Bio326RSu19.08.BacterialGeneRegulation.pptx

Repressor gene repressor active repressor inducer

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Repressor gene, repressor, active repressor, inducer, inactive repressor Positive control, cAMP, Catabolite Activator Protein TRYPTOPHAN OPERON (anabolic) Structural genes Control sites (promoter, operator, attenuation site) Repressor - inactive - co-repressor, active repressor Attenuation coupled transcription and translation fine tuner of gene expression leader peptide, trp codons alternative structures of mRNA, molecular switch
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CATABOLIC OPERON - LACTOSE LACTOSE LACTOSE b - GALACTOSIDASE GLUCOSE AND GALACTOSE PROTEINS NEEDED: LACTOSE TRANSPORT b - GALACTOSIDASE LACTOSE GENES OFF GLUCOSE PROTEINS NEEDED: FOR GROWTH LACTOSE TRANSPORT b - GALACTOSIDASE LACTOSE GENES ON
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Promoter b -galactosidase Operators b -gal. Permease b -gal. Transacetylase Lac Operon
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LACTOSE OPERON IS SUBJECT TO POSITIVE CONTROL GROW IN LIMITING CONCENTRATIONS OF GLUCOSE AND LACTOSE TIME LOG TURBIDITY b - GALACTOSIDASE LEVEL CELLS USE GLUCOSE FIRST NO b - GALACTOSIDASE IN PRESENCE OF GLUCOSE GLUCOSE PREVENTS POSITIVE CONTROL FROM ACTIVATING GLUCOSE INHIBITS cAMP SYNTHESIS cAMP = CYCLIC ADENOSINE MONOPHOSPHATE - NEEDED TO ACTIVATE CAP CAP = CATABOLITE ACTIVATOR PROTEIN
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- Lactose lac Repressor No Transcription + Lactose Transcription Lactose Negative Control
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+ Lactose Transcription + Lactose Transcription Lactose Positive Control RNAP RNAP
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Cyclic AMP “Second messenger” Generated by adenylate cyclase Presence of lactose
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cAMP BINDS CAP; ACTIVATES CAP cAMP-CAP BIND CAP SITE TO STIMULATE TRANSCRIPTION POSITIVE CONTROL OF LAC ATP + PPi CYCLIC AMP GLUCOSE INHIBITS ADENYLATE CYCLASE
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Cyclic AMP Bound by catabolite activator protein (CAP) Active for DNA binding Activated CAP/cAMP binds to DNA elements in promoter (cyclic AMP resposive elements = CREs) Increase in transcription rate How?
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GROWTH MEDIUM NEGATIVE CONTROL REPRESSOR-OPERATOR POSITIVE CONTROL cAMP-CAP ACTIVATOR RESULT GLUCOSE (ONLY) LAC REPRESSOR IS SYNTHESIZED; IS ACTIVE; BINDS OPERATOR; INHIBITS RNA POLYMERASE GLUCOSE INHIBITS ADENYLATE CYCLASE; NO cAMP SYNTHESIS; cAMP-CAP CANNOT BIND ACTIVATOR SITE LAC IS OFF LACTOSE (ONLY) LAC REPRESSOR IS SYNTHESIZED; IS INACTIVATED BY LACTOSE; (ALLO-LACTOSE); CANNOT REPRESS cAMP IS SYNTHESIZED; cAMP AND CAP BIND ACTIVATOR SITE; STIMULATE RNA POLY- MERASE TO TRANSCRIBE LAC IS ON GLUCOSE AND LACTOSE LAC REPRESSOR IS SYNTHESIZED; IS INACTIVATED BY LACTOSE; (ALLO-LACTOSE); CANNOT REPRESS GLUCOSE INHIBITS ADENYLATE CYCLASE; NO cAMP SYNTHESIS; cAMP-CAP CANNOT BIND ACTIVATOR SITE LAC IS OFF (UNTIL ALL THE GLUCOSE IS USED) FOR CELLS GROWING IN THE FOLLOWING CONDITIONS, THE LAC OPERON WILL BE CONTROLLED IN THE FOLLOWING WAYS: 8-2
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Learning Objectives 8.2 Know the different mechanisms used to
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  • Fall '05
  • GlennEllison
  • DNA

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