Polysacchirides

 Polysaccharides:

         These are tasteless and the most abundant carbohydrates in nature. These are formed by the combination of serval of monosaccharides through glycosidic linkage. These are the most abundant and complex carbohydrates. These are sparingly soluble in water. All polysaccharides are non-reducing sugar. Some polysaccharides are made u of the same type of monosaccharides and are called homopolysaccharides and some polysaccharides are made up of different types of monosaccharides and are called heteropolysaccharides. For example, dextrin, agar, pectin,  chitin, cellulose, starch, and glycogen. Some polysaccharides are explained below:

Starch:

        The main source of carbohydrates for animals is starch. It is present in fruits, seeds, grains, and tubers. Potato tubers are also a rich source of carbohydrates for humans. It is formed by the condensation of hundred of Alpha-glucose. Starch is digested in the oral cavity and in the small intestine by an enzyme called amylase. Plants store food in the form of starch. Upon hydrolysis, it yields first maltose which is further digested by the enzyme maltase to yield glucose. Its presence can be confirmed by the iodine test as it gives blue color with iodine. There are two types of starch:

• Amylose is unbranched and consists of a linear chain of glucose which are attached to each other by alpha-1-4, glycosidic linkage. It is soluble in hot water and not in cold water.
• Amylopectin is branched, a branch of glucose molecules attached to the linear chain through alpha-1-6 glycosidic linkage. It is not soluble in hot water and cold water.

Glycogen:

     It is also a homopolysaccharide made up of alpha glucose. It is also called animal starch. Animals store food in the form of glycogen in all cells but are found abundantly in liver and muscle cells. As the storage carbohydrate of plants is starch, similarly, the storage carbohydrate of animals is glycogen. It is insoluble in water. The structure of the glycogen is similar to amylopectin but it has more branching than amylopectin. The digestion of glycogen is similar to the digestion of starch.  Its presence can be confirmed by the iodine test as it gives a red color with iodine.

Cellulose:

            Cellulose is the most abundant carbohydrate in nature. Cotton and paper are pure forms of cellulose. It is a homoploysaccharides but unlike starch and glycogen, it is formed by the condensation of hundred of beta-glucose by beta-1-4glycosidic linkage. so the beta-1-4glycosidic linkage is most abundant linkage in nature. It is the structural carbohydrate of plants as it is the major constituent of plant cell walls. the structure of cellulose resembles amylose as it has an unbranched structure. It is also insoluble in water and gives no color to iodine. It is not digested in the human digestive system. However, some herbivores have some symbiotic microorganisms like bacteria, protozoa, and yeasts in their digestive tract. These organisms secrete the enzyme cellulase for its digestion. Upon hydrolysis, it first converts into a disaccharide called cellobiose which is further converted into glucose.

Chitin:

      It is the second most abundant carbohydrate in nature. It is also a homopolysaccharide. It is the structural carbohydrate of the fungal cell walls and is found in the exoskeleton of arthropods. It is also called fungal cellulose. It has an unbranched structure and is the derivative of the N-acetyl glucosamine, the modified form of glucose. It is also formed by the condensation of beta glucose.

   

For learning topics of  Oligosaccharides and monosaccharides visit this link:

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