Which one of the following accurately describes the Lac operon? A. RNA polymerase is prevented from transcribing the lac genes when lactose is present. B. The repressor protein binds to the operator when lactose is present. C. The repressor is freed from the operator when lactose is present. D. RNA polymerase transcribes the lac genes when lactose isn't present

Question

02-04-2019
Biology

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Which one of the following accurately describes the Lac operon? A. RNA polymerase is prevented from transcribing the lac genes when lactose is present. B. The repressor protein binds to the operator when lactose is present. C. The repressor is freed from the operator when lactose is present. D. RNA polymerase transcribes the lac genes when lactose isn't present

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BioWizard BioWizard · Answer 1 · 2019-04-06T12:06:10+02:00

The correct answer is: C. The repressor is freed from the operator when lactose is present

The lac operon is found in bacteria (E. coli) and it contains genes involved in lactose metabolism which are expressed only when lactose is present and glucose is absent. Lac operon is regulated and can be turned on and off thanks to regulators: lac repressor and catabolite activator protein (CAP).

The lac repressor blocks transcription of the operon when there is no lactose (it binds to operator so RNA polymerase cannot bind to the promoter). When lactose is present, (repressor is a lactose sensor), the repressor is freed from the operator.

CAP, on the other hand, acts as a glucose sensor- activates transcription when glucose levels are low.