In the lac operon, the repressor inhibits transcription when a. the repressor is bound to the inducer. b. the repressor is not bound to the inducer. c. the repressor is bound to glucose. d. the repressor is not bound to the operator.

Verified step by step guidance

1. Understand the function of the lac operon: The lac operon is a set of genes in bacteria that are involved in the metabolism of lactose. It is regulated by several components including the repressor protein, which plays a crucial role in controlling the transcription of the operon.
2. Identify the role of the repressor: The repressor protein can bind to the operator region of the lac operon, thereby blocking RNA polymerase from transcribing the downstream genes necessary for lactose metabolism.
3. Consider the effect of the inducer on the repressor: The inducer (allolactose, a derivative of lactose) binds to the repressor. When the inducer is bound to the repressor, it causes a conformational change in the repressor.
4. Analyze the conformational change: This change in shape of the repressor reduces its affinity for the operator region, preventing it from binding effectively.
5. Conclude the correct condition for inhibition: Since the binding of the inducer to the repressor prevents the repressor from binding to the operator, transcription is inhibited when the repressor is not bound to the inducer.