Which of the following statements accurately describes the lac operon?

• A. It converts glucose to lactose
• B. It contains a repressor and operates in the absence of lactose
• C. It contains the lac Z, lac Y, lac A genes and a repressor
• D. It is only active when glucose is present

Answer: (C)

The lac operon is a well-studied example of gene regulation in prokaryotes, particularly in the bacterium Escherichia coli. Statement C accurately describes the lac operon because it specifies the key components of the operon: it includes three structural genes—lacZ, lacY, and lacA—each of which encode proteins necessary for the metabolism of lactose. LacZ encodes β-galactosidase, which breaks down lactose into glucose and galactose. LacY encodes lactose permease, which facilitates the transport of lactose into the cell. LacA encodes thiogalactoside transacetylase, which is involved in the metabolism of lactose. Additionally, the operon is regulated by a repressor protein, which binds to the operator region and inhibits transcription when lactose is absent.

Understanding the function and structure of the lac operon is essential for comprehending how bacteria respond to environmental changes, particularly in utilizing different sugars for energy. This operon is notably active when lactose is present and glucose is not, allowing the bacterium to adapt to resource availability.