You must have already heard about simple and complex carbohydrates. Starch is the most common type of complex carbohydrate which is present in the food you consume. So, these complex carbohydrates consist of severely branched molecular structure. They are nothing but the polysaccharide itself. They are complex carbohydrates formed with a chain of monosaccharides. The bonds that keep the chain together are glycosidic. Some common polysaccharide examples are starch, glycogen, and cellulose. Homopolysaccharide and heteropolysaccharide are the two fundamental types of polysaccharide. In this article, you can learn about polysaccharide in detail, their structure, types, and examples and so on.  

What is a Polysaccharide?

Polysaccharides are nothing but complex carbohydrates, formed with a chain of monosaccharides. Glycosidic linkage is what keeps the chain of monosaccharides bonded together. You can say that a molecule of a polysaccharide has a certain number of sugar molecules that come together to form a larger molecule. You can also call them Glycans. Polysaccharides get classified into two parts, which are, homopolysaccharide and heteropolysaccharide. Below you can learn more about the same. 

Types of Polysaccharides

  • Homopolysaccharide: In this type, molecules get formed with a single type of monosaccharides. You can determine a general theme for such molecules by studying their monosaccharide units. When homopolysaccharide gets formed using nothing except glucose molecules, then you can call it as Glucans. If it uses galactose molecules while forming, then you may call it Galactus. In the topics below, you can find plenty of explanations about Glucans.   

  • Heteropolysaccharide: These are polysaccharide molecules consisting of more than a single kind of monosaccharides. Hyaluronic acid, heparin, and chondroitin sulphate are some common examples of the heteropolysaccharides.   

Structure of Polysaccharide:

Following is how a typical polysaccharide structure looks –

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Every polysaccharide gets formed with the same process. In which the monosaccharides form a chain using glycosidic bonds. These bonds have oxygen molecules bridging the two carbon rings. The bond gets created when the carbon of one molecule loses the hydroxyl group, and the hydroxyl group of a different monosaccharide loses the hydrogen. Since two molecules of hydrogen and one molecule of oxygen get expelled, it becomes a dehydration reaction. The obtained structure of molecules tells you about the various properties and structure of the final polysaccharide.    

Polysaccharide Examples

Now that you have learned what a polysaccharide and its structure is, it’s the time to learn about polysaccharide examples. Naturally, there are three main polysaccharide. You come across them every day in your life, and they are starch, glycogen, and cellulose. Below you can read about them in detail. 

  1. Starch

You can find starch in all photosynthetic plants. Roots and seeds of the plant have more starch in general. When plants synthesize glucose, excessive glucose gets stored in the form of starch. It consists of a linked glucose molecule, and that’s why it’s a glucan. 

The molecular formula for starch is (C6H10O5)n. Here, the ‘n’ indicates the number of linked molecules. Below is a typical structure of starch. 

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You can find starch in the seeds of plants as granules. Upon heating those granules in water, you get a colloidal suspension. Further, you get two components from the process, Amylose and Amylopectin. 

  1. Glycogen

Glycogen is a glucan, which exclusively contains D-glucose units. It acts as a reserved source of carbohydrates for plants as well as animals. Below you can see the structure and function of glycogen. 

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The structure of glycogen is quite similar to amylopectin. However, the branching takes place more frequently in a glycogen molecule. As you can see, it is indeed a larger molecule. Glucose molecules are small in size, and they can diffuse out of a cell membrane. Since glycogen is bigger, it doesn’t diffuse out of the cell membrane. It serves an essential function of storing glucose within cells. 

  1. Cellulose

Cellulose is a crucial structural component of the cell walls plants that are photosynthetic. It is fibrous in nature and highly insoluble in water too. Keep in mind that cellulose is a glucan. The D-glucose units have connections in the (1 – 4) fusion. It is a beta linkage, and it’s indeed different from the glycogen. 

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The structure of cellulose –OH group, points outwards from the chain structure. When two chains come in contact with each other, they get stacked on each other because of the hydrogen bonding between hydroxyl groups. In the end, you obtain an insoluble fibrous structure which is perfect for the functions of cellulose in the cell walls.  

FAQ (Frequently Asked Questions)

1. Define Polysaccharide and State Their Types.

Polysaccharide is nothing but complex carbohydrates. They comprise repeating units of monosaccharides which get attached by Glycosidic linkage. A single molecule of a polysaccharide has x number of sugar molecules bound together to create a bigger molecule, known as Glycans. Polysaccharides can get divided into two parts, homopolysaccharide and heteropolysaccharide. The homopolysaccharides found in plants are starch and cellulose, whereas glycogen and chitin are present in animals. Some commonly found heteropolysaccharides are hyaluronic acid, heparin, chondroitin sulphate, and keratin sulphate. 

2. What’s the Difference Between Homopolysaccharide and Heteropolysaccharide?

Typically, polysaccharides can get classified into two types, which are homopolysaccharide and heteropolysaccharide. The latter consists of more than one kind of monosaccharides. And the homopolysaccharides consist of only a single type of monosaccharide. Depending on the monosaccharide they have, you can determine the general theme. For example, Glucans are the homopolysaccharides made out of nothing but glucose molecules. Nevertheless, the fundamental difference between homopolysaccharide and heteropolysaccharide is that the former uses one type of monosaccharide, and the latter one uses multiple of them.