Question

A mutation that renders the regulatory gene of a repressible operon non-functional would result in:

Options

• excessive synthesis of a catabolic activator protein.

• irreversible binding of the repressor to the promoter.

• inhibition of transcription of the structural genes.

• continuous transcription of the structural genes.

Answer 1

continuous transcription of the structural genes.

Explanation:

In a repressible operon (like the trp operon), the regulatory gene produces a repressor protein that is normally inactive but can bind to the operator to shut off transcription when a specific molecule is present. If the regulatory gene is rendered non-functional by a mutation, no repressor protein is produced at all. Without a functional repressor to block RNA polymerase, the operon remains permanently “on,” leading to the uninterrupted and continuous transcription of the structural genes.