Polysaccharide

Concept: Concept

12m
Video Transcript

Hey guys in this video I just want to touch on polysaccharides and highlight a few of the most important polysaccharides that you might need to know. Alright guys, so you guys know what monosaccharides are by now and you should know a little bit about disaccharides but what about what we call polysaccharides, if it's more than two? Well, there are actually a few different categories that we need to be familiar with, they're very straightforward, this is going to be like this page in your packet, but let's just go through it trisaccharides. So, guys trisaccharides would be three monosaccharides linked through O glycosidic linkages, amazing, Oligosaccharides, that would be oligo, it's some. So, it's anywhere from between four and 10, like a few but not only three, it's a little more than three and then polysaccharides anything that is more than 10 monosaccharides in length would solidly be in polysaccharide territory. So, when you hear something is a polysaccharide that is a very long chain, usually, it's a very long chain of sugars that are all linked together through those O-glycosidic linkages, okay?

Now guys, that's pretty much where the definitions end and now what I want to do for the rest of this video is just highlight a few of the most important polysaccharides that you might come across in your biology major or your chemistry major or maybe even in your homework but this is more just for, just like the more you know, okay? So, polysaccharides that are created by plants specifically for use as an energy store, that's very important, it needs to used for energy, are known as starches you've heard of the word starch before. So, a starch is just the name for a polysaccharide that's made by a plant, not by an animal, by a plant for energy, it's a very specific category, okay? And so I'm going to show you guys some examples of that in a second and polysaccharides can have straight linkages and branched linkages, that's interesting, 1-4 linkages, we've seen these before disaccharides. Remember, that 1-4 linkages tend to make these nice straight chains. So, they tend to be straight polysaccharide chains whereas 1-6 linkages, I'll show you what a 1-6 linkage looks like in a second but it's way more bent up, it's going to make branched chains. So, as I'm showing you some examples of common polysaccharides it's going to be in the context of straight chains and branch chains, and just, you know, as I've already alluded to, the straighter the chain the harder it is usually the digest and the reason is because it's going to be stronger, it's going to be more dense, it's getting more difficult for enzymes to get in there, the more branched it is usually the easier it is to digest because it's easier for enzymes and fluids to get in between and hydrolyze okay, cool? So, that being said let's look at some common polysaccharides, and by the way guys, I'm going to show you three polysaccharides and notice that all I'm looking at here is polysaccharides of d-glucose, d-glucose, d-glucose. So, it's just funny that, it's crazy how many different types of polysaccharides there could be because all I'm showing you right now is d glucose but if I were to look at galactose or, or whatever other one that you want to look at you could have different has two polysaccharides for all the other sugars as well, so just keep in mind, this is just a very limited amount of them but these are some of the most common. So, what happens when a plant makes a long polysaccharide made of d-glucose and beta 1-4 linkages, okay? We've talked about these before, why we call it beta 1-4, because it is going in the same direction as the stereo descriptor, I'm linking the 1 and the 4. So, these are beta 1-4 linkages, we know that this is probably going to be strong, probably going to be strong linkages, right? Because they're very straight, does that make sense? Well guys, this is what we call, if you have a beta 1-4 linkage, this is what we call cellulose, have you heard of cellulose before? guys, cellulose is like the fiber of plants, okay? It is like it's what the cotton is made out of, it's what stems are made of, it's what leaves are made of, it's what wood is made of it's what paper is made out of, it's all made out of cellulose, does that sound very appetizing? not really. So, guys why do you think that this would be a good structure for wood and plants and fibers and all kind of stuff? because they're very strong linkages. So, does this count as a starch, do you think that cellulose counts as a starch? let's go through the definition, we said is it a polysaccharide? yes, is it made by plants? yes, is it designed as an energy store to be digested? No, because those linkages are so strong that they're going to be very fibrous and very impossible to digest, so this is not, I'm just going to put here, not a starch, okay? Instead, because