POSITIVE AND NEGATIVE CONTROL IN LAC OPERON: Positive control: - lactose binding to LacI (repressor), preventing it from binding to the operator, and therefore allowing RNA polymerase to bind to the promotor. - Absense of glucose allows cAMP to be formed, which binds to CRP. cAMP-CRP binds to the activator binding site which promotes RNA polymerase to bind to the promotor Negative control: - In the absense of lactose, LacI (repressor) binds to the operator and prevents RNA polymerase from binding to the promotor, therefore no transcription - Presence of glucose inhibits the enzyme adenylate cyclase which is involved in the formation of cAMP. Without cAMP-CRP, it does not bind to the activator binding site
Posted on: Sat, 08 Jun 2013 09:25:15 +0000
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