Lac Operon

Hi in this video we're gonna be talking about the lack opteron. So an opera Ron is defined as a group of genes that have a similar function and they're transcribed together. Now remember we're talking about pro carry Odjick gene regulation, that's what that operation is always pro carry ah tick. So you find a bunch of different types of opera ions in the pro carry optic genome and we're gonna talk about many of them. But the first one we're gonna talk about is a lack opera on and that's because it was discovered first now to understand an opera and we have to understand its components and so there are many different components in an opera on. And the short term way to remember this is Prague. So the P in Prague stands for a promoter and this and we've talked about promoters before when we talked about transcription. And so it's the same thing promoter is the region where a transcription initiator binds and this starts transcription. So operations have promoters. They also have a repressor. This is the R. And Prague and this is actually a protein that represses transcription of the opteron and it does this by binding to the O. Region of Prague called an operator. So the operator is where the repressor binds and this is an on off switch. So if the repressor is bound, transcription is not going to happen because it's being repressed. But if the repressor is not bound and the operator is open then that means transcription can occur. So the operator really determines is this happening or not. And then finally the G. In Prague stands for jeans. And these are the genes that are transcribed together. So if we look at a typical opera on here. So here's the lack opera in these boxes. You can see there's a promoter or a transcription initiators will bind. There's an operator whether oppressor will bind. You have your genes here, which there's three like Z. Y and A. And then there's actually a thing over here that's not in Prague but it's called the terminator. And it's found in a lot of ah perons and it obviously will terminate the transcription of the Oberon. So let's talk about the lack opera. And like I said, it was the first opera and discovered it was discovered by these two scientists. It's their French names, vehicle. And you know, I don't know, I'm not French, I don't speak French. But if you do you can pronounce those right? And it was found in the 1960s. And so the lack opera and encodes a group of genes that break down and process lactose. Now, if you remember what lactose is right? It's a sugar. Um And the sugar has to be broken down by the pro cryonics cell so that it can use it for energy. And so the lack opteron is in charge of taking that lactose and chopping it down into its little pieces so that it has that so it can use that energy. And what it breaks it down into is actually encoded by the Black sea region. This encodes beta galactic days and that chops down the lactose into glucose and galactose and glucose is really what's used by the cell for energy. So this is what it really wants when it breaks down that lactose. But there's other genes and they're super also important for making sure that lactose can be digested. The lack Y and coats. A gene called permeate. And this allows lactose to enter into the south side of lactose couldn't get in. It couldn't be broken down, could not be used for energy. So permeates is super important. And then we have like a and this occurred. This encodes a transit see delays and actually most people don't really know what this function is. But without it lactose doesn't get digested correctly. So it is crucial for this lactose processing even if it's not understood exactly what it does. So here's this um opera. And again remember we have a promoter opera on and then we have Z. Which is in charge of breaking it down breakdown beta galactic days. We have lack Y which is a responsible for making sure that lactose lactose can enter and then we have like a which is, it's kind of unknown but it does have an important function and it is required for transcription of this opera on. So that is the overview of the black Albarran. Now let's turn the page

Okay, so now let's talk about lack opteron regulation. Right? This is a chapter on gene regulation. So um let's we're gonna spend the majority of this time talking about how pro periodic jeans like the lack Oberon are regulated. So the lack opera remember it digests lactose, that's its function um is to encode those genes that do that and so it responds differently or it's regulated differently depending on the lactose concentration. So if lactose there's a very high lactose concentration, what happens is lactose will actually bind to a repressor. And when lactose is bound to that repressor it, the repressor is then removed from the operator. So remember Prague are as the repressor and o is the operator and normally in the lac opteron the repressor is bound to the operator and that completely stops transcription of those jeans. But when lactose concentration is high, that means that the cell