Question

What is the role of the catabolite activator protein (CAP) in the regulation of the lac operon?

a. CAP binds to the promoter in the absence of glucose, promoting transcription
b. CAP binds to the operator in the presence of glucose, promoting transcription
c. CAP binds to the promoter in the presence of glucose, promoting transcription
d. CAP modifies histones to make RNA Pol accessible to the DNA
e. CAP binds to the operator in the absence of glucose, promoting transcription

Answer 1

CAP acts as a transcriptional activator for the lac operon by binding to its promoter region in the absence of glucose, enhancing the binding of RNA polymerase, and hence promoting transcription when lactose is available.

Step-by-step explanation:

The role of the catabolite activator protein (CAP) in the regulation of the lac operon is vital for the utilization of lactose when glucose is not available. CAP, a transcriptional activator, binds to the promoter region of the lac operon when cellular levels of cAMP rise, which occurs in the absence of glucose. As a result, when lactose is present (and hence, freeing the operator region from the lac repressor), and glucose levels are low, the cAMP-bound CAP facilitates the binding of RNA polymerase to the promoter, thereby promoting transcription of the lac operon and enabling the utilization of lactose as an energy source.