Glycogen Synthesis Glycogenesis Pathway

Glycogen Synthesis Glycogenesis Pathway

Glycogen Synthesis Glycogenesis Pathway. Hey, everyone. In this lesson, we’re going to talk about glycogen synthesis, also known as glycogenesis. So the first thing we’re going to get into is what glycogen is, how it is actually synthesized. What are the enzymes involved in glycogen synthesis? Then we’re going to talk about where glycogen is stored in the body.

And then finallyzwe’re going to talk about what the role of glycogen is in our bodies. So to begin, here is a picture demonstration of what glycogen is actually looks like. And as you can see, it’s a very complex branching structure with a core enzyme. And we’ll get into what that core enzyme is in a moment. Now, glycogen, if you break down the word glycogen, it’s actually the prefix glyco means glucose, and then the suffix Gen means producing.

So it’s glucose producing. Now, in fact, glycogen is simply just a large polymer of glucose monomers. And glucose monomers can be arranged in a linear fashion with linkages of Alpha one four linkages. And it is also a branching structure, as I mentioned before, and the branch points are actually Alpha one six linkages. Now, the carbons are all numbered in a glucose molecule.

Glycogen Synthesis Glycogenesis Pathway

And again, as I mentioned before, the linear linkages are and the branching is Alpha one six. Another important thing to note is that glycogen has branching points at every eight to twelve glucose monomers, which is important because it distinguishes glycogen from similar compounds such as amylopectin. Now, glycogen, because of the word glucose producing, it, is in fact, a rapid source of glucose. And that’s the key about glycogen is actually a rapid source of glucose. And it is highly important because it actually maintains blood glucose levels.

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And during prolonged fasting, glycogen stores in our body typically only last about 24 hours, or a little less than 24 hours. Now, I mentioned before there’s an enzyme in the core of the glycogen. Now, this enzyme is called glycogenin, and I like to call this enzyme the catalytic core. And it’s, because it actually is an initiating enzyme in itself, begins the process of glycogen synthesis. And it does this by actually autoglycosylating itself.

And it’ll actually produce or attach chains of about ten to 20 glucose monomers to itself. And that’s how this whole glycogen synthesis process actually begins.

Glycogen Synthesis Glycogenesis Pathway So stepping back, we start with the glucose. Now, when a glucose enters a cell, it can actually be foster related by hexagonates or glucochinase, as we’ve learned before in other lessons, to glucose phosphate. Now I always like to call glucose phosphate the hub of many different signaling pathways. It, in fact, can be used for several different purposes. Now, the first thing it can do is actually it can go back and be defosphor related to glucose by glucose phosphate.

Synthesis of glycogen from glucose is called

A if glucose is needed, however, it can also go into other pathways. One of them is that glucose six phase can be processed into Glucone one five lactone and then shunted into the pentosphosate pathway. And if you haven’t watched that lesson, please do so, because it’s very important. Now, another pathway pretty much everybody is aware of is glucoseyx phosphate can be processed to fructoseix phosphate and then used for glycolysis for energy production. And the whole topic of this video, though, is that if it’s not used for any of these pathways, it can be used for glycogen synthesis by being shunted or processed into glucose one phosphate for glycogen synthesis.

Glycogen Synthesis Glycogenesis Pathway So if the glucose IV phosphate is used for glycogen synthesis, how does that actually happen? Well, the first thing that happens is that glucose II phosphate is acted on by the enzyme phosphoglucal mutates to form glucose one phosphate. And pretty much this enzyme simply just shifts the phosphate group from carbon six onto carbon one to form glucose one phosphate. Now it’s important to realize that this step is a reversible step, which means that glucose one phosphate can be reprocessed into glucose six phosphate if the cell requires free glucose. And this is important during glycogeny analysis,

Nevertheless, if glucose one phosphate is going to be used for glycogen synthesis, what’s the next step? Well, the next step is actually glucose one phosphate being acted on by UDP glucose pyrophosphorylase. Now, this is a very important enzyme. It takes UTP and it activates glucose. This is what we call the activation step.

Glycogenesis and glycogenolysis

Utp will actually attach a urine moyty to the glucose to form UDP glucose, the active form. So once we have UDP glucose, what is the next step? Well, the next step is glycogen synthase. This is a very important enzyme. And what it does is it actually will remove the UDP portion off of UDP glucose and add the glucose to actually a non reducing end of glycogen chain.

So what it does is it’ll actually just pop the UDP portion off of the UDP glucose, and it will actually pop the glucose monomer onto a non reducing end of a glycogen chain of glucose monomers. And it does this again in an Alpha one four linkage. It forms an Alpha one four linkage to actually extend the glycogen chain. And again, the glucose is actually added onto a nonreducing end. So all the carbons Besides carbon one are considered non reducing.

Glycogen Synthesis Glycogenesis Pathway But again, it is linked at an Alpha one four linkage. So once we have a very long glycogen chain, where do the branching points come from? I mentioned glycogen synthase attaches glucose to glucose with Alpha one four linkage. But I mentioned before branching point for Alpha one six. So how does that happen?

Well, if we can imagine a glycogen chain, very long glycogen chain with a glycogen in core, how does the branching points or where do the branching points come from? Well, simply there is something called a branching enzyme. Now, the branching enzyme, what it does is it’ll actually remove six to eight glucose molecules off of the terminal end of the long chain. So what it’ll do is it’ll actually chop off the last six to eight glucose molecules off a long glycogen chain, and then it’ll actually attach that chain, it chopped off back onto another chain of glycogen with an Alpha one six linkage. And that’s how the branching enzyme actually produces branch points.

Importance of glycogenesis

So that’s where we get the very branching structure of glycogen. And this is also very important to point out that with the more branch points and the more free terminal ends that glycogen actually has, it actually speeds up the rapid release of glucose. Now, in our example, instead of having one chain with one free glucose at the end where one can be removed at a time, now we have two points where two glucoses can be removed at a time. So the branching of glycogen actually speeds up the process or allows the cell to access more glucose quicker and faster. So that’s why it is actually a rapid source of glucose.

Now, the final thing I want to talk about is the UTP and UTP. Now, I mentioned before that UTP is used to activate glucose and UDP is actually removed off of the UDP glucose once the glucose is actually added to a glycogen chain. So that UDP glucose has to be recycled back to ATP, and it’s done so by the enzyme nucleoside diphosate kinase. And this enzyme requires one ATP to reform UTP. So I just wanted to tell you guys that just for sake of completeness.

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