What is the structure and functions of Polysaccharides? Information on the formulas, types and examples of Polysaccharides.
Polysaccharides, also knowvn as multiple sugars, are large molecules formed by dehydration synthesis of monosaccharide units. Only glucose molecules are present in the structure of polysaccharides, other monosaccharides are not seen. A polysaccharide molecule may contain as many as 10. 000 monosaccharide units. All have the general formula (C6H10O5) n where n shows the number of monosaccharide units in the molecule. They are less soluble in water, and are not sweet in contrary to other carbohydrates.
Starch is made up of glucose units. It is among the storage products of plants. Many foods such as potatoes, rice, bread and paste are rich in starch. The existence of starch can be determined by lugol or iodine solution. Starch produces a dark- blue color with iodine.
Glycogen is also called as “animal starch”. It’s the primary storage form of glucose in the liver and muscles of the animals. It’s like starch but its subunits are more branched than those of starch. Glycogen gives brown color when treated with iodine solution.
Cellulose is the basic structural material for most plants, is a large, linear molecule composed of 3.000 or more glucose units. The bonds between its sugar units are somewhat different from those in starch and glycogen, and seem to be more resistant to hydrolysis.
Cellulose makes up the main structure of cell wall in plant cells, and is found 50% in trees and 98% in cotton fibers. It’s used for a wide variety of commercial purposes including the manufacture of lumber, production of paper from wood, cloth from cotton, photograph films, varnish and some explosives.
Contrary to glycogen and starch, cellulose cannot be digested by human beings because we do not have the molecules required for breaking down cellulose into its glucose subunits. But some animals; because they live a mutual life with some unicellular organisms, benefit from these required molecules that their “guests” produce; therefore they can use cellulose as a food source.
Cellulose is a very resistant molecule, is not dissolved in water and gives no color change when treated with iodine solution.
It’s the support material for the exoskeletons of arthropods (insects, crustaceans). It’s also present in the cell walls of fungi.