Hey guys, it's Medicosis Perfectionatus where medicine makes perfect sense. Let's resume our biochemistry playlist. In previous videos, we talked about the properties of the enzyme, the nomenclature or the classes of enzymes. We talked about the mechanisms of enzyme activity. We talked about the two theories.
Number one, the key and the lock theory. Number two, the induced fit theory. Today we'll turn our attention to enzyme kinetics and those crazy graphs that everyone hates. And we'll start with Michaelis-Menten equation. With that said, now let's get started.
This is my biochemistry playlist. Please watch these videos in order. Most enzymes in your body are proteins.
Enzymes are catalysts indeed. They speed the rate of the reaction by lowering the activation energy. However, they do not... change the equilibrium, nor do they change the overall free energy.
The enzyme is like a shortcut. It's a catalyst. It increases the rate or the speed of the reaction.
For the purpose of your biochemistry exam, the rate is the same as the speed, is the same as velocity, and we will symbolize this as V. But, Heberikos, speed and velocity are different. I know in physics they are different, but in biochemistry... no one cares because biochemists suck at physics.
Here is the enzyme. It lowered my activation energy but did not change the overall energy or the delta G. You still went from A to B.
A is the initial state, B is the final state. Both of them could be called ground state, but when you go uphill, it's called the transition state. Enzymes are specific. One enzyme for one reaction or one type of reactions.
Enzymes do indeed love their substrate, and this love relationship is known as affinity. So, we can say that the enzyme urease has affinity for urea, its substrate. We talked about the six categories of enzymes before.
Never ever forget that kinases add phosphate to the reaction, therefore they are transferases, they are transferring a phosphate. Conversely, a phosphatase is an enzyme that breaks down, plus takes away a phosphate from you by hydrolysis. So it's a hydrolase.
This is the active site, which is the front door, but this is the back door or allosteric site. Who's gonna occupy the active site of the enzyme? The answer is the substrate. When the substrate binds the enzyme, they make an enzyme-substrate complex.
They literally hug each other. And we discussed the two models for enzyme-substrate interaction. The old one is the key in a lock, a truck in a dock, a hand in a glove, which is not very accurate. The more accurate one is the induced fit model.
When they hug each other, the substrate is gonna change the active site of the enzyme, and the active site will change the substrate shape. Here is the Michaelis-Minton graph. Oh my goodness, I have this!
Shut up and calm your butt down. It's easy. Some basic math.
When you have a relationship like this between A and B, and you have a line going this way, it's a direct relationship. Translation. Suppose that we started with this point.
Let's call it 1. You go up here, you will intersect with this point. Let's call it 1. However, let's increase B, for example. All right?
If I increase B, What do you think is going to happen to A? Well, well, well, let's intersect. Oh, I see here. The 2 is higher than 1. Therefore, as I increase B, A increases 2. Direct relationship. Conversely, if you find the relationship between them, and the line is going downwards like this to the abyss, it is inverse relationship.
Let's play with this equation. Between A and B, there is a direct relationship. as long as C is constant. Next, between A and C, there is inverse relationship, as long as B is constant.
How about the relationship between B and C, direct relationship, as long as A is constant? Can we do this with a plus sign in between? Yeah, same thing. Between A and B, inverse relationship, as A goes up, B goes down, and vice versa, provided that C is constant. Between A and C, there is direct relationship, between b and c there is direct relationship how do i remember all of this whenever you have two entities that are divisible by each other or subtractable from each other the relationship between them is direct conversely if they are multiplicable by each other or additive to each other it's an inverse relationship now let's look at this graph oh wait medical This is a line going to the sky, not to the abyss.
No, no, no. It's going to the sky. Therefore, between the substrate concentration and the initial velocity of the reaction, there is a direct relationship, especially in the beginning, because this first portion looks as if it's a straight line. In real life, you do not have just one substrate. You have gazillions of these.
And it's not just one enzyme. You have gazillions of these. Therefore, we can argue that The more substrates we have, the faster the reaction, i.e. direct relationship. The greater the concentration of the substrate, the faster the rate of the reaction, direct relationship. But hey, Miracosis, why didn't we keep going up, up, up?
Why did we plateau? Why did we level off and flatten out like this? Great question.
Because enzymes are proteins. Eventually, they can get saturated. Do you remember my biology playlist? Remember when we talked about cell membrane transport? We had passive transport, no energy needed, and we had active transport, we needed energy.
