Glucose's Impact on Lac Operon - Video Tutorials & Practice Problems
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concept
Glucose Levels, cAMP, & the Lac Operon
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5m
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in this video, we're going to begin. Our lesson on glucose is impact on the lack opera, and so we're going to focus on glucose levels, a molecule called C amp. And how they affect the lack opera. And so what's important to note is that in most precarious, glucose is actually the preferred energy source, even in the presence of lactose. And so what this means is that if glucose is available to cells, then the cells are going to be using glucose as their primary energy source, not lactose, and therefore the lack opera and should be turned off in the presence of glucose. Now it turns out that glucose levels are linked to cellular levels of a molecule that's called cyclic a M p or just C. AMP. For short through a process that we're not going to get into in this video. However, what you should know is that when glucose concentrations are really, really low, or when glucose is just absent and glucose is not available for metabolism, then cellular levels of this molecule, called C hamp are going to increase, and so high cellular C AMP levels will also actually increase the rate of transcription of the lack operas. And so basically, what we're seeing here is when glucose is low or absent. C amp levels increase the rate of transcription of the lack opera, and so the lack opera and will be expressed when glucose is low or absent. But if glucose is available, then the lack opera will be turned off. And so this allows glucose to be used as the preferred in the primary energy source. And lactose will only be used as a secondary energy source when glucose is not available. Now see AMP levels. They actually do not affect the repressor proteins activity, so they do not affect black eyes activity. UH, they only increase transcription of the lack operas when glucose is absent. And as we move forward in our course, we'll we'll be able to talk about exactly how it is that C. Amp affects the lack operations transcription. But for now, let's take a look at this image down below. And so what it's saying here in this example is that glucose levels control C AMP levels in the cell. Uh, and the CFP levels in the cell are going to control the rate of the lack Opteron transcription. And so over here on the left hand side, notice that we have a scenario. We're showing you a cell here. So here is our cell and notice that there is a high glucose concentration. This little green hexagon represents glucose, and there is low lactose concentration. And so notice that on the inside of ourselves, because there is high glucose that actually translates to having low c amp within the cell. And so notice that within ourselves the sea ant molecule which is represented by this little green, uh, circle that we see here. Um, there the C amp levels inside the cell are relatively low when glucose concentrations are high. So there's an inverse relationship there between glucose concentrations and see and concentrations. When one is high, the other is low, and the low C amp is actually going to translate to having low lack opera in transcription. And so the lack operation will not be transcribed at a high rate. It will be low lack opera in transcription when glucose is high and again, this allows glucose to be used as the primary energy source. However, over here on the right hand side, notice that we have a different scenario again. We still have our cell here in the middle. But notice that this time there's a low glucose concentration and a high lactose concentration. And so the low glucose concentration is going to have an inverse relationship with the amount of C. Amp. And so there's going to be a high levels of C AMP within the cell, and so you can see that within our cell down below. Here, all of these little green circles that you see are representing the C. AMP. Molecules. And there are a lot of C amp on over here on this side as compared to over here on this side. And so the high C amp is going to translate to having high lactose opera lack opera in transcription. And so what this allows for is the lactose is going to be used as an energy source when glucose is not available. And so again, this level of regulation allows glucose to be the primary energy source and lactose to be used only as a secondary energy source when glucose is not available. Now, as we move forward in our course, we're going to talk more details about exactly how is it that C amp increases the transcription of the lack opera, But for now, this year concludes our brief introduction to glucose impact on the lack opera, and we'll be able to learn more as we move forward in our course, So I'll see you all in our next video.
