OPERONS-REPRESSIBLE AND...
Transcript of OPERONS-REPRESSIBLE AND...
OPERONS-REPRESSIBLEANDINDUCEIBLE
AnoperonisaregioninprokaryoticDNAthatcodesforseveralgenesatthesametime.Theoperoniscomposedofapromoterregionthatcontainstheoperatorandseveralgeneslinedupnexttoeachother.Eachgenehasastartandstopcodon,butsincetheyaresoclose,theenzymesformoneafteranother.ThemRNAwillbetranscribediftheRNAPolymerasecangetpasttheoperator.Ifthereisarepressorproteinintheoperatorthantheenzymesarenotsynthesized.IftherepressorproteinisNOTintheoperator,thenthemRNAwillbetranscribed.Therepressorproteiniscodedupstreamfromtheoperon,soitisthereifitneedstobe.
Intheaboveexample,willtheRNAPolymerasetranscribethegenes?Explain.Intheaboveexample,willRNAPolymerasetranscribethegenes?Explain.
GeneforRNAOperatorGenesRepressorPolymeraseProtein(Upstream)
AnoperonisaregioninprokaryoticDNAthatcodesforseveralgenesatthesametime.Theoperoniscomposedofapromoterregionthatcontainstheoperatorandseveralgeneslinedupnexttoeachother.Eachgenehasastartandstopcodon,butsincetheyaresoclose,theenzymesformoneafteranother.ThemRNAwillbetranscribediftheRNAPolymerasecangetpasttheoperator.Ifthereisarepressorproteinintheoperatorthantheenzymesarenotsynthesized.Therepressorproteinistranscribedupstreamfromtheoperon,soitisthereifitneedstobe.
Wewilllearnabout2operonsbutthereareseveralotherswewillnottalkabout.
AnoperonisaregioninprokaryoticDNAthatcodesforseveralgenesatthesametime.Theoperoniscomposedofapromoterregionthatcontainstheoperatorandseveralgeneslinedupnexttoeachother.Eachgenehasastartandstopcodon,butsincetheyaresoclose,theenzymesformoneafteranother.ThemRNAwillbetranscribediftheRNAPolymerasecangetpasttheoperator.Ifthereisarepressorproteinintheoperatorthantheenzymesarenotsynthesized.Therepressorproteinistranscribedupstreamfromtheoperon,soitisthereifitneedstobe.
Wewilllearnabout2operonsbutthereareseveralotherswewillnottalkabout.
RepressorProtein
Wewilllearnabout2operonsbutthereareseveralotherswewillnottalkabout.ThefirstiscalledtheTRPOperon-REPRESSIBLE.Prokaryotesneedtheaminoacidtryptophan(Trp)inordertobuildproteinsandenzymes.IftheTrpisobtainable,theprokaryoteswilluptakeitandbuildallofthenecessaryproteinsandenzymes.IfTrpisnotpresent,theprokaryotesneedtosynthesizeitthemselves.Theycanachievethisthroughaseriesofenzymaticreactions.RNAPolymerasewillbindtothepromoterregionandtranscribethemRNAneededforthenecessaryenzymes.TheywillcontinuetosynthesizetheTrpuntiltheyhaveenough.Oncethatamountisreached,allofthegenesthatcodefortheenzymesareturnedofftogether.ThishappenswhenTrpbindsallostericallytotherepressorproteinandaltertheactivesite.TherepressorproteinwillnowfitintheoperatorblockingtheRNAPolymerasefromtranscribingmRNA.Thisiscalled“REPRESSINGTHEGENES”IfthereisnoTrpinthecell,therepressorproteinisproducedbutWILLNOTFITintheoperatorsite.TheRNAPolymerasewillmovedownandtranscribemRNAthatwillcodeforthe5enzymesneededtosynthesizemoreTrp.IfTrpispresent,itwillallostericallybindtotherepressorproteinandchangeitsshape.TherepressorproteinwillNOWFITINTOtheoperatorandblocktheRNAPolymerase.
ThesecondiscalledtheLacOperon-INDUCEIBLELactoseisadisaccharidecomposedofglucoseandgalactose.ProkayoteslikeEcoliliveinourgutandareexposedtolactosewhenweeatthingslikecheese.Thesebacterianeedglucose.Inordertogettheglucosefromthelactose,theyneedaseriesofenzymesthatcanbreakdownthelactose.Interestingly,theEcoliwillonlyproducetheseenzymeswhenlactose,oritsisomerallolactosearepresent.Veryeconomical.IfthereisNOTlactoseorallolactosearound,arepressorproteinisintheoperatorsiteblockingtheRNAPolymerasefrommakingenzymesneededtobreakdownlactose.Ifallolactoseisaround,itwillallostericallybindtotherepressorproteinandchangetheactivesite.ItwillNOLONGERFITintotheoperatorregion.Iftherepressorproteinisnotthere,theRNAPolymerasecantranscribetheenzymesneededtobreakdowntheallolactoseintotheglucoseitneeds.Thisiscalled“INDUCINGTHEGENES”
AnoperonisaregioninprokaryoticDNAthatcodesforseveralgenesatthesametime.Theoperoniscomposedofapromoterregionthatcontainstheoperatorandseveralgeneslinedupnexttoeachother.Eachgenehasastartandstopcodon,butsincetheyaresoclose,theenzymesformoneafteranother.ThemRNAwillbetranscribediftheRNAPolymerasecangetpasttheoperator.Ifthereisarepressorproteinintheoperatorthantheenzymesarenotsynthesized.Therepressorproteinistranscribedupstreamfromtheoperon,soitisthereifitneedstobe.
Wewilllearnabout2operonsbutthereareseveralotherswewillnottalkabout.
RepressorProtein
Allolactosebindsandalterstherepressorprotein.Itcannolongerbondtotheoperatorsite.
RNAPolymerasecantranscribethemRNAthatwillgoontocreatetheenzymesneededtodigestthelactose.
TryptophanSynthesisRepressible
LactoseDigestionInducible