Question

The lac operon is transcribed when ______.

Options

• lactose is needed by the cell.

• lactose is available to the cell.

• lactic acid is needed by the cell.

• lactic acid is available to the cell.

Answer 1

The lac operon is transcribed when lactose is available to the cell.

Explanation:

The lac operon is a system that allows bacteria to save energy by only making lactose-digesting enzymes when they are actually needed. When lactose is present in the environment, it acts as an inducer by binding to a repressor protein and pulling it off the DNA. This “unblocks” the gene, allowing RNA polymerase to move forward and begin transcription. Once the lactose is all used up, the repressor reattaches, turning the system back off.