What is a polysaccharide? The use of polysaccharides and their significance

There are four main classes of complex bioorganic substances: proteins, fats, nucleic acids and carbohydrates. Polysaccharides belong to the last group. Despite the “sweet” name, most of them perform completely non-culinary functions.

What is a polysaccharide?

Substances of the group are also called glycans. A polysaccharide is a complex polymer molecule. It is composed of individual monomers - monosaccharide residues, which are combined using a glycosidic bond. Simply put, a polysaccharide is a molecule built from the combined residues of simpler carbohydrates. The number of monomers in the polysaccharide can vary from several tens to one hundred or more. The structure of polysaccharides can be either linear or branched.

Physical properties

Most polysaccharides are insoluble or poorly soluble in water. Most often they are colorless or yellowish. Most polysaccharides do not have a smell and taste, but sometimes it can be sweetish.

Basic chemical properties

Among the special chemical properties of polysaccharides, hydrolysis and the formation of derivatives can be distinguished.

• Hydrolysis is a process that occurs when a carbohydrate interacts with water with the participation of enzymes or catalysts such as acids. During this reaction, the polysaccharide breaks down into monosaccharides. Thus, we can say that hydrolysis is the reverse of polymerization.

Glycolysis of starch can be expressed by the following equation:

• ( _{6 10 5} ) _n + n ₂ = n _{6 12 6}

So, in the reaction of starch with water under the action of catalysts, we obtain glucose. The number of its molecules will be equal to the number of monomers forming the starch molecule.

• Derivation may occur during the reactions of polysaccharides with acids. In this case, carbohydrates add acid residues to themselves, resulting in the formation of sulfates, acetates, phosphates, etc. In addition, methanol residues can adhere, which leads to the formation of esters.

Biological role

Polysaccharides in the cell and the body can perform the following functions:

• protective;
• structural;
• stocking;
• energy.

The protective function consists primarily in the fact that the polysaccharides consist of the cell walls of living organisms. So, the cell wall of plants consists of cellulose, fungi - of chitin, bacteria - of murein.

In addition, the protective function of polysaccharides in the human body is expressed in the fact that glands secrete enriched with these carbohydrates, which protect the walls of organs such as the stomach, intestines, esophagus, bronchi, etc. from mechanical damage and the penetration of pathogenic bacteria.

The structural function of polysaccharides in the cell is that they are part of the plasma membrane. They are also components of the membranes of organoids.

The next function is that the main reserve substances of organisms are precisely polysaccharides. For animals and fungi, it is glycogen. In plants, starch is the storage polysaccharide.

The latter function is expressed in the fact that the polysaccharide is an important source of energy for the cell. A cell can get it from such a carbohydrate by splitting it into monosaccharides and further oxidation to carbon dioxide and water. On average, when one gram of polysaccharides is broken down, the cell receives 17.6 kJ of energy.

The use of polysaccharides

These substances are widely used in industry and medicine. Most of them are extracted in laboratories by the polymerization of simple carbohydrates.

The most widely used polysaccharides are starch, cellulose, dextrin, agar-agar.

Now you know what polysaccharides are, what they are used for, what is their role in the body, what physical and chemical properties they possess.