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Chemistry of carbohydrate for M.B.B.S students


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In detail chemistry of carbohydrate for MBBS students.
Everything explained in detail with biomedical importance and logic behind it.

Published in: Health & Medicine

Chemistry of carbohydrate for M.B.B.S students

  1. 1. Carbohydrate chemistry Dr. Herat D. Soni Assistant professor Rural medical college Loni
  2. 2. Definition Carbohydrates may be defined as polyhydroxy aldehydes or ketones or compounds which produce them on hydrolysis. Formula = (C.H2O)n
  3. 3. Biomedical Importance  Most abundant dietary source of energy. Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source.  Also serve as storage form of energy –Glycogen.  Carbohydrates are precursors for many organic compounds (fats, amino acids).  Participate in the structure of cell membrane & cellular functions (cell growth, adhesion and fertilization).  Certain carbohydrate derivatives are used as drugs, like cardiac glycosides / antibiotics.  DM (diabetes mellitus)
  4. 4. Sources
  6. 6. Classification 1 • Monosaccharide 2 • Oligosaccharide 3 • Polysaccharide
  7. 7. Monosaccharide Cannot further Hydrolyzed
  8. 8. Oligosaccharide • Oligosaccharides(Greek: oligo-few) contain 2-1O monosaccharide molecules • Joined by glycosidic bond
  9. 9. Polysaccharides  Contain more than 10 monosaccharide units.
  10. 10. Polysaccharides Homopolysaccharides Starch Glycogen Cellulose Inulin Dextrans Chitin Heteropolysacchrides Agar Mucopolysaccharide
  11. 11. Isomers  Same chemical formula but different structural formula  Example = Glucose and fructose C6H12O6
  12. 12. Stereoisomer  Same chemical and structural formula but differ in spatial configuration.
  13. 13. Asymmetric carbon atom  Asymmetric carbon means that four different groups are attached to the same carbon.  The reference molecule is glyceraldehyde which has a single asymmetric carbon atom.  The number of possible stereoisomer depends on the number of asymmetric carbon atoms by the formula 2 n where n is the number of asymmetric carbon atoms.
  14. 14. Reference Carbon Atom of Sugars All monosaccharide can be considered as molecules derived from glyceraldehyde by successive addition of carbon atoms. Therefore, penultimate carbon atom is the reference carbon atom for naming the mirror images
  15. 15. D and L isomerism(Enantiomers) • D-sugars are naturally occurring sugars and body can metabolize only D-sugars. • D-glucose is dextrorotatory. In clinical practice, it is often called as dextrose
  16. 16. Optical isomerism(d and l)  The presence of asymmetrical carbon atom causes optical activity. When a beam of plane-polarized light is passed through a solution of carbohydrates, it will rotate the light either to right or to left.  Right = dextrorotatory (+) (d)  Left = levorotatory (-) (l)  D-glucose is dextrorotatory but D-fructose is levorotatory  Equimolecular mixture of optical isomers has no net rotation (racemic mixture)
  17. 17. Epimers  When sugars are different from one another, only in configuration with regard to a single carbon atom, other than the reference carbon atom, they are called Epimers.
  18. 18. Epimers
  19. 19. Anomers To understand this we first understand Three Representations of Glucose Structure
  20. 20. open chain projection formula Fischer's formula Haworth’s formula
  21. 21.  The 1st carbon, aldehyde group is condensed with the hydroxyl group of the 5th carbon to form a ring. Ring structure represents hemi acetal form.  Glucose exists in biological systems not as a rectangle, but as a pyranose ring.  b-D-glucopyranose is the predominant form (63%).
  22. 22.  D-glucose has two anomers, alpha and beta varieties.  These anomers are produced by the spatial configuration with reference to the first carbon atom in aldoses and second carbon atom in ketoses.  These carbon atoms are known as anomeric carbon atoms.
  23. 23. Fischer's formula
  24. 24. Haworth formula Anomeric carbon atom
  25. 25. Mutarotation  When D glucose is crystallized at room temperature, and a fresh solution is prepared, its specific rotation of polarized light is +112o ; but after 12–18 hours it changes to +52.5o .  This change in rotation with time is called mutarotation.
  26. 26. ɑ-D-glucopyranose Rotation of 112 O ɓ-D-glucopyranose Rotation of 19 0 1/3 are alpha type and 2/3rd are beta variety to get the specific rotation of +52.5o Mutarotation
  27. 27. DISACCHARIDES Sucrose Maltose Isomaltose Lactose.
  28. 28. Sucrose • It is the sweetening agent known as cane sugar. • It is present in sugarcane and various fruits.
  29. 29.  Hydrolysis of sucrose (optical rotation +66.5°) will produce one molecule of glucose (+52.5°) and one molecule of fructose (–92°).  Therefore, the products will change the dextrorotation to levorotation, or the plane of rotation is inverted.  Equimolecular mixture of glucose and fructose thus formed is called invert sugar.  The enzyme producing hydrolysis of sucrose is called sucrase or invertase.  Honey contains invert sugar.  Invert sugar is sweeter than sucrose.
  30. 30. Lactose It is the sugar present in milk
  31. 31. Lactose intolerance
  32. 32. Maltose
  33. 33. Isomaltose
  35. 35. Benedict’s test
  36. 36. Principle  The principle of Benedict's test is that when reducing sugars are heated in the presence of an alkali(pH 10.6), they get converted to powerful reducing compounds known as enediols.  Enediols reduce the cupric ions (Cu2+) present in the Benedict's reagent to cuprous ions (Cu+) which get precipitated as insoluble red copper oxide.
