Transcription
Our next polysaccharide is uh this one here called glycogen. So glycogen is another polysaccharide, and it's actually another polymer that uses glucose as its monomer. So glycogen is a polysaccharide, and just like starch, and just like starch again, the monomer is glucose, and polysaccharide using glucose monomers.
Now, what's the difference? Well, glycogen is what animals use to store their extra glucose. So while starch is the storage polymer for plants, glycogen is the storage polymer for glucose in animals. So this is what you and I, and your dog, and a cow, and you know, other animals do with extra glucose that they have that they don't need right now. They, instead of turning into starch, they turn it into glycogen.
Glycogen and starch are somewhat similar. They do, um, chain up with their glucose individual glucose rings holding their hands down, just like we saw in starch. But the difference is that the the chain is much more branchy. In starch, the glucose is just getting a long line and line up, and it's very linear, like a train or beads on a string. But in glycogen, you can see there's lots of branching going on. It's a much more kind of more like a network with lots of branches in all different directions. So it these are sort of hard to tell apart on a diagram. The way to look for look for them is that the, um, starch is just going to be single line like a train, whereas glycogen is going to have these glucose rings, but it's going to be much more branched.
Uh, where do we store glycogen? Um, so humans, mammals store glycogen mainly in their liver and in their muscles. That's where you store the majority of your glycogen. So what happens is if you eat a bunch of sugar, let's say you eat three Krispy Kreme donuts, five Krispy Kreme donuts, however many Krispy Kreme donuts, um, all that sugar and the glaze and everything goes into your, all those individual glucose molecules that make it taste so sweet, go into your bloodstream, and your blood sugar goes up. You have too much sugar in your blood. Um, you want some sugar in your blood, but too much is is a danger. And so your brain can sense that when the blood sugar goes too high, and it sends a message to actually your pancreas to create the hormone insulin. And the hormone insulin then goes to your liver and kind of knocks on the liver door, liver cells' doors, and says, "Hey, liver, you need to get glucose out of the blood." So the liver kind of opens its door, liver cells open their doors, in a way, and the glu, the glucose can be taken out of the bloodstream and put inside the liver cells where it's kept out of the bloodstream, so it's safer. And in the liver cells, the individual glucose rings are then hooked together to make this big, chainy, branchy glycogen molecule. And some of the, like, some of the glucose also is pulled out of the bloodstream and put in the muscles as well. Um, so that happens until your blood sugar comes down to a safe level.
Um, and then maybe it's been three or four hours since you've eaten those five Krispy Kreme donuts. And so as your blood sugar gradually drops down, your body will then go to the liver and say, "Okay, release some of that sugar back into the bloodstream." And those glycogen chains will get kind of nibbled away, glucose ring by glucose ring. There'll be hydrolysis, hydrolysis, hydrolysis, and those glucose will be released out one by one back into the bloodstream to maintain your blood sugar level at a kind of decent rate, so it doesn't go too low. That's hypoglycemia. It can cause a coma. And obviously, you you haven't got high blood sugar because you've already pulled the sugar out of the blood and stored it in the in the liver.
So the one difference here is that in terms of glycogen storage, you've only got one liver, and it's only a certain size. So if if I was a plant and I was storing my extra sugar, um, I can just make extra potatoes and hang them off my butt underground and keep adding potatoes and keep adding potatoes, um, to store all that extra sugar. But we can't add an extra liver and just hang it on the outside. So what tends to happen is if you eat, uh, a ton of sugar, uh, your body will try and get it out of the bloodstream and store it away as glycogen. But it will do that as much as it can until the liver is full. When the liver cells and the muscle cells are all full of as much glycogen as they can handle, uh, your body has two options. Uh, it can then take, if there's still too much sugar in the blood, uh, it can take some of that sugar and turn it into fat. So that's kind of like overeating too much sugar. Your body just stores what it can, and what it can't, it just turns to fat and stores on your butt and thighs, and that can just grow infinitely as a layer of fat. And in some cases, if your blood sugar is very uncontrolled, you can actually pee it out in your urine. And that's, um, not a good thing necessarily. Sugar in the urine is a sign that something's wrong with your sugar metabolism. It's kind of like a symptom of of diabetes.
So this is glycogen, the storage polymer of glucose for animals.