The expression of the tryptophan operon is controlled by a(n)
A) repressor that is active when it is alone.
B) repressor that is inactive when it binds to lactose.
C) repressor that is active when it binds to tryptophan.
D) activator that turns the operon on by binding to DNA.

Question

Quizplus · Accepted Answer

The expression of the tryptophan operon is controlled by a repressor that is active when it binds to tryptophan. When tryptophan levels are high, the repressor becomes active and binds to the operator region of the operon, preventing RNA polymerase from transcribing the genes for tryptophan biosynthesis. When tryptophan levels are low, the repressor is inactive and cannot bind to the operator, allowing transcription to occur.

The Expression of the Tryptophan Operon Is Controlled by A(n)