How does the Lac operon function in prokaryotes?

The Lac operon is a well-studied example of gene regulation in prokaryotes, specifically E. coli, and it plays a crucial role in the metabolism of lactose. The correct answer indicates that the operon regulates the metabolism of lactose depending on the availability of glucose.

When lactose is present, it acts as an inducer that binds to the repressor protein, allowing RNA polymerase to transcribe the genes necessary for lactose metabolism. This mechanism ensures that the enzymes needed to metabolize lactose (such as β-galactosidase) are produced only when lactose is available. However, the presence of glucose takes precedence in the operon's regulation. When glucose is abundant, an alternative signaling pathway inhibits the operon, preventing the expression of lactose-metabolizing enzymes.

This dual regulation mechanism allows the cell to efficiently manage its resources, using glucose as a primary energy source, while only activating lactose metabolism when glucose is scarce. Thus, the Lac operon allows E. coli to prioritize glucose over lactose and to use lactose only when it is favorable to do so. This is why the chosen answer correctly reflects the operon's function in regulating lactose metabolism in response to glucose levels.