Give an account of the biological significance of polysaccharides

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Question 8 January 1999

Give an account of the biological significance of polysaccharides (10marks)

Polysaccharides are polymers formed from large amounts of monosaccharide monomers, covalently bonded together by condensation polymerisation.  There are three polysaccharides that commonly effect living organisms: they are Starch, Glycogen and Cellulose.  These polysaccharides play a very significant role in the way plants and animals function.

Starches are polymers of glucose.  There are two common types : (1) amylose, which consists of linear, unbranched chains of several hundred glucose units - the glucose units are linked between their 1 and 4 carbon atoms; (2)  amylopectin, which differs from amylose in being highly, branched - ever so often along the chain, a short side chain is attached to the 6 carbon atoms.

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Starches are biologically significant because they are insoluble in water and can therefore serve as storage areas for glucose. Plants convert excess glucose into starch for storage.  As starch is a common storage compound in plants, it is the main carbohydrate in human diet.  

Animals store excess glucose by polymerising it to form glycogen. The structure of glycogen is similar to that of amylopectin, although the branches in glycogen tend to be shorter and occur more frequently.

Glycogen is biologically significant as we eat relatively small amounts of it and it is used as our main carbohydrate storage compound - ...

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