What Happens in the Lac Operon When Both Lactose and Glucose

Question

What happens in the lac operon when both lactose and glucose are present in the environment?
A) Transcription of the lac operon structural genes will occur.
B) Transcription of the lac operon structural genes will occur but at a very slow rate.
C) Transcription of the lac operon structural genes will occur at an increased rate.
D) Transcription of the lac operon will not occur because the inducer is not present in the environment.
E) Transcription of the lac operon will not occur because of catabolite repression.

Accepted Answer

When both lactose and glucose are present, glucose will be used as the primary energy source by the cell. This results in catabolite repression, where the lac operon is not transcribed even though lactose is present. Therefore, the correct answer is E.