When Does Repression of the Lac Operon Occur

Question

When does repression of the lac operon occur?
A)When allolactose binds to the operator region.
B)When allolactose binds to the repressor protein.
C)When the repressor protein binds to the operator region.
D)When allolactose binds to β-galactosidase.
E)When the repressor protein binds to the promoter.

Accepted Answer

Repression of the lac operon occurs when the repressor protein binds to the operator region. This prevents RNA polymerase from binding to the promoter and transcribing the genes involved in lactose metabolism. Allolactose functions as an inducer of the lac operon by binding to the repressor protein and causing it to release from the operator. Therefore, choices A and B are incorrect. Allolactose does not bind to β-galactosidase or affect its activity, so choice D is incorrect. The repressor protein does not bind to the promoter but rather the operator, so choice E is also incorrect.