Answer to Question #104874 in Molecular Biology for Kylie

Question

If glucose is absent, but so is lactose, the lac operon will be ________.
1. activated
2. repressed
3. activated, but only partially
4. mutated

Answer 1

Repressed

No transcription of the lac operon occurs. cAMP levels are high because glucose levels are low, so CAP is active and will be bound to the DNA. However, the lacrepressor will also be bound to the operator (due to the absence of allolactose), acting as a roadblock to RNA polymerase and preventing transcription.