In the lac operon, maximal transcription occurs under which combination of conditions?
- A High glucose, high lactose
- B High glucose, low lactose
- C Low glucose, high lactose ✓
- D Low glucose, low lactose
Correct answer: C. Low glucose, high lactose
Explanation
With high lactose, allolactose binds the lac repressor and relieves its block at the operator. With low glucose, adenylyl cyclase activity rises, intracellular cAMP increases, and the cAMP-CRP (CAP) complex binds upstream of the promoter to recruit RNA polymerase strongly. Only low glucose plus high lactose satisfies both requirements, giving positive activation together with relief of negative repression. High glucose causes catabolite repression regardless of lactose availability.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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