Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyhardmcq1 pt

Which combination of conditions drives maximal transcription of the Escherichia coli lac operon, and through which regulatory events?

A.Lactose present with glucose scarce: allolactose frees the operator while high cAMP loads the activator protein that assists polymerase binding
B.Glucose abundant with lactose absent: low cAMP activates CAP while the repressor guards the operator
C.Lactose present with glucose abundant: the repressor departs but weak promoter binding limits transcription
D.Both sugars present: lactose destroys cAMP so CAP clamps tightly onto the promoter

Explanation

Core Concept

Inducer-bound LacI cannot occupy the operator, so repression lifts. Scarcity of glucose raises cyclic AMP, and the cAMP-CAP complex attaches upstream of the lac promoter. This complex improves RNA polymerase recruitment, so negative and positive controls act together to maximize output.

Correct Answer

ALactose present with glucose scarce: allolactose frees the operator while high cAMP loads the activator protein that assists polymerase binding

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