needs those genes in order to break it down. So lactose binds repressor is removed from the operator and that means transcription of the operator can or the operation can take place. So that means the lack operation jeans are made and then they act to break down lactose. Now if lactose lactose concentration is low, that means it doesn't bind to the repressor so it stays on the operator and it continues to repress transcription and so transcription does not take place. So if we look here, we'll say that this is the lack opteron right? You have 123 and this here is gonna be the repressor. So you can see if there is low lactose, there's really nothing over here around it's gonna remain bound and transcription will not take place if the lactose concentration is high. So here is lactose. See there's a ton of it around. It will then bind to the repressor. That repressor will be removed from the operator and then transcription will take place. So that is how the lack Oberon responds to lactose. Now that you probably have heard this before in another biology class. This is a very common example that's used but now we're going to take it a step further. And the fact is the lack opteron, even though it digests lactose, it's actually sensitive to glucose concentrations as well. So the lactose we talked about how it's sensitive to lactose concentrations and that's completely independent of what we're about to say. So the lack opteron responds to glucose and how it does this is through a protein called the metabolite activator protein or cap for sure. And this is a protein that represses lack opteron when glucose is present. So this is another type of repressor protein. And so how this works. So this is kind of the summary, right? The cap. It's a protein. It's a repressor. It will repress opera on glucose is present. So that is the summary, right? Like that's what you need to know if glucose is present. It will repress it. But let me explain how and it gets a little detailed with a lot of new book cab for it. So we're going to take it slow. So when glucose is in the south, so there's a high amount of glucose it's actually going to inhibit the activity of this protein called edina cyclists. And what a dino cycle is does is it creates another molecule called Camp C. A. M. P. So when glucose is present that means there's going to be low amounts of C A. M. P. Now if if the C A. P concentration is high, it binds the cap. If it's low it doesn't bind the cap. So we have this cap protein and C A. M. P. Can come in and bind but it's only going to do it. If it's present. And remember if glucose is present then the C. A. M. P concentration will be very low. So if glucose is present, C A M. P. Is not gonna bind. But if there's a low amount of glucose it will bind. Now. What happens when this, what does this do? The cap bound to the C. A. M. P. So this complex will bind to a specific site called the cap site and its upstream of the promoter. So remember we said Prague this binding site is actually here. It's up sharing and it's not present in every operation but it is present in this one. So this protein here, this complex, the cap and the C A. M. P. Will bind here to this cap site and activate and it'll activate transcription. So this means that if glucose is high it inhibits C A. M. P and represses transcription, it doesn't activate it. When glucose is low there will be high amounts of C A M. P. High amounts of this and activates transcription. So this is here the summary. So if you ever get confused on how this is working, this is this is the summary. So there's a lot of glucose around. There's not a lot of C A. M. P. And no transcription occurs. So that means it will repress when glucose is present, right? Which is what we said above. But if glucose isn't present low concentration there's gonna be a lot of C. A. M. P. Which means it will bind to C. A. P. Create this molecule which will bind here. And when it's bound it activates transcription. So let's look at what this looks like. Let me disappear for a second. So here we have our opteron. We have a promoter or operator. Um there's a repressor here but it's not shown because we're not talking about that now this is gonna be the lactose repressor. Um And then you have your genes we have Prague right? But we also have this extra special region here which right here's the cap binding site. So in a situation of low glucose and lactose is available. What happens is because the lactose is available. The lactose repressor allows transcription. But the low glucose means that C a m p will be produced. It will bind to the cat protein that will be recruited to this region upstream of the promoter, and that means that these genes will be strongly expressed. Transcription will happen because of the lactose and also because of the glucose. So the lack opera can be regulated by lactose and glucose, but it does so through two completely different ways. Lactose is through the repressor and glucose is through the cap N c a m P complex. So with that, let's not turn the page.

