So now that we've covered Alice Terek defectors in this video, we're going to introduce the first model that explains positive cooperative ity and the sigmoid all kinetics of Alice Derek Enzymes. And that first model is the concerted model. And so the concerted model is also sometimes referred to as just the MWC model. And MWC is just the abbreviations of the last names of the three scientists that discovered the concerted model. But what I found is that this model is more commonly referred to as just the concerted model than the MWC model, and so moving forward in our course I'm or commonly going to be referring to. It is just the concerted model. And so recall from your previous organic chemistry course is that the word concerted just means jointly happening all together at the same exact time. So concerted really just means simultaneous. And so the concerted model is just suggesting that there are simultaneous T state to our state conversions in all of the sub units of analysis, Eric Enzyme And so, in other words, the concerted models just saying that the T state tow our state conversions encompasses the entire Alice Derek enzyme as a whole, so that all of the sub units are simultaneously converting from the T state to the our state and vice versa. And so this ties directly into what's known as the symmetry role. And so the cemetery role just says that all of the sub units of analysis Eric Enzyme, must always be in the same confirmation or state. And so this means that all of the sub units of analysis Eric Enzyme, must either be in the T state or all of the sub units of analysis. Eric Enzyme must be in the our state, but there are absolutely no hybrids allowed. And so, looking at our image down below, over here on the left hand side, what we have is an Alice Terek enzyme with four different subunits. And so notice that all four of these subunits of the Alistair enzyme are all in the same exact state. They're all in the T state, and that is part of the symmetry role here. And so notice that no matter how we cut this Alice Derek enzyme in half, if we cut it in half this way, or if we cut it in half this way we're going to have perfect symmetry. And so notice down below. Here these green circles represent the Alice Derek enzyme with all four sub units in the free our state and again, all of the sub units of analysis. Eric Enzyme, when it comes to the concerted model, must always be in the same state. So they must always be in the T state, or they must always be in the our state. And again, absolutely no hybrids are allowed. And so over here on the right hand side, what we're emphasizing is that same idea. So the concerted model we know is also referred to a zoo, the MWC model at times. And so when the Alice Derek Enzyme converts from the T state to the our state, the conversions encompass the entire enzyme as a whole, so that all four of its sub units are gonna convert simultaneously. And so the all of the sub units of analysis Eric Enzyme, are always going to be in the same exact state. And so what's also important to note about the concerted model is that absolutely no substrate is needed or required to induce the fit and induce the conversion of the Alistair enzyme from the T state to the our state. Which means that the Alice Derek Enzyme is able to convert from the T state, toothy our state even in the absence of substrate. So even when no substrate is present and instead what controls the conversion of the enzyme from the T state to the our state and vice versa is just a natural equilibrium that exists between the two states allowing for them to convert between the two states. And so what's important to note is that even though we mentioned up above that, no substrate is needed to induce this conversion. And so though no substrate is required to induce this t state, our state conversion, the changing of the substrate essentially increasing the substrate concentration is going to affect this t state tow our state equilibrium. And so this T state to our state equilibrium is actually going to be shifted when we increase the substrate concentration as we'll see in our next lesson video. And so when we increase the substrate concentration, this T state to our state equilibrium is shifted towards the our state, allowing the Alice Derek enzyme toe bind mawr substrate easier and therefore allowing for positive cooperative ity. But again, we're going to talk more about this idea in our next lesson. Video for now, down below. In this portion of our image notice it's reminding us that absolutely no substrate is needed or required for the Alice Derek enzyme to convert from the T state to the our state or vice versa. And essentially, because all of the sub units are always going to be in the same state in the concerted model. Uh, no. Hybrids are allowed whatsoever. And so we can't have within the same Alice Derek enzyme one sub unit in our state, whereas the other sub units are in the T state and we can't have any combination of, uh, t state In our state sub units, all of the sub units must either be in the T state or all of the sub units must be in the our state. And so these are the fundamentals to understanding the concerted MWC model and our next lesson video. We're going to talk about how the concerted model allows for positive cooperative ity and the sigmoid all kinetics of Alice Derek Enzyme. So I'll see you guys in that video

So in our last lesson video, we explain the basics of the concerted model. And so in this video, we're going to talk about how the concerted model allows for positive cooperative ity and therefore explains the sigmoid all kinetics of Alice Derek Enzymes. And so, recall from our previous lesson videos, we have defined positive cooperative ity. And so we have somewhat of an idea that positive cooperative ITI is just this idea that the binding of a substrate molecule to the Alice Derek enzyme can disrupt the t state, our state equilibrium in favor of the our state to essentially increase the initial reaction velocity or the V not of the enzyme catalyzed reaction. And so it's this positive cooperative ity that accounts for the sharp increase that we see with the initial reaction velocity in the sigmoid all kinetics curve of Alice Terek enzymes. And so, if we take a look at our enzyme kinetics plot down below in our image, notice that we have our sigmoid all curve right here for the Alice Derek Enzyme. And so we're also indicating positive cooperative ity right here and positive