Enzyme Kinetics

in this video, we're going to begin our discussions on enzyme kinetics, so enzyme kinetics is just the branch of biochemistry that's related to the rate or the velocity of an enzyme catalyzed reaction. And so, of course, it's going to be measured by the reaction rate or the reaction velocity, which we refresh our memories on in our last lesson video. So we know that it symbolized with lower case letter V, and so enzyme kinetics actually has a lot of different factors that are incorporated into it. And so moving forward and our next couple of videos, we're going to slowly introduce the most important factors when it comes toe enzyme kinetics that you guys need to be familiar with. And we're going to start with how to increase the reaction rates that effect enzyme kinetics. And so, in general, there are three ways to increase the rate of a reaction, and the first way is to increase the temperature of the system. Now, this method actually provides an issue to cells because increasing the temperature can non specifically increase all of the reaction rates in the system. And that is typically not what sells want to dio typically sells, want toe, have control over exactly what reaction is going to increase the reaction rate. And if you increase the temperature too much, that could eventually lead to the D nature ation of proteins. And so if we take a look at our first method down below in our example, notice that we have ah, graph that has the reaction rate on the Y axis and the temperature on the X axis and notice that in the beginning, as the temperature increases, so does the reaction rate. But again, the reaction rate of all of the reactions and the systems are going to increase, not just the very particular reaction that a cell might be interested in increasing. Now, the reaction rate will Onley increase up to a point where proteins in the cell begin to the nature and once proteins in the cell begin to the nature, the cell is going to become stressed and eventually die. And so over time the reaction rate is going to plummet and decrease. And so, for that reason, this first method increasing the temperature is not the go to method that sells, uh, typically use thio, increase their reaction rates now, the second main way to increase the rate of a reaction is to increase the substrate concentration. Now, this method also provides an issue for cells because increasing the substrate concentration takes lots of time and energy in order to make enough substrate that will actually increase the reaction rate enough. And so when we make so much substrate that could potentially create overcrowding and the already limited space within the cellular environment. And so if we take a look at our second method down below, in our example, notice we have a graph again that has the reaction rate on the Y axis. But this time we have the substrate concentration on the X axis and notice that as the substrate concentration increases, so does the reaction rate. But notice that in order to get the reaction rate up to a point that significantly high enough, we would have to add so much substrate where the essentially the amount of substrate is going to go off of the graph and that is a lot of substrate. If we were toe, add this much substrate that could create overcrowding within the cell. And so, for these reasons, this is not the typical go to method for how cells increase their reaction rates. So moving on to our third method that increases reaction rates, uh, you can add a catalyst to the reaction. And so this method here actually provides a solution for cells on how to increase their reaction rates, because living systems on Lee need to use very small amounts of enzymes in order to increase their reaction rates. And so if we take a look at our third method down below, in our example, notice we have a graph again that has the reaction rate on the Y axis and again, the substrate concentration on the X axis. So we have the same curve over here for the UN catalyzed reaction that we had before. And so the point here is that when we add an enzyme, so this red curve represents the enzyme catalyzed reaction noticed that with lower concentrations of substrate were able to get much higher reaction rates. And so just by adding small amounts of an enzyme, were able to increase the reaction rates drastically. And that's why uh, utilizing enzymes is the go to method for cells and living systems to increase their reaction rates. And so moving forward, we're gonna be able to get some practice utilizing these concepts, so I'll see you guys in those videos.

So in our last lesson video, we said that enzyme kinetics is measured by the reaction rate or the speed of a reaction. And we also said that there are many factors or variables to consider when it comes to enzyme kinetics. And so, in this video we're going to introduce all of the enzyme kinetics variables and notice down below. In our example, we have all of these enzyme kinetics variables, and that's a lot to remember. But don't worry, because moving forward in our course, we're going to slowly break down each one of these new enzyme kinetic variables one by one, so that you guys can better understand how they relate toe enzyme kinetics and so getting started here. What I want you guys to first recognize is that the first four enzyme kinetics variables are review from our previous lesson videos. And so not all of these variables are new information. Some of it is review information. And so we already know that the e stands for enzyme, and we also already know that brackets means the concentration. And so this symbol here is the concentration of free enzyme molecules. Now we also know that s is for substrate, and so this symbol represents the concentration of free substrate molecules. E S is, of course, going to be the enzyme substrate complex. And so this is going to be the concentration of the enzyme substrate complex. And then last but not least, here. P, we already know, stands for the product, and so the symbol is going to be the concentration of free product molecules. And so again, this is almost half of our table vertically, so that is a good sign that it's all review, and there's not that much new information here. But our first new variable is this variable right here, which has the letters e and t in it. So what could this possibly represent? I can tell you it's not e t phone home, so what could it be? That's right. So it's going to be the total. It's going to be the total amount of enzyme, the total concentration of enzyme. So the tea here is for total. And so what this means is it's going to include both the enzyme that is free that is not bound to the substrate, and it's also going to include the enzyme that is bound to the substrate in the enzyme substrate complex. And so the sum of both of these variables that we already covered up above is going to be the this new variable right here. So it's pretty easy and straightforward and really, this one here doesn't take ah lot of, uh, memory effort. It's pretty simple. Just remember, the tea is for Total. So really, here we have these variables that are new and again these are gonna be the ones that moving forward in our course. We're going to break down one by one so that we can better understand how they work and connect to enzyme kinetics. And so the first one that we're going to talk about here is this lower case K here, which stands for the rate constant. The next one that we have here is this K with a little M, which stands for the Michaelis content constant. And then this one over here that we have is K cat and the cat stands for not a kitty cat, but the catalytic constant and again moving forward in our course. We're gonna talk about each one of these variables. Now, over here on this side. We already know that V is, uh, the variable for the reaction rate. And so these v s here are also for the reaction rate or the reaction velocities. And so what makes them different is the little sub scripts that they have. So this one has a zero, and that's termed V not. And so this is going to be the initial reaction velocity at the very, very beginning of a reaction. And then this one here, which is V Max, is, of course, going to be the maximum reaction velocity. And so this introduces and defines or introduces all of the enzyme kinetic variables and again, moving forward in our course, we're gonna be breaking each one of these down, starting with the rate constant. So I'll see you guys in our next lesson video where we'll cover that variable.

