In negative control of transcription by the lac operon, how does the presence of an inducer affect transcription?
A) The inducer binds to the operator.
B) The inducer does not bind to the operator.
C) The inducer causes the repressor to bind to the operator.
D) The inducer prevents the repressor from binding to the operator.

Question

Quizplus · Accepted Answer

In negative control, the lac operon is switched off in the absence of an inducer because the repressor, synthesized by the lacI gene that binds to the operator, physically blocks the transcription of structural genes. When an inducer, such as lactose or allolactose, is present, it binds to the repressor and prevents it from binding to the operator, allowing transcription to occur. Therefore, the presence of an inducer prevents the repressor from binding to the operator, resulting in the activation of transcription of the lac operon.

In Negative Control of Transcription by the Lac Operon, How