Do you recall the passive transport? Yeah, we had simple diffusion, we had osmosis just for water, and we had facilitated diffusion. What was the difference between simple and facilitated?
Yeah, Maricosas, it was true that both of them required no energy. Both of them happened along their electrochemical gradient. However, simple diffusion required no carrier protein.
However, facilitated diffusion did require a protein carrier. And this carrier protein will give you what? Specificity, like the enzyme, because enzymes are proteins, just like a carrier. A carrier is a protein, an enzyme is a protein.
Both of them will give you specificity. What else? Competition. What else? Saturation.
you level off. This is why you hit your maximum, the max. Simple diffusion is a straight line going to the sky, it never stops.
However, facilitated diffusion, because it's dependent on carrier proteins that eventually will get saturated, these carrier proteins will get sick and tired of being sick and tired, and they will level off. If you have watched my kidney physiology lectures at medicalsaysperfectionaries.com, We talked about the proximal convoluted tubule. Look at this. Glucose is being transported, and it needs a carrier known as SGLT. S for sodium, GL for glucose, T for transporter.
This transporter is a protein. Eventually, if you have too much glucose, you will saturate all of your transporters because they are proteins. They get sick and tired of being sick and tired.
And that's why the transport... the reabsorption of glucose will go up until you saturate all of your proteins, and then you level off, and then you plateau, and then you hit your V maximum. What should I do next?
I cannot reabsorb glucose any longer. You will start to lose this glucose in your urine. Oops.
So, you cannot just expect to raise your serum glucose ad infinitum and expect the kidney to reabsorb all of it. It's not going to happen. The kidney will try her best until the kidney saturates all of her SGLT2, and then you will level off, and the extra glucose will end up in the urine. The legend has it that the ancient Egyptians were the first people to develop the pregnancy test. The idea was very simple.
If you want to know if this lady is pregnant or not, take a sample of her urine. It's a physiological fact that during pregnancy, the kidney will lower the threshold for glucose, i.e. glucose will start to appear in the urine earlier than expected. These SGLT2 carriers will get saturated earlier than we expected.
So if the lady is pregnant, there will be glucose in the urine. We will add her urine to some plants, could be wheat. could be barley if the barley grew it means there was sugar in the urine the barley ate the sugar and the barley grew but if the barley did not change it means there was no glucose in the urine and she's not pregnant it's all about the vmax baby now back to michaelis freaking menton this is why you level off this is why you plateau because you saturated all of your enzymes which are proteins and this is called vmax.
but let's go back to step one. between the substrate concentration and the Velocity is a direct relationship. Here is another math fact.
If I say that A is directly proportional to B, I can remove this proportional sign and put equal and multiply by constant. So now this will become A equals constant multiplied by B. Can we do the same thing for Michaelis-Menten? Sure. Since the velocity or the rate of the reaction is directly proportional to the substrate concentration, I can remove this proportional sign.
and put equal constant multiplied by. So it becomes V0, or V0, which is the initial velocity, equals constant times the saturation. In the German language, and I believe in Latin, constant could be written with a K.
That's why we still have EKG or ECG. It's the same concept. Encephalogram or encephalogram, same origin. K or C, they are cousins. So the constant is K.
Why do you call it Km? Why not Fu? Because this is the constant of Michaelis freaking Menten.
Oh, they named it after them. That's right, the constant of Michaelis-Menten. The Michaelis-Menten constant, multiplied by the substrate concentration. Still, the relationship between the substrate concentration and the rate of the reaction is direct.
If the substrate concentration goes up, the reaction rate goes up. and vice versa. Michaelis-Menten started with this, and then with experimentation and mathematical proof that took about 10 steps, which is beyond the scope of this video, they arrived at the Michaelis-Menten equation, which is this.
If you want me to make a separate video to describe the 10 steps of the mathematical proof, I can do it. But for now, please memorize this Michaelis-Menten equation. This is the initial rate or initial velocity.
This is the maximum rate of the reaction. substrate concentration, Michaelis-Menten constant. Let me tell you the truth, you will never reach V-maximum in practical terms.
Theoretically, yes, you can hit it, but practically speaking, when we're talking about just biochemical enzymes, you're not gonna hit it, because you have gazillion enzymes in your body. So instead of talking about V-max, which is a theoretical point, why don't we go back to Earth and talk about half of V-max, because we can actually reach this in the lab. All right.
