What is the likely effect of each of the following mutations o...

Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

Region 4 is deleted.

Accepted Answer

Hi, everybody. Let's look at our next problem. It says which one of the following mutations would lead to higher attenuation control over the trip to fan operon choice A, a deletion of the attenuated stem loop choice B A mutation that stabilizes the anti terminator stem loop choice C A mutation that destabilizes the anti terminator stem loop or choice D A deletion of the region encoding the leader peptide. Well, let's think through this, remembering that we're trying to figure out which situation would lead to higher attenuation control. So transcription stopping of those trip to fan jeans. Now, this can be a little complicated to think through because strip Toan attenuation is a rather complicated process with a liter peptide, two alternate stem loop formations. Um that can be a little tricky to keep everything straight. However, we have some help in the way our answer choices are phrased and I'm going to work my way through them and we can let these kind of straightforwardly lead us to the correct answer while not dealing with the most complicated one of them. And I'll get to that. So we look at choice. A it says a deletion of the attenuated stem loop. Well, we don't have to remember whether it's the 23 stem loop or the 34 stem loop. If we're hurrying through a test, working hard, trying to remember because right there it tells us it's the attenuated stem loop. So the attenuated stem loop is of course, the structure that leads to attenuation that causes transcription to halt. So if we delete the attenuated, that would mean that we have no attenuation, we are missing the structure that causes that to happen. So we're looking for higher attenuation of choice, they can definitely not be our correct answer. Then let's look down at choice B A mutation that stabilizes the anti terminator stem loop. Well, again, right there, it's labeled as the anti terminator that stem loop causes transcription to continue on. And of course, if we stabilize that anti terminator stem loop, we're going to cause less attenuation because we've stabilized the structure that results in the opposite situation. So less attenuation, if we stabilize the anti terminator. So Jo B also definitely not our answer. Now, let's look at choice C A mutation that destabilizes the anti termination terminator stem loop. Well, again, if we destabilize the anti terminator, that would result in more attenuation. If we destabilize the anti terminator, we'd be more likely to form the attenuated stem loop leading to more attenuation. Oops accidentally wrote more attenuation in red, but that's confusing since that's not what we want whereas more attenuation is exactly what we want. So I've changed it to blue to remind us that we are looking for this. We want to look for the situation that will give us higher levels of attenuation. So if we destabilize the anti terminator stem loop, we'll have more attenuation. And therefore that leads us to choice C as our answer. Now on a test, I've got a correct answer. Only one answer. Choice is correct. I don't have to deal with choice D but we're talking through these answers to understand them. So I will deal with choice D. But you can see why I was a little eager to avoid it if I were in a hurry because choice D is the most complicated one to think through. It says a deletion of the region encoding the leader peptide. So we need to think through the R the relation of that leader peptide to attenuation. So we recall in our situations of low levels of crypto fan. So down arrow tripp toan, the ribosome stalls during translation of the leader peptide. And that's because that leader peptide gene has two trip to fan residues that it needs or two codons for trip to fan residues. So if tripp to fan levels are low, it's got to wait a while before it can get those two trip to fans. So it's stuck there as a result of that ribosome stalling the M R N A further down forms a 23 stem loop. So 23 stem loop forms and that 23 stem loop is the anti terminator stem loop when we form that transcription continues. And by the very definition of that, we have lower attenuation in the opposite situation where we have high levels of crypto fan. So I put up arrow and then Tripp Toan, the ribosome continues, it doesn't have to stall. There's plenty of trip to fan around to let it synthesize the whole li peptide and go on its merry way. As a result, the ribosome blocks region two, it's sitting there on region two, having continued along and finished the leader peptide. When region two is blocked, instead, we form the 34 stem loop. So the 34 stem loop forms and this is the attenuated stem loop. So we've formed the attenuated stem loop transcription is terminated. And so our overall situation is one of higher attenuation. So here's our situation of lower or higher attenuation. So let's think about what would happen if the whole region with the code for the leader peptide is missing. Well, in that case, the ribosome won't be going along there at all. We don't have a region that's coating for a protein. If there's no ribosome present, then there's no blocking of region two. So I'm going to put an arrow to the situation up top where I said the 23 stem loop forms, which is the anti terminator, I'll say no ribosome blocking region two. So the 23 stem loop forms, which is the anti terminator structure transcription continues and you have lower attenuation. So that's why choice D is not our answer because a deletion of that region means we won't have the ribosome moving along and we'll have a situation of lower attenuation which is not what we're looking for. So which mutation leads to higher attenuation control choice C A mutation that destabilizes the anti terminator stem loop. See you in the next video.

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.
Region 4 is deleted.

Key Concepts

Attenuation in Gene Regulation

trp Operon Structure

Role of Region 4 in Attenuation

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