So before we actually talk about the rate constant variable in our next topic, I first want to point out something that's really important to note about when biochemists are trying to study enzymes in a laboratory. And so this video might get a little bit confusing for you guys. But that's okay, because there's only one thing that I want you guys to take away from this video. And so not only are we gonna cover that one thing throughout the video, but by the end of the video I'll do a quick recap to make sure you guys know exactly what that one thing is that I want you to take away from this video. And so that being said, Let's go on and get started. So first I want you guys to recall from our previous lesson video that we define the total enzyme concentration, or E T. As the some of the free enzyme concentration, plus the concentration of enzyme that's present in the enzyme substrate complex. And so we distinguished the total enzyme concentration from the free enzyme concentration. And we did that because we have this enzyme substrate complex that forms now, however, do We also need to consider the same for the substrate. Do we need to consider that the total substrate concentration is equal to the sum of the free substrate concentration, plus the concentration of substrate in the enzyme substrate complex? Well, it turns out that even though we know that enzyme kinetics is affected by both the total enzyme concentration and the total substrate concentration the answer to this question up above do we need to consider this expression is no. We do not need to consider this expression right here. And so that means that we do not need to define the total enzyme concentration as a separate variable from the free enzyme concentration. And that's exactly why, in our last lesson video, we did not include the total substrate concentration. Now, why is it exactly that we don't need to consider this expression right here? Well, the answer turns out to be that under typical laboratory conditions, when we're studying enzymes in a lab, the total substrate concentration is in great access over the total enzyme concentration. So there's much, much more substrate than there is enzyme. And so we can say that the total substrate concentration is going to be much, much, much greater than the total enzyme concentration. And so what this means is that the amount of substrate that's going to be bound to the enzyme substrate complex at any given time throughout the reaction is going to be pretty much negligible in comparison to the total substrate concentration. And so what this means is that if the substrate concentration that's bound to the enzyme substrate, constant concentration is negligible. This means that the enzyme substrate concentration is going to be super, super, super small in comparison to the total substrate concentration. Which means that in this expression right here, we can pretty much eliminate this entire, uh, concentration. And so what that means is we can say that the total substrate concentration is going to be equal to the free substrate concentration. And so that's exactly what we're saying. Over here, the total substrate concentration is equal to the free substrate concentration and so down below, we're saying the same exact thing. We're saying that the total substrate concentration can really be expressed as the free substrate concentration. So they're pretty much the same exact thing, which is why we didn't define this variable uh, here in our last lesson video. And the reason that this portion right here is true is because again, the substrate concentration is always so much greater than the total enzyme concentration, Which means that the substrate concentration will also be much greater than the concentration of the enzyme substrate complex and so down below. What we have is a little graph to help remind you guys that the substrate concentration right here in blue is going to be much, much greater notice. It's much greater than the enzyme concentration here in red. And so we can say that the total enzyme concentration remains small and relatively stable in, uh, under laboratory conditions. And so notice here that we have a star and this star here is going to come back up later in our course when we're talking about meticulous meant in enzyme kinetics and the assumptions of McHale is meant an enzyme kinetics. But again, we're not going to talk about that until a little bit later in our course. But for now, what I want you guys to know is that this star here is going to represent something later in our courts, so keep that in mind. And so like I said, there's only one thing that I really want you guys to take away from this video and that is the conclusion here. And so moving forward in our course, we're going to say that the substrate concentration, the free substrate concentration is actually going to represent the total amount of substrate. And so again, uh, that's pretty much exactly what we've been saying is that the substrate concentration, the free substrate concentration is about equal to the total substrate concentration. And so you're not going to see us use this variable moving forward. You'll Onley see us using this variable. And that is the Onley. Take away that I want you guys to take from this video. So that concludes this video and I'll see you guys in our next one