Hi in this video, we're going to be talking about enzyme kinetics. So what our enzyme kinetics will they actually enzyme kinetics is actually measuring the activity of an enzyme. So, um this actually refers to measuring the relationship between the substrate concentration and the speed of enzyme reaction. So, because it depends on the concentrations of the substrate I've prepared for you to different um potential ways reactions can occur. So the first is that there's low substrate concentration. That means there's going to be less collisions and that for the substrate is rate limiting. So if we look at this example here, let me back out of the way. You can see that if there's a low amount of substrate. So here there's a ton of enzymes that there's going to be really just only a few collisions between substrate and enzyme. And therefore we say the substrate is right limiting. Which means that the substrate is controlling the rate of the reaction. Now, if we go to the second um potential occurrence and that is there's the high substrate concentration, then there's more collision between enzymes and substrates and the enzyme is rate limiting. So this is actually over here. So you can see there's a ton of substrates. Um so there's a high substrate concentration. So there's more collision. And that means that the enzyme is right limiting because all of the enzymes are bound and so there there can't be, you know, it can only go as fast as there are enzymes to catalyze the reaction. And so enzyme kinetics really deals with looking at these two different reactions. You know, how much substrate, how much enzyme is there, So how fast can the reaction occur? And so generally, enzyme kinetics is a measure that is measured before any product has been formed. And so that way we can actually look and see, you know, how fast is the reaction going to occur before it actually gets started? So now let's move on.
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So how do we measure enzyme kinetics? Well, we do this through these two values here. The V. Max and the K. M. And the K. M. Is also called the Michaelis constant. You'll see the minton Michaelis equation maybe come up in your textbook and so this is this is what we're talking about here and this. These two measures are the measure of enzyme performance. So what do each of the measure? Well, the V. Max measures the velocity or the speed of the enzyme reaction. So this depends on the substrate concentration obviously. So as the substrate concentration gets higher and becomes more saturated um This is when um the upper level of reactivity is um is met. So again, high substrate concentrations, more collision between enzyme and substrate enzyme is rate limiting. So at these situations when the substrate concentration is saturated, that is when you want to measure the max because that's going to be the fastest way the reaction occurs if we have so many substrates, all of the enzymes are failed until they're acting maximally to speed up the reaction as fast as possible. Now this is different from the K. M. Which actually measures enzyme function by determining the concentration of subs tract needed to work at half the max. So depending on what half the max is the K. M. Actually measures how tightly um the enzyme and substrate are bound. So a small K. M. Is going to bind tightly where a large K. M. The enzyme binds weakly. And these can also these values can be used to calculate what's known as the turnover number which is how rapidly a substrate molecule can undergo a reaction. So now let's look at these relationships via actual image, which I think becomes easier to conceptualize this. So on the Y axis we actually have reaction velocity speed. So this is obviously this is occurring faster and then we have a substrate concentration which again is increasing on the X. Axis. So we have the max here we have half the max and V. Max. And the max is going to be the speed of the reaction when the substrate is saturated. So all the enzymes have substrate bound to them and there's an excessive substrate. So how fast can the reaction occur? Which here is going to be this number. Now the K. M. Is looking at what is the amount of substrate bound at half the max. So half the max is here at this this point here and so how much substrate is bound? We follow the line and we go down so the amount of substrate bound is here. So amount sub straight bound at one half B max. Now remember I said that you can use the K. M. Value to determine how tightly the enzyme is binding. Well we can do this because if the half the max is fairly low then we know or the concentration of the substrate needed um to create half the max is is fairly low and we know that enzyme is working very well. It's sort of binding tightly doing its thing and releasing it binding tightly doing its thing. So it's happening quickly. Whereas if the concentration is really high, say here for instance and have the max is here, then we can say, okay, well the enzyme is actually binding fairly loosely and it's not being very efficient at what it's doing and therefore um you know, it's it's not efficient, it's binding loosely. And so the substrate concentration needed to make half the max is actually really high. Um And so that's the relationship between v max K. M. And the concentration of substrates. So now let's move on.
If an enzyme is determined to have a low Km what does that say about the reaction?
The enzyme binds loosely to the substrate
That the speed of the reaction is slow
The enzyme binds tightly to the substrate
That the speed of the reaction is fast
Which of the following terms describes how rapidly a substrate can undergo a reaction?