All right, let me take half of Vmax, which is this number, times half. Now I'm here. Let's go hit the graph and then intersect with the x-axis.
What should I call this point? This is the McAllisman constant. Therefore, instead of V, I'll write half Vmax because I'm getting practical now.
And this is the same as this. By dividing each side by Vmax, we will get the Vmax from here. Cancel it with this Vmax. Then half equals...
substrate concentration over Km plus substrate concentration. Do some scissors action. 1 times Km plus S equals 2 times S. Therefore, Km plus S equals S plus S, which means Km is almost the same as S.
That's exactly right. If you do not believe me, just look at the graph. S is on the x-axis.
Km. is also on the x-axis or horizontal axis. Therefore, Km is the same as substrate concentration, provided that we're talking about a velocity that is half of Vmax. Oh, Medicosus, this makes so much sense. Even if you slept throughout the lecture so far up to this point, you can still answer every question correctly on your exam.
Just listen to me carefully. Enzymes are catalysts. I know that. They boost the speed of the reaction. I know that.
The more enzymes you have, the faster the reaction, i.e., the greater the V. Makes sense. The greater the number, the greater the Vmax. The lower the number of enzymes, the lower the Vmax.
Listen to me carefully. Enzymes are specific for the substrate. They really love substrate. Urea's enzyme will not work with any substrate except urea. What do you call this love relationship?
Affinity. We can assess affinity by Km. however they are inversely related the higher the affinity the lower the km the lower the affinity the higher the km let's put all the equations here please pause and review and now let's look at the graph here's the control line okay if i draw graph a for you what do you think happened to vmax in order to understand what happens i'll take the same point from the x-axis and i will go up and then you hit b and you go to the y-axis, and then you hit the control, go to the y-axis, and then you hit A, and go to the y-axis.
Which one has the greatest Vmax? A or B? Or the control? Of course A.
Therefore, As you shift the curve upwards, you're increasing the Vmax. Conversely, when you shift the graph downwards, you are lowering the Vmax. Let's play the same thing with the Km.
Let's do this. Now, to understand what's happening to the Km, I'll take the same point on the y-axis, and then you go here until you intersect with this x graph, which is the dark green. That's my x.
And then you go here, here, here, here, here, until you hit the control. That's my control. and then you go here, here, here, until you hit the y, and that's the y. Which one has the highest Km?
Again, Km is seen on the x-axis. Of course, y has the highest Km. And you remember that Km is inverse related to affinity, which means that graph y has a higher Michaelis-Minton constant, but a lower affinity.
Conversely, graph x has a lower Km, but a higher affinity. Put all of them in one slide. If you shift that graph upwards, you're increasing Vmax, which means what?
You're increasing the number of enzymes because they are directly related. Conversely, shift that graph downwards, you're lowering the Vmax, and you're decreasing the number of enzymes. Can you give me examples of shifting the graph upwards?
Yeah, induction, more gene expression, make more enzymes, DNA, make more, code for more. How about upregulation? Oh, more enzymes.
That's true. More Vmax. Conversely, examples of lowering the Vmax is repression of the genes that code for that enzyme, downregulation of the enzyme, or non-competitive inhibition, which will be the topic of an upcoming video.
Now, let's turn our attention to shift to the left versus shift to the right. When you shift to the left, you're lowering Km, which means you're increasing affinity. Hashtag activation, potentiation, or sensitization. They love each other even more.
But when you shift to the right, yes, indeed, KM is rising. However, affinity is dropping. Inactivation, competitive inhibition, desensitization. Slap the equations on the slide, and now you can kiss Michaelis Menten goodbye. You can throw Michaelis and Menten in the dustbin of history where they belong.
It's over, baby. This graph will help you answer every question correctly. If you want to download these colorful notes, they are available at medicosisperfectionalist.com.
In the next video, we'll talk about Linwee the book plot where everything is reversed. Everything is upside down. If you want to learn more about the SGLT2 and the GLUT2 receptors, check out my renal physiology course at medicosisperfectionalist.com. You can also download my general pharmacology course where we have more graphs, my antibiotics course, and my brand new surgery high yields course at medicosisperfectionaries.com. For a limited time, you can get a 40% discount towards any course by using promo code TOXIDROME at checkout.
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