Which of the Following Statements is True Regarding the Lac

Question

Which of the following statements is true regarding the lac operon?
A) The repressor binds to the promoter element.
B) Transcription is initiated by the binding of the inducer to the promoter.
C) The lac operon is unique because it is not subject to catabolite repression.
D) The promoter element is not essential for the transcription of the operon.
E) lacZ, lacY and lacA gene products are synthesized at low levels in the uninduced state.

Accepted Answer

In the uninduced state, the lac operon is not actively transcribed, and therefore, lacZ, lacY, and lacA gene products are synthesized at low levels. The lac repressor binds to the operator element, not the promoter element, to prevent transcription. The binding of an inducer, such as lactose or allolactose, to the repressor protein causes a conformational change that leads to dissociation of the repressor from the operator, allowing RNA polymerase to bind to the promoter and initiate transcription. The lac operon is subject to catabolite repression, which is mediated by the presence of high levels of glucose and involves the cAMP-CAP regulatory system. The promoter element is essential for the transcription of the operon because it is the site where RNA polymerase binds to initiate transcription.