How is lac operon transcription regulated by the presence or absence of lactose?
A) When lactose is available, the repressor will bind to allolactose instead of blocking RNA polymerase by binding to the operator.
B) When lactose is not available, the repressor will bind to the promoter and block RNA polymerase from binding to the promoter.
C) When lactose is not available, the repressor will bind to allolactose.
D) When lactose is available, allolactose is produced and binds to the operator, blocking RNA polymerase.
E) In the absence of lactose, transcription occurs at a low level, resulting in the production of allolactose, which, in turn, stimulates the cell to take up lactose.

Question

Quizplus · Accepted Answer

When lactose is present, it is converted into allolactose, which then binds to the repressor. This binding changes the shape of the repressor, preventing it from binding to the operator. As a result, RNA polymerase can transcribe the genes involved in lactose metabolism.

How Is Lac Operon Transcription Regulated by the Presence or Absence