In the lac operon, which of the following functions does the lactose molecule serve:

• A. It is the corepressor molecule.
• B. It is the repressor molecule.
• C. It is the inducer molecule.
• D. It serves no function in regulating the lac operon.

Answer: (C)

Verified step by step guidance

1. Understand the role of the lac operon: The lac operon is a set of genes in bacteria that are involved in the metabolism of lactose. It is a classic example of gene regulation in prokaryotes.
2. Identify the components of the lac operon: The lac operon includes the promoter, operator, and structural genes (lacZ, lacY, and lacA). The repressor protein binds to the operator to prevent transcription.
3. Define the role of lactose: Lactose acts as an inducer molecule. When lactose is present, it binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator.
4. Explain the effect of lactose binding: When lactose binds to the repressor, the repressor is unable to bind to the operator. This allows RNA polymerase to access the promoter and transcribe the structural genes, leading to the production of enzymes that metabolize lactose.
5. Conclude the function of lactose: By binding to the repressor and preventing it from inhibiting transcription, lactose serves as an inducer molecule, facilitating the expression of genes necessary for lactose metabolism.