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CARBOHYDRATES POLYSACCHARIDES

MS1005N General Biochemistry. CARBOHYDRATES POLYSACCHARIDES. Dr Sundus Tewfik s.tewfik@londonmet.ac.uk. 32. Divided into homopolysaccharides - only one type of monomer eg all glucose or heteropolysaccharides - with 2 or more different types of monomer

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CARBOHYDRATES POLYSACCHARIDES

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  1. MS1005N General Biochemistry CARBOHYDRATES POLYSACCHARIDES Dr Sundus Tewfik s.tewfik@londonmet.ac.uk

  2. 32. Divided into homopolysaccharides - only one type of monomer eg all glucose or heteropolysaccharides - with 2 or more different types of monomer eg starch has only D-glucose thus it is a homo-polysaccharide,

  3. whereas hyaluronic acid has alternating units of D-glucuronic acid and N-acetyl D-glucosamine.

  4. Homopolysaccharides may be given class names, if one contains glucose it is called a glucan, if one contains mannose it is called a mannan.

  5. -amylose 33. Storage polysaccs. are deposited as large granules in cytoplasm: starch in plants and glycogen in animals 34. Starch occurs in 2 forms, α-amylose and amylopectin. amylopectin

  6. α-amylose consists of long unbranched chains in which all D-glucose units are in α(14) linkages. The chains vary in Mr from a few thousand to ~500,000.

  7. amylopectin is highly branched with branch points occurring every 12 glucose units. The chains have α(14) linkages but the branch points are α(16) linkages. Its Mr may be as high as 1,000,000.

  8. 35. >50% carbohydrate ingested by humans is starch. Both amylose and amylopectin are rapidly hydrolysed by α-amylase. This enzyme hydrolyses internal α(14) linkages to yield maltose, maltotriose and α-dextrin.

  9. maltotriose

  10. 36. Glycogen is abundant in muscle and liver, it is a polysacc. of D-glucose in α(14) linkages. It is branched every 8-10 glucose units (ie more branched than amylopectin)

  11. 37. Structural polysaccs. Cellulose is the most abundant organic compound in the biosphere. Wood ~50% cellulose, cotton ~100% cellulose. All the linkages in cellulose are β(14). Most animals do not have enzymes capable of hydrolysing these linkages, so cellulose not used as nutrient. Some animals such as cows which have cellulases in the rumen capable of hydrolysing cellulose to D-glucose.

  12. cellulose Every other glucose is flipped over, due to β linkages. This promotes intra-chain and inter-chain H-bonds andvan der Waals interactions, that cause cellulose chains to be straight & rigid, and pack with a crystalline arrangement in thick bundles - microfibrils

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