Question

Read the statements regarding the lac operon and choose the correct option
I. An inducer regulates the switching on and off of lac operon.
II.Repressor protein dissociates from operator region and prevents RNA polymerase from transcribing the operon.
III. In the presence of lactose, the repressor is activated by interaction with lactose.
IV. RNA polymerase has access to the promoter and transcription proceeds only when the repressor is inactivated.

• A. I and IV are correct
• B. Only II is correct
• C. III and IV are correct
• D. I and III are correct

Answer 1

The correct option is A I and IV are correct

The lac operon contains genes involved in lactose metabolism. It's expressed only when lactose is present and glucose is absent.

When lactose is available, some molecules will be converted to allolactose inside the cell. Allolactose binds to the lac repressor and makes it change shape so it can no longer bind DNA.
The lac repressor acts as a lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. Now the RNA polymerase has access to the promoter and the transcription proceeds. So the statements I and IV are correct for lac operon.