Polysaccharides: Definition, Structure & Examples - Polysaccharides are carbohydrates containing more than 10 monosaccharides; they function in energy storage and structural support in plants and animals. The way that monomer units are linked together determines the polysaccharide's properties.
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| Polysaccharides structure |
When dehydration synthesis covalently bonds more than 10 monosaccharides together, the result is a macromolecule, sometimes called a polymer. Macromolecules containing monosaccharides are called polysaccharides, meaning many sugars. A polysaccharide may have a branched shape, or it may be arranged like a long linear chain. The chemical properties of polysaccharides are due to the different types of linkages that can occur between the monomer units.
Storage Polysaccharides
Both glycogen (animal starch stored in the liver and muscles of higher animals) and plant starch consist of several hundred glucose units. The two types of polysaccharides react differently because of the way their long chains are arranged. In glycogen, the glucose units are aligned in such a way that they form highly branched forms. In plant starch, the glucose units are aligned to form a twisted, coiled structure. The properties of polysaccharides are due to different types of linkage alignments that can occur between monomer units.
Polysaccharides serve as a means of storing carbohydrates. However, before their elements can be transported through living systems and used for energy, they must undergo hydrolysis and be broken down into monosaccharides or disaccharides. Many times large carbohydrates are formed of only one type of monosaccharide, but some are composed of two, three, or four different types.
Structural Polysaccharides.
Polysaccharides not only function in energy relationships in cells. They are also very important structural components of living things. For example, cellulose, which is made up of glucose monomers, is a fibrous, water-insoluble substance that functions as the main structural material in plant cell walls. In fact, cellulose may well be the most abundant organic chemical in the world. Humans benefit from this abundance, for we use this molecule for such things as lumber, rope fiber, and paper.
Chitin is another polysaccharide, one that is called a modified carbohydrate because it contains nitrogen atoms in its monomer units. Chitin, which is secreted by the outer tissue layer of the animal group that includes lobsters and insects, is the main structural component of the animals' outer skeletons (or exoskeleton). Until recently chitin was thought to have little food value for humans, since humans do not have enzymes to break down this polysaccharide to simpler units. However, biologists now know that some bacteria contain enzymes that can break down chitin into sugars so that the material could be used as a dietary energy source. As a result, some molecular biologists are trying to determine the nature of the gene that controls the production of the enzyme so that we can produce it in large amounts. With this enzyme we can transform the chitin previously believed to be of no use to humans and break it down into sugar.
(Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 59-60)
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