Glycogen Metabolism 2

So what happens when we actually need to use some of our glycogen when we need to mobilize our sugar stores? Well, that's where glycogen Foss for lace comes in. This enzyme breaks down glycogen by removing sub units again from the non reducing it right. So glycogen synthesis works that the non reducing and glycogen phosphor Ellis also works at the non reducing end. This isn't the last parallel you're going to see between these two enzymes. What's cool about language and frost for lace is unlike most enzymes. We've seen up to this point that cuts stuff right that cut stuff with water, usually like hydra laces. This is a phosphor lace. It cut stuff with phosphate, so it breaks things via phosphor license. Just a cool, cool thing. But it's also important, right? This is an arbitrary. Actually, it breaks off glucose sub units as glucose one phosphate, so they have the phosphate bound to them when they are, uh, cut away from glycogen. Why is this important? Well, how is glucose kept in the cell? Normally, it's immediately converted to glucose six phosphate. So the fact that it's coming off with the phosphate group attached is super important. Um, you might recall from previous page that the enzyme phosphate glue commute taste converts glucose six phosphate into glucose one phosphate prepping it for glycogen synthesis. Well, guess what? It does the same thing in reverse here, taking glucose one phosphate and turning it into glucose six phosphate. So, you know, this is a nice armory. So it has a delta G around zero. Readily reversible can go both ways. Um Lucayan, epinephrine and am p all stimulate phosphor list kindness. Be thio. Add to phosphate groups to foster for late glycogen phosphor Ellis. And when glycogen phosphor lace has those two phosphate groups attached, it becomes activated, right? So I just want you to think about something for a second. Glycogen synthesis becomes active when it's d phosphor related. Super important, right? Glycogen synthesis becomes activated when it's d phosphor related, whereas glycogen Foss for lease becomes activated when it's phosphor related. Okay, so the same process to both of these enzymes has an opposite effect. Why do you think this might be important? Well, let's think back to Glen Collis ISS and Glavany Genesis, right? We don't want glycogen, phosphor lace and glycogen synthesis running simultaneously, right? So if you phosphors late both or defrost for late both, you'll be able to regulate them perfectly because one will turn on, the other will turn off given each condition. All right, So glucose, actually al hysterically regulates, um, the enzyme glycogen, phosphor lace And it. What it does is it basically exposes the phosphate groups. It exposes the phosphate groups, uh, bound to the enzyme that activate it, and it exposes them to make them easier to remove. So it basically makes it easier to shut off glycogen phosphor lace. Now, if you think about this glycogen phosphor less breaks down glucose. Right. So if you have excess glucose, then that glucose is gonna lead to the shutdown of the glycogen phosphor lace again, just negative feedback. Right again and again and again and again, inescapable. It's everywhere. Biology. So uhh! One last note that I want to mention is if you think about it, glycogen has extensive branching, right? That means that there are many non reducing ends, right? Many available points for glycogen, phosphor, Alice or I should say, glycogen phosphor laces, many of them to attach thio and start cutting off glucose is That means that very rapidly with, like one, you know, with the hit of a signal, you can very rapidly produce a ton of glucose and mobilize it for the body. So essentially many of these enzymes will work simultaneously together to very quickly deliver a ton of glucose to the body. And you can see a model of glycogen phosphor lis working right here. And bear in mind that this is all glucose. I jump out of here for a second. Glucose one phosphate. Okay, so what about the branch points, right? Always. What about the branch points? Well, just like there's branching enzyme. There's D branching enzyme, and I know biochemists are the most creative with their naming schemes. But hey, at least you hear the enzyme name. You already know what it does, right? So deep It's genetic, By the way, it's geneticists who come up with funny names. Just just f y I that's really encounter the hilarious names and science scientists can have a sense of humor, too. So anyways, D branching enzyme will transfer three sugary, uh, three sugar units from one branch to another. So looking at our figure here, it'll take three sugar units, These three, and it's gonna transfer them up here right to a straight chain. And then it's going Thio, pluck off that branch point. And the interesting thing about this one particular glucose right there is when you break when it breaks that Alfa 16 bond, it produces the Onley true glucose in like a gentle isis. Right? So everything else comes off his glucose one phosphate, except this one Glucose comes off as just regular old glucose, and you can see the next thing that would the next thing that would have to happen is for this glucose to be phosphor elated, right? So that's that's not shown in the image. But that that would have to be the next thing occurring here. And, you know, this is just saying that glycogen foster for lace start cutting these off. Uh uh. Same is normal. So anyways, let's let's think big picture for a second. What does high blue blood glucose lead to? High blood glucose causes insulin to go up, which stimulates glycogen breakdown. And I'm sorry I said that wrong high blood glucose causes insulin to go up, so glycogen breakdown is lowered from this and glycogen synthesis goes up right. So insulin causes a reduction in glycogen breakdown and an increase in glycogen synthesis. So Oh, and also Glen Collis iss Low blood glucose causes glue Coogan to go up, which leads to glycogen breakdown and reduces Glen Collis ISS and glycogen synthesis. It's also going to stimulate glue konia Genesis, which is not written here. So I'm just gonna kind of add that in plus blue co neo Genesis glycogen Foss for lace and glycogen synthesis. We already said our phosphor related and D phosphor related together. But thes processes affect these enzymes in opposite ways, right? So it always leads to the activation of one and deactivation of the other. That way, these two processes air regulated, um, by a very simple mechanism that can control both of them and prevents futile cycles, which is always a very important part of metabolic pathways in the cell. All right, let's flip the page