Final answer:
The claim that cAMP decreases the affinity of CRP for a DNA site near the lac operon promoter is false; cAMP actually increases CRP's DNA-binding affinity, promoting transcription of the lac operon when glucose is low.
Step-by-step explanation:
The statement in question is false. cAMP actually increases the affinity of CRP (catabolite activator protein), also known as CAP, for a DNA site near the lac operon promoter. When glucose levels are low, cellular cAMP increases, and the cAMP binds to CAP. This cAMP-CAP complex then binds to a DNA site near the lac operon promoter, increasing the binding ability of RNA polymerase to the promoter region and thus initiating transcription of the operon involved in lactose metabolism.
This positive regulation mechanism described is crucial for efficient cellular use of lactose when glucose, the preferred energy source, is not available.The claim that cAMP decreases the affinity of CRP for a DNA site near the lac operon promoter is false; cAMP actually increases CRP's DNA-binding affinity, promoting transcription of the lac operon when glucose is low.