Final answer:
The assertion that cAMP binds to the Lac repressor is false. Instead, cAMP binds to CAP, which then binds to the lac operon promoter to aid in transcription when glucose levels are low and lactose is available as an energy source.
Step-by-step explanation:
The statement that cAMP binds to the Lac repressor, decreasing its affinity for a DNA site near the lac operon promoter, is false. cAMP actually binds to the catabolite activator protein (CAP), also known as the cAMP receptor protein (CRP), not the Lac repressor. When glucose levels are low in the cell, the levels of cAMP rise, causing it to bind to CAP. The cAMP-CAP complex then binds to the promoter region of the lac operon, aiding RNA polymerase in initiating transcription. For the lac operon to be expressed, allolactose must bind to the Lac repressor, causing it to dissociate from the operator site, thereby permitting transcription of the operon genes.
The statement is false. cAMP does not bind to the Lac repressor; rather, it binds to catabolite activator protein (CAP) or CAMP receptor protein. The binding of cAMP-CAP complex to a specific site on the promoter region of the lac operon increases the binding ability of RNA polymerase, resulting in the initiation of transcription of the structural genes. This mechanism allows for the expression of the lac operon when glucose levels are low and lactose is present.