in this video, we're going to introduce the enzyme glycogen phosphor, Alice. So Glycogen Foss for lease is an enzyme that catalyze is glycogen breakdown. And so, if we take a look at our image down below notice on the left hand side. Over here we have this large molecule that is a glycogen molecule and recall from our previous lesson videos that glycogen is a polymer that consists off individual glucose monomers. And so you can see that this one diamond right here represents a glucose monomer. And if we take a bunch of glucose molecules and we link them together in a chain like this, we can create our glycogen molecule and notice that the glycogen molecule is not only a single chain, but it also has branches coming off of the main chain here. And so we'll be able to talk Maura about glycogen structure later in our course. But for now, we can see that this is the glycogen molecule and glycogen phosphor lays, which is the enzyme. That catalyze is the breakdown of glycogen eyes right here. And so you can see it uses an inorganic phosphate here to break down our glycogen. And so notice that we have a shortened glycogen chain here because the glucose here at the end has been removed as, ah, glucose one phosphate. Now, the reason that we're talking about this enzyme glycogen phosphor list now is because glycogen phosphor lease is actually a classic example of an enzyme whose activity is controlled by both co Vaillant and Allah Hysteric regulation, making it a perfect opportunity for us to apply. Ah, lot of the concepts that we learned about in our previous lesson videos. And so we'll be able to talk more about this Covalin and Al Hysteric regulation later in our course. But what's important to know about this enzyme glycogen phosphor lease is that it actually has two different sub units, each of which has a specific Syrian amino acid residue, specifically Syrian 14. That can be fuss for elated and, of course, phosphor relation, we know is a post translational modification, Uh, and it's a type of co Vaillant regulation because there's Covalin attachment of a phosphate group in foster relation, and we'll be able to talk more about this phosphor relation and co violent regulation later in our course. Now this glycogen phosphor lease ends I'm, as we already have seen down below in our image. It uses glycogen polymer as a substrate, and it catalyze is the removal of a single glucose monomer. And so you can see it uses glycogen as the substrate, and it catalyze is the removal of a single glucose monitor. Now this glycogen phosphor lace enzyme is primarily expressed and liver cells and in muscle tissue, where glycogen breakdown is very critical, and we'll be able to talk Maura about glycogen breakdown in the liver and in the muscle later in our course. Now, what's important to know is that this glucose that is released by Glycogen Foster Worley's through subsequent reactions, the release glucose can be used in cellular respiration to generate energy in the form of ATP. And, of course, we know from our previous biology courses that cellular respiration is a very long process, with many different reactions, and we'll be able to talk about cellular respiration later in our course. But for now, what we can see is that this glucose that's released ultimately it can be used in many, many, many different reactions to generate ATP, which is energy and so ultimately what we're saying is that glycogen, phosphor lace it's activity can lead to energy for the cell through releasing this glucose. And so now that we understand the fundamentals of this enzyme glycogen phosphor lease on our next lesson, video will be ableto introduce the two different ISOS times of glycogen phosphor early. So I'll see you guys in that video.
