Q13 - lac Operon Regulation (Glucose and Lactose)
Theory
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Q13. An E. coli culture was grown under four nutrient conditions and beta-galactosidase activity measured. Which statement most accurately explains the molecular basis for the observed results?
a The presence of glucose prevents formation of CAP-cAMP complex limiting operon induction even when lactose is available. b Absence of glucose permits efficient uptake of lactose, but allolactose cannot inactivate the repressor unless cAMP is degraded, hence transcription remains low. c When both lactose and glucose are absent, the lac operon is repressed solely because CAP-cAMP complex binds strongly to the promoter, preventing RNA polymerase attachment. d Glucose enhances adenylate cyclase activity, producing high cAMP that represses lac operon transcription until lactose concentration falls below threshold.
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