Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyeasymcq1 pt

Escherichia coli is moved into medium containing lactose as the only sugar. How do lac operon transcripts change, and why?

A.Transcription stops because lactose acts as a corepressor that locks the repressor onto the operator
B.Nothing changes, because bacterial promoters respond only to temperature and pH
C.Transcription rises because bound allolactose detaches the repressor, letting RNA polymerase reach the promoter
D.The operon is deleted after lactose is consumed, ending enzyme production permanently

Explanation

Core Concept

Cells convert some imported lactose into allolactose, which binds the lac repressor and changes its shape. The reshaped repressor releases the operator, clearing the path for RNA polymerase. With glucose absent, cAMP is high, so the catabolite activator protein further boosts promoter binding.

Correct Answer

CTranscription rises because bound allolactose detaches the repressor, letting RNA polymerase reach the promoter

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