2
example
Glucose's Impact on Lac Operon Example 1
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6m
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So here we have an example problem that wants us to complete the table that's down below right here. And notice that this table is showing us the environmental levels of glucose and lactose concentrations, cellular levels of glucose, C amp and lactose concentrations. And then in this last column over here, wants us to determine if the lack opera and is being expressed or not based on the indicated conditions. And so we'll focus on one row at a time here, filling out all of the blanks that we see throughout. And so notice that the first row here has glucose environmental levels being hide and lactose environmental levels being high. So, of course, cellular levels of glucose are also going to be relatively high when environmental levels are high as well, and recall that glucose has an inverse relationship with C AMP levels. And so if glucose concentrations are high, then C AMP levels are going to be low now, of course, if lactose concentration levels on the environment, the outside environment are high, that's also going to translate to lactose levels being high, uh, within the cell as well. Cellular levels of lactose will also be high And so I recall that the lack opera is only going to be expressed when glucose is not available, because glucose is going to be the preferred energy source. And the lack operas should be off when glucose is available. And so notice that glucose levels are pretty high here. And so glucose is available for the cell. And so that means that it will be using glucose as the primary source, even though lactose is available. And so the lack opera is going to be off here. Or we can say that no, the lack opera and will not be expressed Now looking over here, we can see again that glucose concentrations are going to be high this time. Lactose levels are going to be low. And so, of course, having high environmental glucose levels is going to lead to having high cellular glucose levels. And so here we can put in high. And, of course, recall that C. Amp has an inverse relationship with glucose. And so if glucose is high, then C amp levels are going to be low. And, of course, having a low lactose, uh, environmental levels is going to translate to having low cellular lactose and again, under these conditions, the lack opera is only going to be expressed when those genes are needed to break down lactose and again. Because glucose is the preferred source, we know that the lack opera is not going to be expressed in the presence of glucose. It's also not going to be expressed in the absence of LAC tips. And so once again here we have some conditions that say the lack opera and will not be on it will be off under these conditions Now. Next, we have the third row here, which is highlighted in yellow, but we're actually going to skip this row and go to the last row here before we actually go to the yellow Rose. So let's skip that row and we'll come back to it here shortly. Let's focus on the bottom row here. And so notice here that glucose concentrations are low on the environment, and so that's going to translate to glucose cellular levels also being low. And we know that C. Amp has an inverse relationship with glucose. And so if glucose levels are low, C AMP levels are going to be high now. Of course, having low. Lactose in the environment is also going to translate to having low lactose intracellular levels or cellular levels. And so should the lack opera and be expressed, or should it not be expressed? Well, notice that glucose levels are low, so glucose is not going to be available as the primary energy source, but also notice that lactose levels are also low. And so the lack a bronze should only be turned on if lactose is available as well. And so because lactose is low here, the lack opera and should not be expressed. And so once again, we have a scenario that is no. And so now we focus on this third column here that's highlighted in yellow, and what you'll notice is that glucose environmental levels are low, but lactose environmental levels are high. Now. Having low environmental glucose levels is going to translate to having low cellular glucose levels, and C AMP once again has an inverse relationship with glucose levels. And so if glucose levels are low, C AMP levels are going to be high. And, uh, again, if lactose is high on the environment, then lactose is also going to be relatively high and the cellular levels, and so we can say hi here as well. And so under these conditions, should the lack opera and be expressed and here we can say yes. The lack opera in should be expressed under these conditions, because glucose is not available to be the primary energy source and lactose is available. And so these are the conditions that are needed to allow for, uh, lack opera and to be expressed, and also notice that the high cellular C AMP levels are going to lead to the lack opera and being expressed. And again, we're going to talk about exactly how C amp impacts the lack opera in our next lesson video. But for now, this here concludes this example problem, completing this entire table down below. And so we'll be able to get some more practice as we move forward. So I'll see you all in our next video
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Problem
Problem
How does extracellular glucose inhibit transcription of the lac operon?
A
By strengthening the binding of the repressor to the operator.
B
By weakening the binding of the repressor to the operator.
C
By inhibiting RNA polymerase from opening the strands of DNA to initiate transcription.
D
By reducing the levels of intracellular cAMP.
4
concept
Positive Control by cAMP & CRP
Video duration:
8m
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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
5
Problem
Problem
When glucose is present:
A
cAMP is high, CRP binds to the activator binding site, and transcription of the lac operon is turned off.
B
cAMP is low, CRP binds to the site activator binding site, and transcription of the lac operon is turned on.
C
cAMP is high, CRP does not bind to the activator binding site, and transcription of the lac operon is turned on.
D
cAMP is low, CRP does not bind to the activator binding site, and transcription of the lac operon is turned off.
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