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)
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 - we store small amounts in our liver and muscles. Glycogen is broken back down into glucose when energy is needed in a process called glycogenolysis. Research has shown that intense exercise and a high-carbohydrate diet can increase the reserves of glycogen in the muscles and thus may help people exercising work their muscles somewhat longer and harder than normal.
However, cellulose differs greatly from starch in its properties. There are other polysaccharides which effect related compounds and organisms- they are: Callose which is another polymer of glucose found in plants; Inulin which is found in some plants and acts as a storage carbohydrate; Pectins which are found in plant cellulose cell walls; Chitin is similar to the structure of cellulose and is found in fungal hyphae and forms the exoskeleton in arthropods; Murein which is found in the cell walls of bacteria and Mucopolysaccharides found in bone and cartilage. Hence, Polysaccharides are extremely important in plants and animals because they help the organisms to function properly and survive.
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