Question at position 7 The binding of lactose to the lac repressor:causes an allosteric change in the lac repressor that prevents its binding to its cognate operator.causes an allosteric change in the lac repressor that promotes its binding to its cognate operator.causes an allosteric change in the lac repressor that promotes recruitment of CRP, which in turn promotes the activity of RNA polymerase.All of the abovecauses an allosteric change in the lac repressor that promotes recruitment of RNA polymerase.

Question

Question at position 7 The binding of lactose to the lac repressor:causes an allosteric change in the lac repressor that prevents its binding to its cognate operator.causes an allosteric change in the lac repressor that promotes its binding to its cognate operator.causes an allosteric change in the lac repressor that promotes recruitment of CRP, which in turn promotes the activity of RNA polymerase.All of the abovecauses an allosteric change in the lac repressor that promotes recruitment of RNA polymerase.

BlackTom AI · Accepted Answer

Starting with the context, lactose binding to the lac repressor (LacI) is classically known to induce an allosteric change that reduces LacI's affinity for the lac operator, thereby allowing RNA polymerase access and transcription to proceed.
Option 1: 'causes an allosteric change in the lac repressor that prevents its binding to its cognate operator.' This aligns with the canonical model: lactose (via allolactose) binds LacI, altering its conformation so LacI cannot effectively bind the operator, derepressing the operon. This is a true and fundamental statement about the lac operon regulation.
Option 2: 'causes an allosteric change in the lac repressor that promotes its binding to its cognate operator.' This directly contradicts the established mechanism. Lactose binding relieves repression by reducing operator binding, not by increasing it, so this option describes the opposite effect and is incorrect.
Option 3: 'causes an allosteric change in the lac repressor that promotes recruitment of CRP, which in turn promotes the activity of RNA polymerase.' The lac operon regulation involves CRP-cAMP as an enhancer when glucose is low, but lactose-induced derepression via LacI is independent of CRP recruitment being driven by LacI’s allosteric change. This option combines two separate regulatory influences in a way that inaccurately attributes CRP recruitment directly to LacI’s lactose-induced change.
Option 4: 'All of the above' would require all prior statements to be true. Since option 2 is incorrect (it asserts increased operator binding) and option 3 describes an indirect CRP recruitment mechanism not driven by LacI’s lactose-induced allosteric change, this cannot be correct.
Option 5: 'causes an allosteric change in the lac repressor that promotes recruitment of RNA polymerase.' While derepression enables RNA polymerase access, the statement specifically claiming that LacI’s allosteric change recruits RNA polymerase is not accurate; RNA polymerase recruitment is not caused by the LacI allosteric change but by the removal of repression allowing transcription machinery to engage at the promoter. This makes option 5 incorrect.
In summary, option 1 correctly captures the core effect of lactose binding to LacI, while options 2, 3, 4, and 5 each introduce incorrect mechanisms or overstatements about CRP recruitment and RNA polymerase recruitment that do not reflect the established lac operon regulation.

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