Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages and on hydrolysis give the constituent monosaccharides or oligosaccharides. They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose and chitin.
There are two types of polysaccharides: homo-polysaccharides and hetero-polysaccharides. A homo-polysaccharide is defined to have only one type of monosaccharide repeating in the chain; whereas, a hetero-polysaccharide is composed of two or more types of monosaccharides. In both types of polysaccharide, the monosaccharide can link in a linear fashion or they can branch out into complex formations.
Use of Polysaccharides
Polysaccharides have several roles. Polysaccharides such as starch, glycogen, and dextrans are all stored in the liver and muscles to be converted to energy for later use. Amylose and Amylopectin are polysaccharides of starch. Amylose has a linear chain structure made up of hundreds of glucose molecules that is linked by a alpha 1,4 glycosidic linkage. Due to the nature of these alpha 1,4 bonds, the macromolecule often assumes a bent shape. The starch molecules form a hollow helix that is suitable for easy energy access and storage. This gives starch a less fibrous quality and a more granule-like shape which is better suited for storage.
Sources of polysaccharides
Plant foods are natural source of polysaccharides as follows:
Starch is in cereal grains like wheat, oats, rye, barley, buckwheat, rice, etc,
Starch is in potatoes and legumes like beans, peas, lentils.
Fiber is in whole grains like whole-grain bread, brown rice, etc.),
Fiber is legumes, vegetables and fruits.
Functions of polysaccharides
The main functions of polysaccharides are as follows:
Energy storage and
Examples of polysaccharides