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Polysaccharides

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Polysaccharides

  1. 2. <ul><li>Simply known as glycans. </li></ul><ul><li>Consists of repeat units of monosaccharides(hundruds and thousands)or their derivatives held together by glycosidic bonds. </li></ul><ul><li>Linear and branched polymers. </li></ul><ul><li>Homopolysaccharides and hetropolysaccharides </li></ul>
  2. 3. HOMOPOLYSACCHARIDES <ul><li>STARCH. </li></ul><ul><li>Starch is a polymer consisting of D-glucose units. </li></ul><ul><li>Starches (and other glucose polymers) are usually insoluble in water because of the high molecular weight, but they can form thick colloidal suspensions with water. </li></ul>
  3. 4. <ul><li>Main sources of starch are rice, corn, wheat, potatoes. </li></ul><ul><li>A storage polysaccharide in plants. </li></ul><ul><li>It contains two polysaccharide units, amylose and amylopectin . </li></ul>
  4. 5. <ul><li>STARCH –AMYLOSE </li></ul><ul><li>Amylose consists of long unbranched chains of Alpha D-glucose(50-5000 glucose units) connected by glycosidic linkages. </li></ul>
  5. 6. <ul><li>10%-20% of the starch in plants is in this form. </li></ul><ul><li>Water soluble. </li></ul><ul><li>Amylose forms helices (coils) which can trap molecules of iodine, forming a characteristic deep blue-purple color. (Iodine is often used as a test for the presence of starch). </li></ul>
  6. 7. <ul><li>STARCH — AMYLOPECTIN </li></ul><ul><li>Amylopectin consists of long chains of glucose up to 1 million glucose units connected by glycosidic linkages, with branches every 24 to 30 glucose units along the chain. </li></ul><ul><li>80-90% of starch is in this form in plants. </li></ul>
  7. 9. <ul><li>ACTION OF ENZYMES ON STARCH </li></ul><ul><li>The enzymes hydrolyzing starch are called amylases. </li></ul><ul><li>Saliva contains salivary amylase and pancreatic juice contains pancreatic amylase. </li></ul><ul><li>These amylases are α amylases and hydrolyze starch into maltose,isomaltose and α dextrins. </li></ul>
  8. 10. <ul><li>DEXTRINS </li></ul><ul><li>These are immediate products of hydrolysis of starch by acids or by the enzyme amylase. </li></ul><ul><li>Consists of complex mixture of molecules of different sizes and structures. </li></ul><ul><li>Present in the leaves of all starch producing plants. </li></ul><ul><li>Sweet in taste. </li></ul><ul><li>α - dextrins have eight α -D-glucose residues showing mostly glycosidic linkages in addition to an linkage at each of branching site. </li></ul>
  9. 11. Dextrans <ul><li>Products of the reaction of glucose and the enzyme transglucosidase from Leuconostoc mesenteroides. </li></ul><ul><li>contains a (1,4), a (1,6) a (1,3) and a (1,2) linkages. </li></ul><ul><li>MW: 4,000,000 </li></ul>
  10. 12. <ul><li>Used as plasma extenders (treatment of shock). </li></ul><ul><li>Decreases vascular thrombosis . </li></ul><ul><li>Larger dextrans, which do not pass out of the vessels, are potent osmotic agents, and thus have been used urgently to treat hypovolemia . </li></ul><ul><li>The hemodilution caused by volume expansion with dextran use improves blood flow. </li></ul>
  11. 13. <ul><li>Intravenous solutions with dextran function both as volume expanders and means of nutrition . Such a solution provides an osmotically neutral fluid that once in the body is digested by cells into glucose and free water. </li></ul><ul><li>It is occasionally used to replace lost blood in emergency situations, when replacement blood is not available. </li></ul>
  12. 14. <ul><li>It is used in some eye drops as a lubricant. </li></ul><ul><li>also used as molecular sieves to separate proteins and other large molecules (gel filtration chromatography) </li></ul><ul><li>component of dental plaques. </li></ul>
  13. 15. Glycogen <ul><li>Also known as animal starch. </li></ul><ul><li>Stored in muscle and liver (mostly). </li></ul><ul><li>Present in cells as granules (high MW). </li></ul><ul><li>Contains both a(1,4) links and a(1,6) branches at every 12-14glucose unit (more frequent than in starch). </li></ul>
  14. 16. <ul><li>CELLULOSE </li></ul><ul><li>A polymer consisting of long, unbranched chains of D-glucose connected by </li></ul><ul><li>glycosidic linkages,may contain from </li></ul><ul><li>15000 glucose units in one molecule. </li></ul>
  15. 18. <ul><li>HEMICELLULOSE </li></ul><ul><li>Group of high molecular weight carbohydrates that resemble cellulose,but are more soluble and easily decomposed. </li></ul><ul><li>besides glucose, sugar monomers in hemicellulose can include xylose , mannose , galactose , rhamnose , and arabinose . </li></ul><ul><li>Hemicelluloses contain most of the D- pentose sugars, and occasionally small amounts of L-sugars as well. </li></ul><ul><li>Xylose is always the sugar monomer present in the largest amount </li></ul>
  16. 19. Chitin <ul><li>chitin is the second most abundant carbohydrate polymer </li></ul><ul><li>Like cellulose, chitin is a structural polymer </li></ul><ul><li>present in the cell wall of fungi and in the exoskeletons of crustaceans, insects and spiders </li></ul><ul><li>Consists of N-acetyl-D-glucosamine units joined by </li></ul>
  17. 20. Inulin <ul><li> -(1,2) linked fructofuranoses </li></ul><ul><li>linear only; no branching </li></ul><ul><li>lower molecular weight than starch </li></ul><ul><li>hydrolysis yields fructose </li></ul><ul><li>sources include onions, garlic etc. </li></ul><ul><li>used as diagnostic agent for the evaluation of glomerular filtration rate (renal function test) </li></ul>

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