How would a cap⁻ mutation that produces an inactive CAP ...

Question

How would a cap⁻ mutation that produces an inactive CAP protein affect transcriptional control of the lac operon?

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. Which of the following statements about C A MP and CCAP is incorrect. Choice A without C A MP cap cannot bind to DNA and remains inactive. Choice B when C A MP levels are low and glucose levels are high, cap is active and binds DNA. Choice C cap is only active when C A MP levels are high and glucose levels are low and choice D both A and B. So let's think about C A MP and C and this system remembering that we're looking for an incorrect statement and keeping in mind that we have that choice D which would say that both A and B are incorrect. So C A MP and cap, as we recall are part of the um positive regulation of the LAC operon. So they're involved in turning up the level of transcription and they work by causing transcription to be increased when glucose levels are low. So again, the whole lack operon system is oriented around producing the genes that help to digest lactose. And you only want those genes produced when lactose is present and glucose is absent since glucose is a better energy source for the cell. So we're starting by thinking about, we want to think about when glucose levels are low, you want this transcription turned up. So when glucose levels are low, that causes C A MP levels to rise D A MP then binds to the cap protein metabolite activator protein. This cap then is activated. So we'll say activate it after binds to cap and the activated cap binds to the cap binding site which results in it eating the RN A polymerase to bind more tightly to the promoter with the results that transcription is increased. So that's the whole system. We want to think about when we evaluate these answer choices again, remembering we're looking for the incorrect choice. So choice A says without C AM PC cannot bind to DNA and remains inactive. Well, this is a true statement because cap binds to the DNA only when activated by having C A MP bound to it. So we're going to eliminate choice A since we're looking for an incorrect statement. Therefore, we can also eliminate Choice BD, excuse me, choice D, which is both A and B since A is incorrect. So let's look at Choice B, it says when C A MP levels are low and glucose levels are high cap is active and binds DNA. Well, this is incorrect cap is active when C A MP levels are high and glucose levels are low. So Choice B is correct. We've already eliminated the choice that involves more than one incorrect statement. So we can pick B as our answer. But to be thorough, we'll look at choice C to C says cap is only active when C A MP levels are high and glucose levels are low. Well, this is true that is when cap gets activated by binding to C A MP. And so C is not our answer. So once again, which of the following statements is incorrect choice. B when C A MP levels are low and glucose levels are high cap is active and binds DNA. See you in the next video.

How would a cap⁻ mutation that produces an inactive CAP protein affect transcriptional control of the lac operon?

Key Concepts

CAP Protein Function

Lac Operon Regulation

Mutation Effects on Gene Expression

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