)OperonModel•Aseriesofgenesthatcodeforspecificproductsandtheregulatoryelementsthatcontrolthesegenes•JacobandMonod(1961)-Prokaryoticmodelofgenecontrol.OperonStructure(impor

3、tantthingstoknow)1.RegulatoryGene–MakesarepressorproteinthatcanbindtotheDNAandblocktranscription2.OperonAreaa.Promoter–sitewheretheRNApolymeraseattachestotheDNAb.Operator–sitetherepressorproteincanbindc.StructuralGenes–thesegmentthatcodesforthemRNAthatwillbecomeaproteinGeneStructures

4、LacOperon•FordigestingLactose.•InducibleOperon-onlyworks(on)whenthesubstrate(lactose)ispresent.IfnoLactose•Repressorbindstooperator.•Operonis"off”(thereisaroadblock),notranscription,noenzymesmadeIfLactoseisabsentIfLactoseispresent•RepressorbindstoLactoseinsteadofoperator.•Operonis"on

5、”(thereisnoroadblock),transcriptionoccurs,enzymesaremade.IfLactoseispresentEnzymes•DigestLactose.•WhenenoughLactoseisdigested,theRepressorcanbindtotheoperatorandswitchtheOperon"off”.Net(overall)Result•ThecellonlymakestheLactosedigestiveenzymeswhenthesubstrateispresent,savingtimeanden

6、ergy.Fig.18-4RegulatoryPromotergeneOperatorDNAlacIlacZNoRNAmade3′mRNARNA5′polymeraseActiveProteinrepressor(a)Lactoseabsent,repressoractive,operonofflacoperonDNAlacIlacZlacYlacARNApolymerase3′mRNAmRNA5′5′Proteinβ-GalactosidasePermeaseTransacetylaseAllolactoseInactive(inducer)repressor

7、(b)Lactosepresent,repressorinactive,operononANIMATION•See5minutevideo☺