1

concept

## Michaelis-Menten Assumptions

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alright. So, up until this point, in our course, we've Onley briefly mentioned in some of our previous lesson videos. McHale is meant in McHale is meant in Kinetics or McHale is meant in equation. And so in this video, we're finally going to talk directly about Makayla Cement in. And so we're going to introduce Makayla Cement in and begin. Our discussion on the McHale is meant in enzyme kinetics assumptions. And so Michaela cementing are actually the last names of people they were actually ends, um, ologists or scientists that study enzymes. And so Michaelis was actually the last name of a German man named Leah, Norma Kayla's and so down below we can see we have an image of Leonora McHale is, and we could see he was a pretty sharp eye with this perfectly groomed mustache and thes, super stylish antique glasses, and so meant in was actually the last name of the Canadian woman named Maude Minton. And so you can see down below, we have an image of Maud Minton. And so Michalis and mention actually proposed a fundamental model to explain enzyme kinetics way, way back in 1913. And so really, what Makayla Cement and proposed was that during an enzyme catalyzed reaction, they suggested that it is necessary for an enzyme substrate complex toe form during the reaction. And so before Maude Minton and Leonora McAleese's model fundamental model. Some people believe that enzymes would speed up chemical reactions by secrete ing some kind of chemical to speed up the reaction So we can see here how Mikhail's and maintenance model was incredibly important to enzyme kinetics and so recall That meant Maude Minton was a Canadian woman. And her accomplishments and her, um, contributions to enzyme kinetics are incredibly impressive, especially considering the fact that way back in the hundreds during her time in Canada, the Canadian law actually did not give woman the right to vote. And even though it was a controversial, some people believe that the language that was included in the Canadian law suggested that on Lee a man could be a person. And so technically, we could say that, uh, the Canadian law said that woman were not even considered people. And so that's why it's so incredibly impressive that Maude Minton was able to not only become a medical doctor but also get her PhD and contribute so much toe enzyme kinetics. And so what you'll notice here is that below. What we have is the meticulous meant in equation. However, this is not the main focus of this video, and we're going to talk more about the meticulous meant an equation later in our course. But for now, all I want you guys to know is that the meticulous meant an enzyme kinetics model or equation. Will Onley work under a few simple assumptions? And so, in our next lesson video, before we actually dive into detail on the meticulous meant in equation, we're actually going to talk about these particular assumptions that are needed for this meticulous meant an equation toe work. And so again, we'll talk about this. McHale is meant an equation later and our course. And so that concludes. Our introduction to McHale is and mention, and the McHale is meant in enzyme kinetics assumptions, and I'll see you guys in our next video, where we'll talk about these assumptions in more detail.

2

concept

## Michaelis-Menten Assumptions

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So in our last lesson video, we said that the McHale is meant in equation, which we're going to talk more about later. In our course, Onley works under a few simple assumptions. And so those assumptions can actually be condensed down into really three Michaelis Menton assumptions. And so again, the McHale is meant. An equation that we'll talk about later in our course is Onley derived under these following three assumptions and so notice that we've labeled are three assumptions with these three stars. And so these stars should look kind of familiar to you guys. And so do you guys remember and some of our previous lesson videos We had these stars and I said, Remember these stars because we're going to talk about them mawr later in our course. Well, this is that video where we're going to talk about all three of those stars from our previous lesson video. And so the best part about this video and these three assumptions is that we've already covered all three of these assumptions in our previous lesson videos. And so really, there's no new information in this video. And so our first start here, or our first assumption is the substrate concentration assumption, and that basically says to assume that the total substrate concentration is approximately equal to the free substrate concentration. And so in the McHale is meant in equation. We can use the free substrate concentration symbol to represent the total substrate concentration and so recall from our previous lesson videos. The reason that this is true is because the free substrate concentration is so much greater than the total enzyme concentration, which means that the concentration of the enzyme substrate complex is negligible in comparison to the free substrate concentration. And so, if we noticed that the star number one, we have an image for star number one and it's the same image that we use in our previous lesson, Dio. So we already know that the substrate concentration is going to be much, much, much greater than the enzyme concentration. And because that's true, we can say that this symbol here, the free substrate concentration can be used to represent the total substrate concentration so moving forward, we're on Lee going to see this symbol being used in our McHale is meant an equation, and that's all this first assumption is saying now. moving on to our second star or our second assumption. It is the initial velocity assumption. And so the initial velocity assumption says that we're on Lee going toe focus on measuring the initial velocity of an enzyme catalyzed reaction. And we already knew that, right? Biochemists like to focus on the initial velocity of an enzyme catalyzed reaction, and that is because the reverse reaction from, uh, product backwards into the enzyme substrate complex or essentially the rate constant K minus two is essentially negligible, really early on in the reaction since, um, there's really not a lot of product early on in the reaction. And so again, this is all review and so down below. You can see that for our second assumption here. All it's saying is that we're going to be measuring the initial reaction velocity. And so this is really, uh, the main focus of biochemists when they're trying to study enzyme catalyzed reactions. And we know that the reverse reaction here, essentially from product backwards into enzyme substrate complex uh, that is controlled by K minus two is essentially ignored early on in the reaction, and instead, all we have is K one k minus one and k two to consider when we're considering, um, the initial velocity and so moving onto our third and final star or our third assumption, it is the steady state assumption which we covered in our previous lesson videos as well. So we know that this is just saying that the concentration of the enzyme substrate complex will remain constant. It will remain constant and because it remain, remains constant. That means that the rate of the formation or the rate constant for the formation of the enzyme substrate complex, will equal the rate of the dissociation of the enzyme substrate complex or the some of these two dissociation rate constants. And so again, we've already covered the steady state assumption in our previous lesson video. So this is all review. And so, looking down below, uh, noticed that we have the same graph that we had from our previous lesson videos for this third star and so we can see that we have in the blue here we have the pre steady state, uh, period, and then in the yellow. What we have is the steady state period and in the steady state period for the steady state assumption. We just say that the concentration of enzyme substrate complex and red here stays constant. And so, really, these are the three assumptions that we need to know. For the meticulous meant in equation moving forward in our course. And because we already are familiar with these from our previous lesson videos, it should feel a little bit like review, and so we'll be able to apply some of these concepts moving forward in our practice problems, so I'll see you guys there.

3

Problem

Which of the following options is not an assumption made in deriving the Michaelis-Menten equation?

A

The value of k

_{-2}can be ignored.B

The rate of ES formation = to rate of P formation.

C

The [E] is smaller than the [S].

D

a, b & c are all correct assumptions.

4

Problem

Michaelis & Menten assumed that the initial reaction for an enzyme catalyzed reaction could be written as shown:

Using this, the rate/velocity of ES-complex breakdown can be expressed by:

A

k

_{1}([E]_{T}– [ES]).B

k

_{1}([E]_{T}– [ES])[S].C

k

_{2}[ES].D

k

_{-1}[ES] + k_{2}[ES].