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So now that we know that glycogen phosphor lays breaks down glycogen in this video, we're going to introduce the two different ISOS times of glycogen phosphor lease, which are liver glycogen, phosphor lease or liver. Phosphor roles for short and muscle glycogen, phosphor relates or muscle phosphor relates for short. Now, these two different ISOS times are going to be catalytic lee and structurally similar to each other. However, they are going to be genetically and Alice Terek Lee different from one another. And so, uh, this Alice Derek difference means that they're going to be regulated differently by different Alice Derek defectors. And so we'll be able to talk about the palest Eric regulation of these two isis times a little bit later in our course. But for now, if we take a look at our image down below, we can see the two different ISOS times on the left. Over here. What we have is the liver glycogen, phosphor relates Isis, I'm and on the right over here we can see we have the muscle. Glycogen, phosphor lays isis. I'm And so again, these air going to be catalytic lee similar or even catalytic Lee identical Isis times because they both catalyzed the same exact reaction that we talked about in our last lesson video of breaking down glycogen. And you can also see that they're structurally similar to each other because notice that they both have to sub units Azzawi can see here. And then they both also have these, uh, to searing amino acid residues that can be phosphor elated on. So you can see that the liver has phosphor elated Syrian residues and the muscle has, uh, Syrian residues that air, not phosphor related. But we'll be able to talk more about this phosphor relation later and our course. But for now, what I want you guys to notice is that the liver and muscle phosphor lays isis times. They're going to be regulated differently through different Alice Terek regulation, uh, due to their different biological rolls of glycogen breakdown. Now, later, in our course, we'll talk about the exact biological rolls of glycogen breakdown in the liver and the role of glycogen breakdown in the muscle. But for now, what I want you guys to notice is that the liver glycogen phosphor lays isis. I'm over here on the left is usually going to be in an active form unless it's Alice Terek Lee signaled to stop of being active and the muscle glycogen phosphor lace isis. I'm on the other hand, over here on the right, is usually inactive, so it's usually off unless it's al hysterically signaled to turn on and make at P for a muscle contraction. And so, if we take a look down below, uh, notice the liver glycogen fast for lease and Isis, I'm, we're saying, is usually active or on, and it's usually active or turned on, except when we eat a high carbohydrate meal. And we'll talk more about this exception a little bit later in our course. But for now, I want you to think liver glycogen Foster world is normally active or on, whereas muscle glycogen foster release over here is usually inactive or turned off except during a muscle contraction. And again, we'll talk about this exception mawr as we move forward in our course. But for now, we have a better understanding of these two isis times of glycogen phosphor lease, and in our next lesson, video will be able to talk more about the activity of liver versus muscle glycogen phosphor lease. Isis, I'm so I'll see you guys in that video
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So now that we've introduced both Isil seems of glycogen, phosphor lays the liver glycogen, phosphor leads Isis I'm and the muscle glycogen phosphor leads Isis. I'm in this video. We're going to introduce the phosphor lays a and the phosphor Lisbie forms of both. Isil seems. And so What's important to know is that both the liver and the muscle glycogen Foster Worley's isis times have two different forms. The first is going to be the phosphor lays a form, and the second is going to be the phosphor lease be form. Now each of these forms fast. Worley's A and Fast Worley's be exists in equilibrium with their own, our state and their own t state. And so, if we take a look down below it are image. We can see exactly what we've described above. So on the left, what we have is the liver glycogen, phosphor lays isis. I'm And on the right, what we have is the muscle glycogen phosphors. Isis. I'm and noticed that for both liver and muscle, we have the phosphor lays a form here at the top, which exists in equilibrium with its own, our state and T state, and then on the bottom. What we have is the phosphor relates be form, which exists again in its own equilibrium, with its own, our state and its own T state and notice if we take a look at the muscle glycogen phosphor lease. The same exact thing applies where on the top, what we have is fast for a an equilibrium with its own, our state and its own T state. And then we have phosphor. Let's be on the bottom, which exists in its own equilibrium, with its own, our state and its own T state. And so what you'll notice is that the phosphor lays a and the fossils be forms are actually inter convertible, meaning that we can convert fast Worley's A into fast for lease B and vice versa. And so, really, this inter conversion occurs through the addition and removal of phosphate groups on the searing residues. The two Syrian residues and so phosphate group addition and removal is a form of co Vaillant regulation. And so Covalin regulation is what converts