Okay. So now let's talk about the summary of the lack operation expression. So in regulation right? Because now we understand well, we know how the lack operations regulated with lactose, we know how it's regulated with glucose. But in the cell that you don't just have one or the other, you have combinations. You can have high lactose and low glucose or high glucose and low lactose. And let's talk about how the lack opteron responds differently to different concentrations of glucose and lactose. So if but you need to know some things first. So if glucose and lactose are both present and high levels in the cell, the cell is going to utilize glucose first. And the reason is because it's simpler, it doesn't need to be broken down, it doesn't need all these genes so that glucose is going to be used first. But if you only have lactose and you don't have glucose, that means that the cell has to break down the lactose to generate the glucose. So with that let's talk about the different concentrations. So let's first focus on lactose because that's what we talked about first, the lactose repressor. So remember if lactose is high, that's going to bind to that repressor, remove it from the operator and allowed transcription. And so anytime that the lactose is high transcription can occur because the repressor has moved and that transcription will occur. But alternatively, if lactose concentration is low, that means that repressor is going to be on it. So under here, you have the repressor bound and if that repressor is bound, there's going to be no transcription taking place. So whether or not glucose is present in the cell or not. If you have low levels of lactose that repressor is going to be bound and there's gonna be no transcription. So what we have to focus on is high levels of lactose and then compare that between high levels of glucose and low levels of glucose. So lactose. Well if we're we have to look at that first because if lactose concentration is low no transcription is gonna take place. So what happens if lactose concentration is high and glucose concentration is different? So like I said if lactose concentration is low it doesn't matter whether glucose is high or it's low it's still not going to be expressed because the lactose repressor is going to repress it. So these we don't even have to worry about, we've already talked about these but these two are the ones that are going to focus on. So if lactose concentration is high and glucose concentration is low we know that the repressor is not gonna be bound for lactose. So the transcription will take place. But when we talk about glucose we have to refer to the cap approaching now remember if glucose concentration is low you're gonna have cap and it's going to be bound to C. A. M. P. And that is going to buy an upstream of Prague and I go here and that's going to activate it as well. So now you have the lactose concentration, the high lactose concentration activating it and you also have a low glucose concentration and that activates it more. So these are gonna be very strongly expressed. So it's not that they're just being expressed. You actually have both of these conditions activating that transcription. And so it's gonna be almost double activated. It's gonna be super activated. Whereas if you have high concentrations of lactose and high concentrations of glucose, what you get is you get the lactose is still activating this but the glucose isn't right because the cat protein doesn't have any C. A. M. P. On it meaning that it will not bind here and will not activate. So you still get expression right because the lactose is still um causing this expression but it's not going to be strongly expressed because you're only getting one sort of push of transcription and not to. Um So these are the this is kind of your summary table. You can look at it without all my riding on it and understand that if lactose concentration is high um and glucose is low it's gonna be strongly expressed. But if lactose is high and glucose is high it's only gonna be somewhat expressed and the reason is because the cell already has a bunch of glucose so it doesn't need to break down more lactose to get more glucose. There's already a ton of it present. So these opera isn't as needed as it would be if the cell didn't have a lot of glucose. And so that's the reason the difference between the two. But either way if lactose concentration is low then it's not going to be expressed because that repressed er will be found. So let's look at this. So here we have our lack opteron we have our Prague um we have our cat binding site and let's look at the different concentration or how the different concentrations affect this. Um What am I trying to say this operation? So if lactose is available does that mean the repressor is going to be there or it's not? Right lactose is gonna bind the repressor. So there's gonna be no repressor so that's gonna activate. And if there's low glucose that means that the cat protein is gonna be bound to the C. A. M. P. It's gonna bind. And that binding is going to also activate. So you're gonna get strong expression If you have low glucose and low lactose that means that the repressor will be bound. Right? And you have low glucose. So that means that's also not going to activate it because you have your C. A. M. P. But no cap. Right? And so you have your oppressor here. So when that repressor is bound, you're gonna have no expression. And so if you have lactose available and high glucose what you get is you get the repressor is removed. So you have no repressor you have activation. But when high glucose that means that the c. The cat approaching will not be bound to the C a. M. P. With no binding. So this binding site here is left open and that means there's gonna be no activation. So no activation and that means that it will be expressed. There's a low basal level of expression but you don't get this strong expression that you would if you had this combination of low glucose and lactose available. Um So that is the summary of the lac opteron and how glucose and lactose concentrations affect the expression of this. These pro carry arctic operations in the case of the lac opteron. So with that let's now move on.