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In the lac operon, transcription of the lac genes is induced by
Aglucose binding the repressor
Bthe ribosome moving onto the operator
Cthe operator detaching from the promoter spontaneously
Dlactose binding and inactivating the repressor
Answer & Solution
Correct answer: D. lactose binding and inactivating the repressor
When lactose is present, an inducer (allolactose) binds the lac repressor and changes its shape so it can no longer sit on the operator. RNA polymerase is then free to transcribe lacZ, lacY and lacA — the lactose-digesting genes.
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