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CARBOHYDRATES

CARBOHYDRATES

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CARBOHYDRATES

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  1. CARBOHYDRATES Dr. Madushani Silva (MBBS)North Colombo Teaching Hospital – Ragama

  2. Carbohydrates • Carbohydrates are called carbohydrates because they are essentially hydrates of carbon (i.e. they are composed of carbon and water and have a composition of (CH2O)n.

  3. The major nutritional role of carbohydrates is to provide energy • digestible carbohydrates provide 4 kilocalories per gram. • No single carbohydrate is essential

  4. Photosynthesis: Sun’s energy becomes part of glucose molecule energy Carbon dioxide Water Chlorophyll GLUCOSE 6 CO2 + 6 H20 + energy (sun) C6H12O6 + 6 O2

  5. 120 grams of glucose / day = 480 calories

  6. Types of Carbohydrates • Monosacchrides • Disaccharides Contain 2 monosacchride units • Polysacchrides Contain many monosacchride units

  7. Simple Sugars -

  8. Monosacchrides • Three Carbons = Triose • Four Carbons = Tetrose • Five Carbons = Pentose • Six Carbons = Hexose

  9. Glucose

  10. Fructose

  11. Galactose D-galactose

  12. Disaccharides

  13. LACTOSE INTOLERANCE: Many healthy people, adults and children have the inability to digest lactose. It maybe inherited or acquired and results from a deficiency of the enzyme LACTASE. Lactase is necessary to breakdown lactose to galactose and glucose.

  14. Lactulose • Heated milk (small amounts), mainly synthetic • Not hydrolyzed by intestinal enzymes, but fermented by intestinal bacteria; used as a mild osmotic laxative

  15. Complex carbohydrates • Oligosaccharides • Polysaccharides

  16. Polysaccharides • Homopolysaccrarides • Heteropolysaccarides Pure Congugated

  17. Homopolysaccrarides • Starch • Glycogen • Dietary fiber

  18. Heteropolysaccarides • Pure Pectin Gums Glycosaminoglycans

  19. Conjugated Protein Proteoglycans (Carbo. constitute a major portion ) Glycoproteins (Proteins constitute a major portion) Lipids Glycolipids

  20. Starch • Major storage carbohydrate in higher plants

  21. Starch • Amylose – long straight glucose chains (a1-4) • Amylopectin – branched every 24-30 glc residues (a 1-6) • Provides 80% of dietary calories in humans worldwide

  22. Glycogen G • Major storage carbohydrate in animals G G G G G G G G G G a 1-6 link G G G G a 1-4 link G G G G

  23. also known as animal starch • stored in muscle and liver • complete hydrolysis yields glucose

  24. Long straight glucose chains (a1-4) • Branched every 4-8 glc residues (a 1-6) • More branched than starch • Less osmotic pressure • Easily mobilized G G G G G G G G G G G a 1-6 link G G G G a 1-4 link G G G G

  25. Glycosaminoglycans (mucopolysaccharides) • Linear polymers of repeating disaccharides • Complex carbohydrates containing amino sugars and uronic acids. • Glycosaminoglycans tend to be negatively charged, because of the prevalence of acidic groups.

  26. Glycosaminoglycans • Hyaluronic acid (Glass): lubricants in synovial fluid , eye, cartilage and tendons; hyaluronidase secreted by bacteria — bacteria invasion. Similar enzyme for sperm to penetrate ovum. • Chondroitin sulfate (Cartilage): tensile strength pf cartilage, tendons and ligament, aorta. • Dermatan sulfate (Skin): skin, blood vessel and heart valves. Pliability of skin.

  27. Glycosaminoglycans • Keratan sulfates (horn): cornea, horn, hair, hoof, nails, claws, no uronic acid. • Heparin (liver): made in mast cell- a anticoagulant with highest negative charge density, release to blood, inhibit blood clotting by binding to antithrombin III - bind to and inhibit thrombin, a protease essential to blood clotting.

  28. Proteoglycan • They may be attached to a protein molecule to form a proteoglycan.

  29. Proteoglycan glycosaminoglycansthat are covalently linked to serine residues of specific core proteins.  The glycosaminoglycan chain is synthesized by sequential addition of sugar residues to the core protein.

  30. Dietary fibers

  31. Fibers • Found in food derived from plants • Includes polysaccharides such as cellulose, hemicellulose, pectins, gums and mucilages • Also includes non-polysaccharides such as lignin, cutins and tannins

  32. Fibers • Fibers are not a source of energy because Human digestive enzymes cannot break down fibers • The bacteria in human GI tract can breakdown some fibers.

  33. classification of fibers based on their solubilities in water • Soluble fibers • Insoluble fibers

  34. classification of fibers based on their solubilities in water (1)Soluble fibers: includes gum,pectin, some hemicellulose and mucilages found in fruits, oats, barley and legumes .

  35. Soluble fibers Actions on body: (i) Delay GI transit(benefits digestive disorders) (ii) Delay glucose absorption (benefits diabetes) (iii) Lowers blood cholesterol(benefits heart disease)

  36. classification of fibers based on their solubilities in water (2) Insoluble fibers: includes cellulose, many hemicellulose, lignin found in wheat bran , corn bran, whole grain bread, cereals and vegetables (carrot, cabbage)

  37. Insoluble fibers Actions in body: (i)Accelerates GI transit and increases fecal weight(promotes bowel movement) (ii) Slows starch hydrolysis and delays glucose absorption(Benefits diabetes)

  38. 2005 Dietary Guidelines for Americans Recommends… “ Consume 3 or more servings (or oz. equivalents) of whole-grain products per day, with the rest of the recommended grains coming from enriched or whole-grain products. In general, at least half the grains should come fromwhole grains.”

  39. Exercise…… • Comment on the importance of dietary fibers in the example shown by the picture below

  40. Dietary carbohydrates • Starch • Sucrose • Glucose and fructose • Lactose • Cellulose • Other plant polysaccharides Digestible Non-digestible by humans

  41. Only monosaccharides are absorbed into the bloodstream from the gut. Digestion of carbohydrates involves their hydrolysis into monosaccharides