polysaccharide

Definition: Polysaccharides are to be polymers of monosaccharides containing ten or more monosaccharide residues.

Polysaccharides are polymeric carbohydrate structures, formed of repeating units (either monosaccharides or disaccharides) joined together by glycosidic bonds.

These structures are often linear, but may contain various degrees of branching. 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.

When all the monosaccharides in a polysaccharide are the same type the polysaccharide is called a homopolysaccharide, but when more than one type of monosaccharide is present they are called heteropolysaccharides.

Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose and chitin.

Polysaccharides have a general formula of Cx(H2O)y where x is usually a large number between 200 and 2500. Considering that the repeating units in the polymer backbone are often six-carbon monosaccharides, the general formula can also be represented as (C6H10O5)n where 40≤n≤3000

Nomenclature

Polysaccharides have been given trivial names that reflect their origin. Two common examples are cellulose, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to stiffen.

To name a polysaccharide composed of a single type of monosaccharide, that is a homopolysaccharide, the ending “-ose” of the monosaccharide is replaced with “-an”.

For example, a glucose polymer is named glucan, a mannose polymer is named mannan, and a galactose polymer is named galactan. When the glycosidic linkages and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration.

See also

 glycogen