Polysaccharides

More complex sugars are called polysaccharides (from "poly" meaning "many" and "saccharum" meaning "sugar"). Many things in nature are made of polysaccharides. Here we show one of the polysaccharides in corn, another in wood, and another in the exoskeletons of insects like grasshoppers. How are all of these polysaccharides similar? All polysaccharides are composed of long chains of monosaccharides. The monosaccharides are called monomers (from "mono" meaning "one" and "mer" meaning "part"). Although the polysaccharides all look very similar, the bonds between the monosaccharide molecules make them chemically different and allow them to be used for different purposes. Starch is an energy-storage polysaccharide found in plants. The bonds of the polysaccharide can be broken to produce glucose molecules, which the plant can use for energy. Cellulose is a structural polysaccharide found in the cell walls of plants. Cellulose is also composed of glucose monomers, but the bonds between the glucose monomers are different than the bonds in starch. Many organisms, including humans, cannot break the bonds between the glucose monomers of cellulose. Chitin, another structural polysaccharide, is used in the exoskeleton of arthropods. Chitin is very similar to cellulose, but with a nitrogen-containing appendage on each glucose monomer.

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