Polysaccharide

Cellulose I_ structure

Amylose 3D projection

Glycogen structure

Glycogen space-filling model

Structural polysaccharides

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. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their monosaccharide building blocks. They may be amorphous or even insoluble in water.

Structure and Properties

Polysaccharides are long chains of monosaccharides linked by glycosidic bonds. Three important polysaccharides, starch, glycogen, and cellulose, are composed of glucose. Starch and glycogen are used by plants and animals, respectively, to store energy, while cellulose is used by plants for structural purposes.

Functions

Polysaccharides have a general formula of C_n(H₂O)_n-1 where n is usually a large number between 200 and 2500. Considering that the polysaccharides are very large macromolecules, they have a mass of up to several million Daltons. They are very complex, having branches off of their main chain.

Types of Polysaccharides

There are various types of polysaccharides. Among these are:

• Starch: A polymer of glucose found in roots, tubers and seeds of plants.
• Glycogen: The storage form of glucose in animals and humans which is analogous to the starch in plants.
• Cellulose: A polysaccharide consisting of glucose monomers that reinforces the cell walls of plants.
• Chitin: A polymer of N-acetylglucosamine, a derivative of glucose, which is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans and insects, and the radulas of mollusks.

See Also

• Monosaccharide
• Disaccharide
• Oligosaccharide