Positive Control by cAMP & CRP

Jason Amores Sumpter
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So from our previous lesson videos, we know that cyclic A, M, p or C amp will increase the rate of lack operation transcription. But in this video, we're going to talk about exactly how that works by focusing on positive control by C. Amp. And a molecule that we're going to introduce called CRP. And so CRP is really just an abbreviation for cyclic MP receptor protein or just CRP for short. And CRP is actually an activator protein, which recall from our previous lesson videos. Activator proteins are regulatory proteins that will stimulate transcription. And so CRP is an activator protein that will stimulate the lack opera in transcription when CRP is bound to see AMP. And so you can see that even embedded in CRP s full name here it has cyclic GMP. And so it does rely on C amp okay. And so recall from our previous lesson videos that low glucose levels is going to translate to high cellular C AMP levels and high cellular C AMP levels is going to allow C AMP to bind and activate C. R. P. And an active CRP is going to act as an activator protein, and it's going to bind to a region of D N a upstream of the lack promoter. And it is going to stimulate transcription by helping to recruit RNA polymerase. And when the RNA polymerase is recruited and bound to the promoter, then transcription is stimulated and can proceed. And so, essentially, what we're saying here is that when glucose levels are low, if we have low glucose, that's going to translate to having high cm and having high C amp is going to allow c amp to bind to and activate, uh, CRP. So we have an active CRP, and having an active CRP is going to increase the rate of lack Operation transcription. And so, really, this here this line here shows you the takeaway that low glucose levels leads to high C AMP levels high C AMP levels leads to an active CRP, and an active CRP increases the rate of lack Operation transcription. And so let's take a look at our image down below to get a better understanding of how C AMP and CRP positively control expression of the lack opera and its positive control. Because it is increasing in turning on the lack opera and so that's what we're focusing on in this image is positive control of the lack opera, mainly by an active CRP protein. And so, if we take a look at our image down below, notice that we have it broken up into two halfs. We have the top half here, and then we have the bottom half down below. Uh, we'll focus on the top half first, and what you'll notice is that we're showing you the lack opera on over here. But this time notice that the lack opera has a new region that we have not yet introduced, and we're showing it here for the first time. And that is the CRP binding site. And so the CRP binding site is the site that is upstream of the promoter. Uh, that is going to be where the active CRP will bind. And so notice that, uh, in the top half of this image, we have some specific conditions indicated by this box over here, and so notice that lactose levels are high. Glucose levels are also high. And of course, we know that C. Amp. Is going to have an inverse relationship to the glucose levels. And so if glucose levels are high. That means that C amp levels must be low. And so notice here you can see that there's glucose here in the sell these little green hexagons and you can also see that there is lactose within the cell. And we know already that lactose, a derivative of lactose, will bind to the lack repressor lack I and inactivate the Lac Repressor. But also, when glucose is present, uh, glucose is going to lead to having low levels of C M and low levels of cm means that the inactive we're going to have an inactive CRP protein and the inactive CRP protein will not bind to the CRP binding site. And so all of these conditions means that the RNA preliminaries, even though it's not being blocked by the inactive lack repressor, it will not be able to bind to the promoter very effectively without the, uh, the active CRP here. And so the inactive CRP is not going to bind. And we need this act this crp to bind in order for RNA preliminaries to also bind. And so what we're seeing here is that, uh, transcription of the lack opera is off in this state here, So the lack opera is in an off position here under these conditions. And again, this makes sense because we know that glucose is the preferred energy source. And so if there are high levels of glucose, then that means that the cell is going to be using glucose as the energy source. And it should not waste energy transcribing the lack opera. Because even though lactose is high, it's not going to be using lactose as the energy source. It's going to be using glucose as the energy source here. Now notice down below. In this image, we have some slightly different conditions. Notice that the lactose concentration levels are still high, just as they were before. Okay, so lactose levels are still high, but this time notice that the glucose concentration levels are low. And again, we know that C. Amp has an inverse relationship with glucose levels, and so glucose levels are low. That means that C AMP levels are going to be hi, and so you can see here in this image that c amp. This little green molecule, its concentration is high. And when it is high, C AMP is going to bind to CRP, and when C and binds to CRP, it activates CRP. So we have an active CRP, and the active CRP will bind to this CRP binding site. And the active CRP bound to the CRP binding site is going to help to recruit the RNA proliferate so that the RNA preliminaries will actually bind. And if the RNA polymerase is bound, then it can proceed forward with transcription and activate all of these genes. And so what we have and here is a lack opera, and that is on, and transcription and gene expression is on in comparison to the lack opera and being off in the above half of the image. And so notice that the lack opera, uh, not only does it require lactose levels to be high to inactivate the lack repressor, but it also requires glucose levels to be low so that C. Amp can activate CRP and CRP combined and recruit RNA preliminaries and RNA polymerase can stimulate transcription. And so this year concludes our brief introduction to positive control by C. AMP. And CRP, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video