Is the lac operon transcribed when lactose is present?
A) Yes, lactose is converted to another sugar that binds to the repressor, freeing the promoter region.
B) Yes, lactose binds to RNA polymerase, allowing it to bind to the promoter and transcribe the operon.
C) No, lactose is converted to another sugar that binds to the two operators preventing transcription.
D) No, lactose has no effect on transcription of the lac operon.
E) No, lactose binds to the second operator, blocking transcription by RNA polymerase.

Question

Is the lac operon transcribed when lactose is present?  
A) Yes, lactose is converted to another sugar that binds to the repressor, freeing the promoter region.
B) Yes, lactose binds to RNA polymerase, allowing it to bind to the promoter and transcribe the operon.
C) No, lactose is converted to another sugar that binds to the two operators preventing transcription.
D) No, lactose has no effect on transcription of the lac operon.
E) No, lactose binds to the second operator, blocking transcription by RNA polymerase.

Quizplus · Accepted Answer

When lactose is present, it is converted to allolactose, which binds to the repressor protein, causing it to no longer bind to the operator site. This allows RNA polymerase to bind to the promoter and transcribe the genes. So, in the presence of lactose, the lac operon is transcribed.

Is the Lac Operon Transcribed When Lactose Is Present