Polysaccharide: Study with Video Lessons, Practice Problems & Examples

Polysaccharides, the largest carbohydrate class, consist of over 20 covalently linked monosaccharides, often exceeding 1,000,000 units. They can be categorized into homopolysaccharides, made of one type of sugar, and heteropolysaccharides, composed of multiple sugars. Differences among polysaccharides arise from the identity of sugar units, types of glycosidic bonds, chain length, and branching degree, influencing their physical and chemical properties. Functions include structural support and energy storage, highlighting their significance in biological systems.

Polysaccharide

In this video, we're going to begin our lesson on polysaccharides. So recall from our previous lesson videos that polysaccharides are the largest size class of carbohydrates containing more than 20 covalently linked monosaccharides. Polysaccharides can be quite enormous, sometimes containing more than 1,000,000 sugar units. But, really, other than being enormous, polysaccharide composition is actually relatively simple, especially in comparison to oligosaccharides, which might be a little bit surprising to you guys. As we'll see moving forward in our course, polysaccharides usually consist of just 1 or 2 different types of monosaccharides and these 1 or 2 different types of monosaccharides are going to be repetitively linked together to create these large polysaccharide structures. Because they contain just 1 or 2 different types of monosaccharides, that makes their composition relatively simple. But you might recall when we talked about glycoconjugates and oligosaccharide portions of glycoconjugates that they're very heterogeneous and they usually contain a variety of different types of monosaccharides, usually more than 2, and that is what makes the oligosaccharide composition more complex. Now as we move forward in our course and talk about specific polysaccharides, we'll find that their functions are going to include structural support or acting as energy storage molecules. Notice down below, we have an image over here of a linear form of a polysaccharide where you can see you can have the same exact sugar units just repetitively linked together creating the long chain. And then over here, you can see that we have another polysaccharide that is branched, creating all of these different branch chains, so not forming the linear chains. This seems to be made up of multiple different types of sugars. As we move forward in our course, we're going to continue to talk more and more about polysaccharides. So I'll see you guys in our next video.

Polysaccharide

In this video, we're going to talk about how polysaccharides differ from each other. And so polysaccharides can actually differ from each other in at least one of the following four ways that we have listed down below. And so the first way that they can differ from each other is in the identity of their reoccurring sugar units. And so whether these sugar units are d-glucose molecules or some other sugar molecule, that is going to be one way that the polysaccharides can differ. Now, the next way that the polysaccharides can differ is in the types of glycosidic bonds that are linking together their sugar units. And so whether these are alpha-1,4-glycosidic bonds or if they're beta-1,4-glycosidic bonds, that is going to be another way that these polysaccharides can differ. The third way that the polysaccharides can differ is in the length of their chain. So, basically, in the total number of sugar units that the entire polysaccharide molecule contains. And then the fourth way that polysaccharides can differ from each other is in the degree of branching that occurs in the polysaccharide structure. And so moving forward, we'll be able to see different polysaccharides that vary in each of these four different categories. And so it's important to note that each of these four different factors will actually influence a polysaccharide's physical and chemical properties. And so that's important to keep in mind, again, as we move forward and discuss specific polysaccharides. And so that concludes our introduction to how polysaccharides can differ from each other and again, we'll continue to learn more about polysaccharides as we move forward. So I'll see you guys in our next video.

Polysaccharide

In this video, we're going to distinguish between homopolysaccharides and heteropolysaccharides. And so, in general, there are two major categories that all polysaccharides could fall under. The first is going to be homopolysaccharides and the second is going to be heteropolysaccharides. Now, homopolysaccharides, recall that the prefix homo means the same and so these polysaccharides consist of repeating units of only one single type of monosaccharide sugar and so it's going to be the same exact sugar that is repetitively linked over and over again. And so as we move forward in our course, we'll find that homopolysaccharides usually function as intracellular structures and or as energy storage molecules. Now, heteropolysaccharides, on the other hand, recall that the prefix hetero means different and so heteropolysaccharides consist of greater than two different kinds of monosaccharides repetitively linked together. And so as we move forward in our course, we'll find that heteropolysaccharides usually function as extracellular structures, meaning that they form the structures on the outside of the cell, whereas homopolysaccharides, they are forming the structures typically on the inside of the cells.

So, we take a look at our image down below over here on the left-hand side. Notice that we're showing you homopolysaccharides because we have the same exact blue sugar unit repetitively linked, over and over again. Now, notice that we have an unbranched form here which is just a straight linear chain with no branches coming off. But then you can also have branched homopolysaccharides, which you can see there is a branch chain coming off of the main chain. Now over here on this side, what we have are, of course, heteropolysaccharides. And so you can see that the heteropolysaccharides are going to contain greater than or equal to two different kinds of monosaccharides. And so you can see that we've got, the yellow and the blue monosaccharide linked together. This is an unbranched chain. As you can see, there are no branches coming off and this is a linear. And then over here on the right, what we have is the branched heteropolysaccharide. So you can see it's made up of more than one sugar unit and, it is indeed branched since there is a chain coming off of the main chain. And so, again, as we move forward in our course, we're going to see examples of both homopolysaccharides and heteropolysaccharides as well. And so that concludes this video, and I'll see you guys in our next one.

Here’s what students ask on this topic:

What are polysaccharides and how are they classified?

Polysaccharides are the largest class of carbohydrates, consisting of more than 20 covalently linked monosaccharides, often exceeding 1,000,000 units. They are classified into two main categories: homopolysaccharides and heteropolysaccharides. Homopolysaccharides are composed of repeating units of a single type of monosaccharide, while heteropolysaccharides consist of two or more different types of monosaccharides. These classifications help in understanding their functions, which include providing structural support and serving as energy storage molecules in biological systems.

How do polysaccharides differ from each other?

Polysaccharides can differ in four main ways: the identity of their recurring sugar units, the types of glycosidic bonds linking the sugar units, the length of their chains, and the degree of branching in their structure. These differences influence their physical and chemical properties. For example, the type of glycosidic bond (α or β) can affect the digestibility and solubility of the polysaccharide. The chain length and branching degree can impact the molecule's compactness and its role in biological systems, such as energy storage or structural support.

What are the functions of polysaccharides in biological systems?

Polysaccharides serve several crucial functions in biological systems. They provide structural support, as seen in cellulose in plant cell walls and chitin in the exoskeletons of arthropods. They also act as energy storage molecules, such as starch in plants and glycogen in animals. Additionally, polysaccharides can play roles in cell signaling and recognition processes, contributing to the overall functionality and health of organisms.

What is the difference between homopolysaccharides and heteropolysaccharides?

Homopolysaccharides consist of repeating units of a single type of monosaccharide, making their structure relatively simple. They often function as intracellular structures or energy storage molecules. In contrast, heteropolysaccharides are composed of two or more different types of monosaccharides, resulting in a more complex structure. These polysaccharides typically function as extracellular structures, forming components outside the cell, such as in the extracellular matrix or cell walls.

What factors influence the physical and chemical properties of polysaccharides?

The physical and chemical properties of polysaccharides are influenced by several factors: the identity of the recurring sugar units, the types of glycosidic bonds (α or β) linking the sugar units, the length of the polysaccharide chain, and the degree of branching. These factors determine properties such as solubility, digestibility, and structural integrity. For instance, cellulose, with β-1,4-glycosidic bonds, is rigid and insoluble, providing structural support in plants, while glycogen, with α-1,4 and α-1,6-glycosidic bonds, is highly branched and soluble, making it an efficient energy storage molecule in animals.