Biomolecules:
Carbohydrates
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In this module:

Introduction
Definition
Linear and Cyclic Forms
Anomers
Disaccharides
Polysaccharides
Variations
Other Functions

Polysaccharides

Polysaccharides are long chains of monosaccharides linked by glycosidic bonds. Three important polysaccharides, starch, glycogen, and cellulose, are composed of glucose. Starch and glycogen serve as short-term energy stores in plants and animals, respectively. The glucose monomers are linked by α glycosidic bonds.

Glycogen and starch are highly branched, as the diagram at right shows. What advantage do you think branching gives to the organism? Type your answer in the space below and click on the Check button.


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The enzymes that build up and break down glycogen and starch act on the free ends of the polysaccharides. Having a great deal of branching ensures that plants and animals can quickly add to their energy supply when energy is plentiful, or break it down the storage molecules when energy is in short supply.

Cellulose is the most abundant organic molecule on earth, since it is the main component of plant cell walls. Wood, paper, and cotton are the most common forms of cellulose. The glucose units in cellulose are linked by β glycosidic bonds, different than the α glycosidic bonds found in glycogen and starch. Cellulose has more hydrogen bonds between adjacent glucose units, both within a chain and between adjacent chains, making it a tougher fiber than glycogen or starch. This is why wood is so tough.

Polysaccharides