Under low glucose conditions, what is the role of the CAP-CAMP complex?

• A. When glucose is high, cAMP levels rise and CAP activates transcription.
• B. When glucose is low, cAMP rises and CAP-CAMP enhances transcription.
• C. CAP-CAMP represses transcription irrespective of glucose.
• D. cAMP levels decrease when glucose is low.

Answer: (B)

In bacteria, gene transcription is regulated by the CAP-cAMP system to coordinate metabolism with available nutrients. When glucose is scarce, adenylate cyclase activity increases and cAMP levels rise. cAMP then binds to CAP, and the CAP-cAMP complex binds to promoter regions of certain operons (like those for utilizing alternative sugars) to recruit RNA polymerase more effectively, boosting transcription. This is why the statement that matches the scenario is: under low glucose, cAMP rises and CAP-CAMP enhances transcription.

Other options miss the key relationship: high glucose lowers cAMP and keeps CAP inactive, so transcription isn’t enhanced; CAP-CAMP acts as an activator rather than a universal repressor; and cAMP does not decrease when glucose is low.