Starch, Glycogen and Cellulose

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Starch: is a polysaccharide, found in many plants in the form of small grains. Large amounts of starch occur in seeds and storage organs. Major source of energy. Starch is made up of a chain of alpha-glucose molecules, linked by glycosidic bonds that are formed in a condensation reaction. Unbranched chain is wound into a tight coil that makes the molecule very compact. The main role of starch is energy storage; it is suited to this because:It is insoluble, so does not draw water into the cells via osmosis. It does not easily diffuse out of cells. Compact, a lot can be stored in one place. When hydrolysed it forms alpha-glucose, which is used in respiration. Glycogen: is a similar structure to starch, but has shorter chains and is more highly branched. Is the major carbohydrate storage product of animals and isMainly stored in small granules in the muscles and liver. Due to small chains it hydrolyses more readily into alpha-glucose. It Suits storage for the same reasons as starch. Cellulose: it is made from monomers of β-glucose. It has straight unbranched chains. Cross linkages form between chains, in the form of hydrogen bonds, this adds little strength. The sheer number of them makes the contribution to strengthening cellulose, making it valuable structural material. The molecules are grouped together to for microfibrils, which are arranged in parallel groups called fibres. Cellulose is a major component of plant cell walls and

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