Polysaccharide
In biochemistry, polysaccharides are relatively complex "unsweet" carbohydrates. Polysaccharides are polymers made up of many monosaccharides joined together (hence poly-saccharides). They are therefore very large, often branched, molecules. Properties include insolubility in water and not forming crystals. Examples include starch, cellulose, and glycogen.
Structure
Polysaccharides have the general formula:
- -[Cx(H2O)y)]n-
where y is generally = x - 1.
Starches
Starches are are polymers of glucose. Amylose consists of a linear chain of several hundred of glucose molecules. Amylopectine is a branched molecules made of several thousand of glucose units.
Starches are insoluble in water. They can be digested by hydrolysis done by amylases. Potato, rice, wheat, and maize are major sources of starch in the human diet.
Glycogen
Glycogen is the storage form of glucose in animals. It is a branched polymer of glucose. Glycogen can be broken down to form substrates for respiration, through the process of glycogenolysis. This involves the breaking of most of the C-O-C bonds between the glucose molecules by the addition of a phosphate, rather than a water as in hydrolysis. This process yields phosphorylated glucose molecules, which can be metabolized with a savings of one ATP molecule.
Cellulose
The structural components of plants are formed primarily from cellulose; which humans are unable to digest. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units.