Which statement correctly describes an inducible operon?

• A. Transcription is always on regardless of effectors
• B. The inducer permanently inactivates the operon
• C. Binding of an inducer will turn on transcription
• D. Binding of a repressor will turn on transcription

Answer: (C)

Inducible operons are off by default because a repressor sits on the operator and blocks transcription. When the inducer binds to this repressor, the repressorChanges shape and can no longer bind to the operator. That removal of repression allows RNA polymerase to transcribe the operon. So, the key idea is that the presence of the inducer activates transcription by disabling the repressor. This aligns with the statement that binding of an inducer will turn on transcription.

This differs from the other scenarios: transcription isn’t always on, the inducer doesn’t permanently shut down the operon, and binding of a repressor generally blocks transcription rather than turning it on.