it's not an energy store, cellulose is used for structural support, okay? It's used for structural support, it's used for cell walls, it's used to give rigidity to the structure, it's not eaten by anything? Well, it could be eaten, if you're like a termite or cockroach you could could eat cellulose but that's off topic, there are some specialized animals and creatures that can eat cardboard but most animals can't. So, that's why this is considered not of starch, cool? Awesome. So, let's go on to the next one. So, what we see is that here we have, once again, d-glucose linked together by, what types of linkages? you guys should be able to recognize this by now, these are alpha 1-4 linkages, right? So, what happens, if you have alpha 1-4 linkages and it's a d-glucose polysaccharide? Well, this is going to be called amylose, okay? And remember guys that these are essentially longer versions of your disaccharide. So, remember that d-glucose alpha 1-4 linkage would actually maltose, right? If it was a disaccharide but if you keep adding it's not called maltose anymore, it's called amylose, okay? So, question, will amylose count as a starch, what do you guys think? let's go through the definition, is it a polysaccharide? absolutely, is it made by a plant? yes, could this be used as an energy store? totally, because notice that it's matter of alpha linkages, what did we say about alpha linkages? you can digest those, the beta ones are kind of impossible but the Alpha ones are easy to digest, notice there's more kinks in it, it's not quite as straight. So, it's going to be easier so that just amylose is one of the major forms of starch. So, I'm going to put here, major form of starch, there are other forms of starch as well but this is one form of starch, cool? Is that making sense? Awesome. So, let's go down to another polysaccharide that might be important at some point. So, what happens if you take d-glucose, right? And you react and you from, sorry, not react it, you form a bunch of alpha 1-4 linkages just like amylose, so this is very similar to amylose, alpha 1-4 linkages, right? But every 10 or so sugars you throw in an alpha 1-6 linkage and what am I looking at, that's this guy over here. So, notice that this is considered an alpha 1-6 linkage because this is the, this is the carbon, this is the Alpha, why? Because it's going, let me just use a different color, it's going to trans to the stereo descriptor so it's alpha, except the one position of this carbon but notice what carbon is attached to on the other sugar, one, two, three, four, five, six, so this is a, this is an alpha 1-4 along with some alpha 1-6 that includes branching, okay? And guys it turns out that this is another really important polysaccharide that you might need to know called glycogen, and guys glycogen is the main energy store of human physiology, okay? So, whenever you eat a little bit too much and you have too much blood sugar going around, and you have like, you ate one too many Dunkin Donuts, your body is going to take that sugar, it's going to take that glucose and lock it up in the form of glycogen, glycogen can then later be used when you're starving or when you're hungry, when you need energy it can then be used to provide energy later, to be broken down. So, is glycogen a starch, what do you guys think, is it a form of starch? duh, it's definitely not a starch because made by animals. So, it's kind of like our, it's like the animal version of amylose, of starch, we have almost the same thing but we just add a few of those 1-6 linkages and now we call it glycogen, okay? So, I'm just going to put here, not starch, duh, okay? Because it's made by animals and starch can only be made by plants. So, this would just be, this isn't. So, this folds the other criteria it's a polysaccharide, it is an energy store but it's not called a starch because that would, it's made by animals, cool? And guys a lastly amylopectin is like the plant version of glycogen except instead of having branches every 10 monosaccharides it has branches more like every 30 monosaccharides, okay? Isn't it crazy how plants and animals are so different from each other, right? But, we have these structures that are so similar in function for plants they have amylose, which is a starch, amylopectin do you think amylopectin is also a starch? Totally, because it is made by plants, it's a polysaccharide and it's used as an energy store, right? It's like glycogen, it's used as an energy source, it's got alpha linkages that you can digest and then humans and all animal physiology, we have very similar structures except that we decided to put our 16 linkages every 10 sugars, which is minor difference but it means that we use glycogen and plants use amylopectin and amylose, cool? Awesome guys. So, I hope that this video helped polysaccharides come alive a little bit for you guys a little bit more and let's go ahead and move on.