POLYSACCHARIDE

'Polysaccharides' are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic linkages. They are therefore very large, often branched, macromolecules. They tend to be amorphous, insoluble in water, and have no sweet taste.
When all the constituent monosaccharides are of the same type they are termed ''homopolysaccharides''; when more than one type of monosaccharide is present they are termed ''heteropolysaccharides''.
Examples include storage polysaccharides such as starch and glycogen and structural polysaccharides such as cellulose and chitin.
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 repeating units in the polymer backbone are often six-carbon monosaccharides, the general formula can also be represented as (C₆H₁₀O₅)_n where n=40-3000.

Contents

Storage polysaccharides

Starches

Structural polysaccharides

Cellulose

Acidic polysaccharides

Bacterial capsule polysaccharides

See also

External links

Storage polysaccharides

Starches

Starches are glucose polymers in which glucopyranose units are bonded by ''alpha-''linkages. It is made up of a mixture of Amylose and Amylopectin. Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units.

Starches are insoluble in water. They can be digested by hydrolysis, catalyzed by enzymes called amylases, which can break the ''alpha-''linkages. Humans and other animals have amylases, so they can digest starches. Potato, rice, wheat, and maize are major sources of starch in the human diet.

Structural polysaccharides

Cellulose

The structural components of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units bonded together by ''beta-''linkages. Humans and many other animals lack an enzyme to break the ''beta-''linkages, so they do not digest cellulose. Certain animals can digest cellulose, because bacteria possessing the enzyme are present in their gut. The classic example is the termite.

Acidic polysaccharides

Acidic polysaccharides are polysaccharides that contain carboxyl groups, phosphate groups and/or sulfuric ester groups.

Bacterial capsule polysaccharides

Pathogenic bacteria commonly produce a thick, mucous-like, layer of polysaccharide. This "capsule" cloaks antigenic proteins on the bacterial surface that would otherwise provoke an immune response and thereby lead to the destruction of the bacteria. Capsular polysaccharides are water soluble, commonly acidic, and have molecular weights on the order of 100-1000 kDa. They are linear and consist of regularly repeating subunits of one ~ six monosaccharides. There is enormous structural diversity; nearly two hundred different polysaccharides are produced by E. coli alone. Mixtures of capsular polysaccharides, either conjugated or native are used as vaccines.
Bacteria and many other microbes, including fungi and algae, often secrete polysaccharides as an evolutionary adaptation to help them adhere to surfaces and to prevent them from drying out. Humans have developed some of these polysaccharides into useful products, including xanthan gum, dextran, gellan gum, and pullulan.

See also

★ Polysaccharide encapsulated bacteria

External links

★ Polysaccharide Structure

★ Applications and commercial sources of polysaccharides