fast Worley's A into phosphor Lisbie and vice versa. And so, if we take a look down below, it are Image noticed that the Foster Worley's A form on top can be converted into foster worlds. Be form on bottom through Covalin regulation. And so you can see that Covalin Regulation these up and down equilibrium Arrows will convert Foster Worley's A into phosphors. Let's be and noticed that really the only difference between foster lesbian Foster Worley's A is the fact that the Syrians are not phosphor related in phosphor Lisbie, whereas the Syrians are phosphor related in phosphor lease A. And so the same applies over here with muscle glycogen. Foss Worley's uh Covalin regulation regulates the conversion of Fast Worley's A Into Foss Worlds Be and vice versa. Now what I want you guys to notice is that phosphor lays a is going to have again phosphor related Syrians just as we see up above at the top here, they're all foster related, and that makes phosphor lays a catalytic, leam or active, and so you can think a here is for active. And that's because the equilibrium between the T state and our state, uh, in the face Worley's a form actually favors the our state. And so if we take a look down below at our phosphor lays a at the top up here. Notice that the equilibrium between the our state and T state actually favors the our state. Which is why we have this bottom arrow so much larger, uh, than the reverse equilibrium arrow. And so with the phosphor leads a form it's normally going to be in this our state, and the same applies over here with muscle. Isis on the phosphor lays a form. The equilibrium here is going to favor the our state over here. And so when we take a look at the fuss for Lisbie form, on the other hand on the bottom notice that it is unfussy for related. So it's not phosphor, elated as we can see down below. All of these Syrians here are not phosphor elated and also noticed that this makes phosphor lease be in the catalytic lee less active form. And that's because the equilibrium between the T state and the our state in the face worlds be form favors the T state. And so, if we focus on the bottom of our image down here and the B form, notice that the equilibrium between the our state and the T state eyes favoring the t state. And so that means that in phosphor Lisbie form, it's this t state that we will exist more often and the same applies over here as well. With the muscle isis I when it's in the face for Let's be formed, the equilibrium favors the T state. And so what you'll notice here in this image is that one of the differences between the two sides is the Covalin regulation. And so you'll notice that the Covalin regulation and liver favors phosphor elation. And so you can see that the equilibrium here for Covalin regulation is favoring the upwards direction here. And so that means that normally in liver cells, the Covalin regulation is going to be lied to phosphor relation. And so the phosphor lays a form is going to predominate in the liver. And so this yellow background that we have here is really suggesting the form that it's normally in. And so the liver, as we can see if we follow these equilibrium arrows, no matter which way we follow them, uh, using the larger arrow, it will always lead us back to this, um, form up here, the phosphor lays a our state and so in the liver, Uh, it will exist in this form right here in this form is almost like the on switch for the enzyme. So when it's in the face for lays a our state, it's in the most active form of the enzyme. So it's pretty much like the switch is on for the enzyme, and then notice down below. Over here, the foster worlds, BT State, is like the switch is off and so normally and liver it's on. But it can be Allah hysterically regulated and cove intently regulated to turn off. And if we take a look at the muscle over here, notice that we have the yellow background behind the phosphor. Let's be T state, and that's because in the muscle it's normally off. And so we can also follow each of these equilibrium arrows and notice that they will always lead to this form. Down here, the phosphor Lisbie t state in the muscle. And so it's normally off, however, again, through a lost Eric and Covalin regulation, we can turn it on when necessary. Example during a muscle contraction, and we'll be able to talk mawr specifically about the Alice Terek Regulation of both the muscle and liver isis times as we move forward in our course. But for now that concludes our introduction to the faucet, Worley's A and B forms. And again we'll be able to talk Maura about these forms as we move forward in our course, so I'll see you guys in our next video.
Glycogen phosphorylase is an enzyme involved in glycogen metabolism that’s regulated by phosphorylation. Phosphorylation on serine residues results in more enzyme activity, while the dephosphorylated enzyme has little to no activity. What result would you expect on activity if the serine residues that served as phosphorylation sites on glycogen phosphorylase were mutated to aspartate residues?
No effect on activity, since aspartate residues can be phosphorylated similarly to serine residues.
The enzyme would be completely inactive if it has an Asp residue, since it will no longer recognize its substrate.
The enzyme likely has some activity, since Asp is negatively charged like a phosphoryl group, but activity would not be regulated by phosphorylation.
The enzyme would be mostly inactive, since the enzyme can no longer be phosphorylated.