Which operon is involved in the metabolism of lactose in E. coli?

The lac operon is crucial in the metabolism of lactose in E. coli. It encodes the genes necessary for the transport and breakdown of lactose into glucose and galactose, allowing the bacteria to utilize lactose as an energy source when glucose is not available. The operon includes three structural genes: lacZ, which encodes beta-galactosidase that breaks down lactose; lacY, which encodes lactose permease that facilitates the entry of lactose into the cell; and lacA, which encodes thiogalactoside transacetylase, although its exact role in lactose metabolism is less clear.

When lactose is present, it binds to the repressor protein, causing a conformational change that reduces its affinity for the operator region of the operon. This alleviates transcriptional repression and allows RNA polymerase to transcribe the lac operon genes, leading to the production of the enzymes needed for lactose catabolism.

In contrast, the other operons mentioned—such as the trp operon, which is involved in tryptophan biosynthesis; the his operon, related to histidine biosynthesis; and the ara operon, which is implicated in the metabolism of arabinose—are involved in