How does glucose availability influence lac operon expression via cAMP and CRP?

How does glucose availability influence lac operon expression via cAMP and CRP?

• A. When glucose is low, cAMP levels rise and bind CRP to form CRP-cAMP that binds the promoter and enhances transcription.
• B. When glucose is low, cAMP levels fall, reducing transcription.
• C. CRP-cAMP activates transcription regardless of glucose levels.
• D. Glucose directly binds RNA polymerase to increase transcription.

Answer: (A)

When glucose is scarce, the cell raises cAMP levels. cAMP binds to CRP (CAP), and the CRP-cAMP complex attaches near the lac promoter. This interaction helps RNA polymerase bind more effectively, boosting transcription of the lac operon. This activator-mediated increase occurs especially when lactose is available to relieve the LacI repressor, allowing the operon to be expressed more. If glucose is abundant, cAMP levels fall, CRP-cAMP cannot form, and transcription is not strongly activated. Glucose does not directly bind RNA polymerase, so that option is incorrect.

When glucose is scarce, the cell raises cAMP levels. cAMP binds to CRP (CAP), and the CRP-cAMP complex attaches near the lac promoter. This interaction helps RNA polymerase bind more effectively, boosting transcription of the lac operon. This activator-mediated increase occurs especially when lactose is available to relieve the LacI repressor, allowing the operon to be expressed more. If glucose is abundant, cAMP levels fall, CRP-cAMP cannot form, and transcription is not strongly activated. Glucose does not directly bind RNA polymerase, so that option is incorrect.