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Lecture 20

Lecture 20 - Operon - BIOL308.pdf

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BIOL 308
Bruce Wolff

Lecture 20Basic ReviewLactose operonCatabolic negative regulationRegulatory protein is repressor effectorinducer allolactoseExistence of catabolic activator protein CAPTryptophan operonAnabolic negative regulationRegulatory protein is aporepressoreffectorcorepressor tryptophanAutoregulationLarabinose operonCatabolic positive AND negative regulationSame regulatory protein acts as both activator and repressorregulator two different conformationscorresponding binding sitesEffectorinducer arabinoseAutoregulaton of AraC and CAP regulation of the operonRegulation of transcription in prokaryotes contMultiple operators auxiliary operatorsOperator regions more complicated then previously shownLacoperon region contains 3 operatorsStrongest commonly shown O1DownstreamO2Inside lacZ reading frameUpstream O3All three present transcription suppressed 1000foldIf either O2 or O3 are missing 500foldBoth O2 and O3 missing 20foldRepressor binds as a tetramercould bind to all three of themDNA loopingRNAP prevented from binding to promoterAlsopresence of auxiliary operators O2 and O3 near the functional operator O1 increase the local concentration of the repressor so that it can occupy the functional operator O1Regulation of transcription in Prokaryotes conttwo component regulatory systemOne protein is the sensortransmitter protein1Monitors specific changes in the environment level or nutrients pH solvent ceoncentrationosmolarity etc KinaseSecond protein is response regulator protein2Either stimulates or represses regulation of specific genesChanges in gene expression necessary for bacterium to adapt to environmental changeTwo compoenent regulatory system contSensortransmitterusually spans across the cell membraneSensoris an outer part which detects specific changes in environment transmitteris an inner part which usually acts as a kinaseChanges in the environment sensed by sensorChange of the conformation of sensor domainChange of the conformation of sensor domain activities change of conformationtransmitters kinase partin the cellActivated kinaseAutophosphorylationof the transmitter domain transfer usually gamma phosphate from the ATP to itselfChange of conformationThe same phosphate is then transferred to the receiver domainof response regulator change of conformation activation of the effector domainResponse regulator binds to DNA regulatory sequences in genes encoding proteins that help cell to cope with environmental change NOTES FROM LECTURES Page 1
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