cooperative ITI is really what explains this sharp increase that we see in the initial reaction velocity. Uh, here at this stage right here how it increases so sharply is explained by positive cooperative ity. And so again, the concerted model allows for positive cooperative ity. And so, in order to understand how the concerted model allows for positive cooperative ity, what we need to do is recall from our previous lesson videos that when there is no substrate concentration essentially at very, very low substrate concentrations, the equilibrium of the T state and the our state actually favors the inactive T state. And so if the T state is favored, of course, that means that the T State is going to be in a high concentration at these low substrate concentrations. And so if there's a high concentration of t state, then that means that the Alice Derek Constant l not eyes going to have a high concentration of t state and therefore be very large. And so there will be in large Alistair constant l not at low substrate concentrations. And so under cellular conditions, even when there is low substrate concentrations, it's important to know that the Alice Derek Enzyme can still sometimes spontaneously convert from the T State, which is going to be again in high abundance, uh, to the our state. Which means that even at these low substrate concentrations, even when there's no substrate present, they're still going to be some small percentage of the Alice Derek enzyme in the our state, even though most of the Alice Derek enzymes will be in the T state. And so if we take a look at our image down below to apply some of these concepts notice, uh, down below. Here, we're showing you guys, uh, the concerted or the MWC model. And so notice over here we have a little key. And so, uh, these pink squares again represent the Alice Terek enzyme with for sub units all in the T state. And then, of course, here what we have is the Alice Derek enzyme with four sub units, all in the free our state. And of course, we know that the our state is going to bind substrate more efficiently. And so, uh, these individual sub units are capable of binding substrate. So these yellow circles here represents the sub units with substrate bound, and so this would be the Alice Derek enzyme with one sub unit binding substrate. This one has to sub units binding substrate, three sub units, binding substrate. And then this one down here is the Alice Terek enzyme with all four subunits binding substrate. And so notice that again at very, very low substrate concentrations essentially, when the substrate concentration is equal to zero, uh, the equilibrium is going to favor the T state. And so that's why we have most of the Alice Derek enzymes here present in the T State. And we have still a small percentage of the Alice Derek enzyme in the free our state when there's no substrate present. And so if we go back up to our text up above. What's important to note is that as we start to increase the substrate concentrations to hire substrate concentrations essentially increasing from the low substrate concentrations to hire substrate concentrations, it becomes mawr likely that the substrate molecules are going to bind to an our state sub unit. And as soon as a substrate molecule binds toe one our state sub unit, it's going to trap all of the other sub units of the Alice Derek enzyme in the our state as well And so if we go down low notice that, uh, here we have zero substrate. But as we slightly start to increase the substrate concentration, notice that some of these, um uh, sub units here, like this one right here will bind to a substrate. And once one sub unit binds to a substrate, it traps the other sub units and the our state as well, making them more likely toe bind, substrate. And so that's exactly what we're seeing over here. Notice that we have one sub unit that bound substrate. And this will trap the other three sub units here in the our state as well, making them more likely to bind substrate. And so this is exactly what we mean by positive cooperative ity. The binding of one substrate molecule essentially leads to making it a lot easier for other substrates, uh, for other enzymes to bind substrate. And so, as we start to increase the substrate concentration even higher, so higher substrate concentration is going to lead to even mawr substrate binding. And essentially, it's going to lead to the trapping of, uh, Alice Derek enzyme sub units in the our state. And of course, if the enzyme is being trapped in the our state. That's going to increase the concentration of our state. And an increase in the concentration of the our state is going to decrease the Alistair constant. And so that's why we get a lower Alice, Derek Constant. But because we have mawr enzymes in the our state binding substrate, that ultimately leads to an increase in the initial reaction velocity. And that is essentially what explains this sharp increase that we see here that is all, uh, related to the positive cooperative ity. And so notice that as we move to the right on the scale here that the substrate concentration is increasing. And as we increase the substrate concentration, we start to get mawr and Mawr of the our state enzymes. And we also start to get mawr and Mawr of the our state enzymes binding thio substrates. And so we start to see mawr yellow as we move to the right so you can see we start to get a lot more yellow, Uh, as we increase the substrate concentration And when we get more yellow, of course, that means that we have Mawr enzyme substrate complex and that means that we're going to have a higher reaction velocity. And that explains this sharp increase in the reaction velocity. And so notice that at this point, right here on our curve, this is exactly where half or half here of all of the active sites are going to be occupied with substrate. And so when the initial reaction velocity approaches the V Max, that means that all of the present enzymes are going to be bound with substrate. Essentially, all of them will look like, uh, this with all yellow at this point up here where it approaches V Max. And so this year concludes our lesson on how the concerted model can explain positive cooperative ity and therefore explain the sigmoid all kinetics of Alice Terek enzymes. And and our next lesson video will be able to talk about the other model That explains positive cooperative ity as well. And that is the sequential model. So I'll see you guys in our next video