Pearson+ LogoPearson+ Logo
Start typing, then use the up and down arrows to select an option from the list.


Learn the toughest concepts covered in Biochemistry with step-by-step video tutorials and practice problems by world-class tutors

Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism

Glycogen Metabolism 1


Play a video:
Was this helpful?
let's continue our story of metabolism with glycogen, the storage molecule that contains glucose. Now, glycogen is a highly branched structure. And the reason for this is actually because it saves a lot of space in the cell to have all this branching. Uh, now, the straight chains of glycogen are made with Alfa One for, like, acidic linkages between the glucose units, whereas, uh, the branch points on the molecule have Alfa 16 Glick acidic bonds. Now, the sugar chains tend to be about 12 to sub units long. So, looking at this figure here, you know, imagine that each one of these little chains is about 12 to 14 units long. So the core of glycogen is actually a protein and it's protein called glycogen in, and you can see it right here the center of our glycogen and the first sugars of glycogen are actually hooked onto tyrosine residues in glycogen. In now, glycogen is made by glycogen synthesis, and this is a synthesis, meaning it doesn't use nucleotide triphosphate instead, excuse me. Nucleotide triphosphate like ATP. Instead, it uses something called UDP glucose. So that's your still die phosphate glucose. And UDP is actually released from the reaction. Now it elongates the the strands of sugars at the non reducing end. And as we already said, it usually forms chains about 12 to 14 sub units long now, uh, G s K three normally Foss for lates and in activates glycogen synthesis. You might remember this from bio signaling insulin, right? The indicator of high blood sugar inhibits GS K three. And that's how glycogen synthesis is activated. So insulin inhibits the thing that inhibits glycogen synthesis. And then glycogen synthesis can take that sugar out of blood and store it as glycogen. Now protein, phosphate taste one defrost for lates glycogen synthesis. So it's gonna inactive are right. Uh, it's going to activate it. So G s K is the thing that in activates glycogen synthesis But protein, phosphate, that protein phosphate tastes one rather has to actually activate has to actually turn on glycogen synthesis and protein foster taste. One is stimulated by insulin. So, you know, let's think about this for a second. Insulin turns off the thing that shuts down glycogen synthesis, and it turns on the thing that turns on glycogen sent base Pretty cool, right? So and just You know, this speaks to what we were talking about previously with bio signaling about how maney how one signaling molecule can lead to the activation of so many different things. Right. Um, so anyways, uh, protein phosphate ace one is stimulated by insulin. Also, glucose six phosphate. So think about it. As soon as glucose enters the cell, it's gonna become glucose six phosphate. Uh, if there's a build up of glucose six phosphate, it's going to stimulate protein phosphate taste one to turn on glycogen synthesis to get it to start storing some of that glucose on. Obviously, it's also stimulated Bye bye, glucose, and it's inhibited by glue Coogan and epinephrine. So blue Coogan and epinephrine are both molecules that cause blood sugar to go up right there, released in response to low blood sugar to try to raise the blood sugar so clearly you don't want glycogen synthesis running. If you want your blood sugar higher, you wanna be mobilizing the sugar, not storing it. And you can see a little diagram of how glycogen synthesis fits into our model of, um, Glen Collis issue. Here we have Texas kindness and then to actually convert it into convert the glucose into glycogen. It has to go through a few steps. You don't again. You don't actually need Thio. Worry about the specific mechanism. Just know that glycogen synthesis uses UDP Glucose leaves udp behind and it adds a glucose sub unit onto the sugar chain. So that's all well and good. We've been talking this whole time about how to make straight change sugars. But as we said in the beginning, glycogen has branched. So how does glycogen make those branches? Well, simply with branching enzyme, which basically takes, uh, 6 to 10 sub units of sugar. Uh, you know, the chain formed blight by glycogen synthesis, and it transfers those sub units onto the sixth position of a glucose. So you can see here in black, we have our straight chain. And here is that portion that was transferred. I mean, of course, here we're only showing three. But as we said, it transfers about 6 to 10 sub units and it attach. Is it at that six position? So you form an Alfa 16 bond, so branching enzyme just transfers. It doesn't actually build the polymer like like a Jensen face does. All right, let's turn the page