Question

Which statement is NOT true about the repressor protein, in regard to the lac operon:

Group of answer choices

it blocks transcription when it is bound to the operator

is only expressed when glucose is present

it changes its three-dimensional shape (conformation) when it is bound to the inducer, allolactose

All listed ARE true about the repressor

binds to the operator region of the lac operon when glucose is being utilized

Answer 1

All listed are true about the repressor. (Lac operon is an inducible operon which is induced to get switched on when there is high lactose and low glucose in the surrounding of E. coli bacteria. Allolactose(isomer of lactose) is the inducer and it binds with the repressor protein (which would bind to operator and block transcription if allolactose was not present and glucose was high) resulting in a conformational change in the protein which inhibits it to bind to operator. This allows the transcription to occur and the enzymes are formed which breaks down the lactose into glucose. When glucose is enough and lactose becomes low the repressor gets free and again binds to operator thereby inhibiting the transcription and the enzyme production because they are now not needed. Lac operon is off in this case. When glucose gets low, and if lactose is present (which is inducer) it again is switched on and the whole process occurs.

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