Question

State which types of organism make the following polysaccharides: cellulose, glycogen, chitin, starch. Explain which types are digestible by animals and why

Answer 1

Sol: Cellulose is synthesized by Bacteria to plants, Glycogen synthesized by animals, chitin synthesized by fungi, insects ana starch is synthesized by plants, algae.

Glycogen and starch are digestible by animals because in animals body glycogen is a highly branched, very large polymer of glucose molecules, and glycogen is synthesized from glucose-6- phosphate mainly in the liver and muscle and stored within these tissues as glycogen granules. And animals have enzyme glycogen phosphorylase that break down the glycogen into glucose molecules.

Animals are unable to digest the cellulose because of lacking the cellulase enzyme that break down the beta acetal linkages. And also chitin is not digested by animals because chitin is digested by the enzyme chitinase that lacking in the animals body.

Starch and cellulose are two very similar polymer, in fact they are both made from the same monomer glucose but there is only one difference in starch all the glucose repeat units are oriented in the same direction but in cellulose glucose units it rotated 180 degrees around the axis of the polymer backbone chain. Starch are connected by alpha linkages and glucose unit in cellulose are connected by beta linkages. Our body have enzyme that can break down starch into glucose but cellulose in not, and cellulose is also stronger than starch.