Which best describes the function of the lac operon?

The lac operon is a well-studied genetic system in bacteria, particularly in Escherichia coli, that allows the organism to metabolize lactose when it is present in the environment. The operon consists of genes that encode the proteins necessary for the transport and breakdown of lactose into glucose and galactose, which can then be utilized as energy sources.

When lactose is available, it binds to the repressor protein, causing it to change shape and detach from the operator region of the operon. This removal of the repressor allows RNA polymerase to access the promoter and initiate transcription of the genes responsible for lactose metabolism. Hence, the primary function of the lac operon is to enable bacteria to efficiently utilize lactose as an energy source, particularly when other sources of energy, like glucose, are scarce. This adaptive mechanism highlights the lac operon's role in the regulation of gene expression in response to environmental changes, which is fundamental to cellular metabolism.