Which two substances regulate the Lac operon?

The regulation of the Lac operon, which is a model for understanding gene regulation in prokaryotes, primarily involves lactose and glucose. Lactose is the substrate that induces the operon by binding to the repressor protein, removing it from the operator region and allowing for transcription of the structural genes that code for enzymes needed to metabolize lactose.

On the other hand, glucose plays a crucial role in catabolite repression, where the presence of glucose inhibits the expression of the Lac operon. When glucose levels are high, the cellular levels of cAMP (cyclic AMP) are low. cAMP is necessary for the activation of CAP (catabolite activator protein), which enhances the binding of RNA polymerase to the promoter of the Lac operon. Thus, low glucose leads to higher cAMP levels, which stimulates the expression of the Lac operon.

Together, lactose and glucose interact within the regulatory framework of the Lac operon to control the expression of genes necessary for lactose metabolism, making them the primary substances involved in its regulation.