Regulation of Gene Expression

AP Biology· difficulty 2/5

The lac operon is shown with the lac repressor bound to the operator in the absence of lactose.

P promoter O operator lacZ lacY lacA repr No lactose: repressor on operator Operon OFF

What direct effect does the binding of allolactose to the lac repressor have?

  • A

    It causes the repressor to release the operator, allowing transcription of lacZ, lacY, and lacA.

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  • B

    It triggers degradation of the repressor mRNA.

  • C

    It activates the repressor, increasing operator binding.

  • D

    It binds the promoter to recruit RNA polymerase.

Explanation

Allolactose, the inducer derived from lactose, binds the lac repressor and changes its conformation; the repressor releases the operator and RNA polymerase can transcribe the lac structural genes.

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