Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologymediummcq1 pt

Tryptophan becomes plentiful in the environment of an E. coli culture. Describe the regulatory response of the trp operon.

A.Tryptophan binds RNA polymerase and directs it to transcribe the biosynthetic genes faster
B.Low tryptophan switches the repressor on, mirroring inducer logic used by the lac system
C.Tryptophan binds the repressor as a corepressor, enabling it to occupy the operator and shut transcription down
D.Tryptophan enters the operator directly and physically obstructs transcription initiation

Explanation

Core Concept

The inactive repressor alone cannot grip operator DNA. Binding tryptophan completes its DNA-reading surface, so the complex parks on the operator and repels polymerase. Because the end product suppresses its own synthesis pathway, the operon is classified as repressible.

Correct Answer

CTryptophan binds the repressor as a corepressor, enabling it to occupy the operator and shut transcription down

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