A polysaccharide is a kind of carbohydrate and it is a polymer composed of chains of monosaccharides linked together by glycosidic linkages. Glycans are another name for polysaccharides. A polysaccharide is described as having more than ten monosaccharide units, whereas an oligosaccharide has three to ten linked monosaccharides.
Polysaccharides can be straight or branched. Linear polysaccharides, like cellulose in trees, can form rigid polymers. Branched forms, such as gum arabic, are frequently soluble in water. Polysaccharide-derived products are available for ion exchange, gel permeation or gel filtration, affinity and conventional chromatographies, gel media for microbial cultures, electrophoresis, and other applications.
Polysaccharides serve three primary functions including, structural support, energy storage, and the transmission of cellular communication signals. The function of a carbohydrate is largely determined by its structure. Linear molecules are strong and rigid, such as cellulose and chitin.
Plants rely on cellulose as their primary support molecule, whereas fungi and insects rely on chitin. Polysaccharides that are being used for energy storage are typically branched and folded upon themselves. They are usually insoluble in water due to their high concentration of hydrogen bonds.
The storage polysaccharides comprises starch in plants and glycogen in animals. Polysaccharides that are used in cellular communication are frequently covalently bonded to lipids or proteins, resulting in glycoconjugates. The carbohydrate acts as a tag, assisting the signal in reaching its intended destination.
Glycoproteins, peptidoglycans, glycosides, and glycolipids are examples of glycoconjugates. Plasma proteins, for instance, are glycoproteins. Let us now understand the importance of polysaccharides below:
What is the importance of polysaccharides like starch, cellulose and glycogen? Starch is one among the significant important dietary sources for humans, as well as one of the primary plant storage polysaccharides. Cereals, roots, and some vegetables contain a high concentration of starch.
It is a -glucose polymer that primarily consists of two components: amylose and amylopectin. Amylose is the most soluble in water and contains about 15-20% starch. Amylose is a long unbranched chain with α-D+ glucose units that range from 200 to 1000 in number and are linked by a C1-C4 glycosidic linkage.
Amylopectin contains about 80-85 percent starch, but it is not soluble in water. This is a branched-chain polymer established by C1-C4 linkage followed by C1-C6 glycosidic linkage.
Cellulose is one of most popular organic substances found in the plant kingdom and it is one of the most significant components of plant cells. These are polysaccharides that form a straight chain and are made up of only β-D-glucose units joined by a glycosidic linkage between the first carbon of the glucose unit and the fourth carbon of the next glucose unit.
Carbohydrates are stored in the body of an animal as Glycogen. It is also recognised as animal starch because its structure is similar to amylopectin and has many branches. It can be found in the liver, muscles, and the brain. When the body requires glucose, the enzymes convert glycogen into glucose. Glycogen can also be found in yeast and fungi.
Arabinoxylans seem to be copolymers of two sugars, arabinose and xylose, and are found in both primary and secondary cell walls of plants and they might be useful to human health.
In fact, plants’ structural components are primarily composed of cellulose. Wood is mostly cellulose and lignin, whereas paper and cotton are almost entirely cellulose. Cellulose is a polymer composed of repeated glucose units held together by beta-links.
Because humans and many animals lack the enzyme required to break the beta-linkages, cellulose cannot be digested. Termites, for example, can digest cellulose because bacteria containing the enzyme are present in their gut. Water does not dissolve cellulose.
When mixed with iodine, it does not change colour. It produces glucose when hydrolyzed. It is the most common carbohydrate found in nature.
Chitin is just one of many polymers found in nature. Many animals, such as exoskeletons, have it as a structural component. It biodegrades in the natural environment over time. Its decomposition may be catalysed by chitinases, which are secreted by microorganisms such as bacteria and fungi and produced by some plants.
A few of these microorganisms have receptors for simple sugars derived from chitin decomposition. If chitin is detected, enzymes are produced to digest it by cleaving glycosidic bonds and converting it to simple sugars and ammonia.
Pectins are indeed a complex polysaccharide family with 1,4-linked -d-galactosyl uronic acid residues. They can be found in most primary cell walls as well as nonwoody parts of terrestrial plants.
Polysaccharides are being used as demulcents, in drug formulations, dental impression materials, dusting powders, hemostatics, and to treat mild intestinal disorders. They are often used as plasma substitutes as well as anticoagulants in solution and as a surface treatment on artificial organs.
Polysaccharides seem to be abundant natural polymers found in plants, animals, and microorganisms. They have exceptional properties and play critical roles in the maintenance of life. They are quite well known for their high nutritive value as well as their beneficial effects on our immune, digestive, and detoxification systems.
They all seem to be good energy sources because they can be quickly digested to simple sugars like glucose, enter cell respiration, and be used to make ATP (cell energy).