What Transcription of lactose metabolizing genes is blocked?

The transcription of lactose metabolizing genes, specifically the genes involved in the lac operon (such as lacZ, lacY, and lacA), is blocked in the presence of glucose. This phenomenon is known as catabolite repression, where the presence of glucose inhibits the synthesis of cyclic AMP (cAMP). Low levels of cAMP result in reduced binding of the cAMP-CRP complex to the promoter region of the lac operon, preventing the transcription of lactose-utilizing enzymes. Consequently, the cell prioritizes glucose metabolism over lactose when both sugars are available.