  37. 37.  Detect the presence of glucose in urine (glucosuria).  It is a standard laboratory test employed for follow-up of diabetes mellitus in PHC.  Benedict's reagent contains sodium carbonate, copper sulfate and sodium citrate  Any sugar with free aldehyde/keto group will reduce the Benedict's reagent. Therefore, this is not specific for glucose.
  38. 38. Carbohydrates giving positive Benedict ’ s test:  Glucose, Fructose, Galactose  Lactose, Maltose  Sucrose ???????  Starches do not react or react very poorly with Benedict's reagent, due to the relatively small number of reducing sugar moieties, which occur only at the ends of carbohydrate chains.
  39. 39. Non-Carbohydrates giving positive Benedict ’ s test  High concentration of Uric acid and Ketones  Homogentisic acid (solution turns black due to black colored oxidized homogentisic acid)  Vitamin C (even without Boiling)  Certain drugs like aspirin, cephalosporins
  40. 40. Glucose oxidase test  Glucose + O2 Gluconolactone + H2O2  H2O2 + (reduced colourless dye) (Oxidized colored dye) Glucose Oxidase Peroxidase
  41. 41.  Reagents for this test are present on a strip of paper in solid form.  When the paper is wet with urine, the reagents dissolve in urine on paper and react with glucose in urine.  The darkness of color can be correlated with amount of glucose present in urine.  Because Glucose oxidase enzyme can act only on beta-D Glucose, other reducing substances do not give this test positive.
  42. 42.  Thus, compounds like Vitamin C, Aspirin utilize H2O2 produced in the reaction.  Due to lack of H2O2, Peroxidase can not oxidize dye. Thus, glucose may not be detected even if present, if urine contain Vitamin C or Aspirin in large amount. This phenomenon is called false negative result.
  43. 43. Osazone Formation  All reducing sugars will form osazones with excess of phenyl hydrazine when kept at boiling temperature.  Glucose, Galactose and Fructose will produce the same needle-shaped crystals. Why?
  44. 44. Molisch’s test  All carbohydrates when treated with conc. sulphuric acid undergo dehydration to give fufural compounds. These compounds condense with Alpha-napthol to form colored compounds.  Molish test is given by sugars with at least five carbons because it involves furfural derivatives, which are five carbon compounds.
  45. 45. Purple ring at junction
  46. 46. Fehling’s test Same principle as benedicts test Fehling’s A contains 7% copper sulphate and Fehling’s B contains sodium potassium tartarate.
  47. 47. Barfoed’s test  This test is based on the same principle as Benedict’s test.  But, the test medium is acidic.  In acidic medium (pH 4.6) monosaccharides react faster than disaccharide.  Barfoed’s reagent contains copper acetate in glacial acetic acid.
  48. 48. Scanty Red precipitate at bottom of tube
  49. 49. Seliwanoff’s test  Seliwanoff’s test is a chemical test which distinguishes between aldose and ketose sugars.  Ketohexoses like fructose on treatment with HCl form 5- hydroxymethylfurfural, which on condensation with resorcinol gives a cherry red complex.
  50. 50. Cherry red color
  51. 51. Oxidation The glucuronic acid is used by the body for conjugation with insoluble molecules to make them soluble in water for detoxification purpose and also for synthesis of heteropolysaccharides.
  52. 52. Reduction to Form Alcohols  When treated with reducing agents hydrogen can reduce sugars. Aldose yields corresponding alcohol.  Glucose is reduced to sorbitol  mannose to mannitol  fructose becomes sorbitol and mannitol  Galactose is reduced to dulcitol and  ribose to ribitol.
  53. 53. Significance of reduction  Sorbitol, mannitol and dulcitol are used to identify bacterial colonies.  Mannitol is also used to reduce intracranial tension by forced diuresis.  The osmotic effect of sorbitol produces changes in tissues when they accumulate in abnormal amounts, e.g. cataract of lens.
  54. 54. Cataract Retinopathy Nephropathy Neuropathy
  55. 55. Lactulose • Lactulose is also known as beta-D- galactopyranosyl-D-fructofuranose. • Used in constipation
  56. 56. Glycosides  The hydroxyl group of anomeric carbon of a carbohydrate can join with a hydroxyl group of another carbohydrate or some other compound to form a glycoside and the bond so formed is known as glycosidic bond.  eg. R-OH + HO-R’ R-O-R' + H2O  The non-carbohydrate moiety is known as aglycone –phenol, sterol, glycerol and methanol.  Glycosidic bond can be N-linked or, O- linked.
  57. 57. Biomedical importance of glycosides  Cardiac Glycosides –Digoxin, Digitoxin ◦ Used in cardiac insufficiency. ◦ Stimulate cardiac muscle contraction. ◦ Contain steroids as aglycone component.  Ouabain –Sodium pump inhibitor.
  58. 58.  Streptomycin ◦ Antibiotic ◦ Given in Tuberculosis  Phloridzin ◦ cause renal damage, glycosuria. ◦ Blocks the transport of sugar across the mucosal cells of small intestine & also renal tubular epithelium.
  59. 59. Formation of Esters  Esterification of alcoholic groups of monosaccharides with phosphoric acid is a common reaction in metabolism.  Examples :Glucose-6-phosphate, and Glucose-1-phosphate.  ATP donates the phosphate moiety.
  60. 60. Amino sugars Amino groups may be substituted for hydroxyl groups of sugars to give rise to amino sugars
  61. 61. Importance Amino sugars Found in Glucosamine Hyaluronic acid, heparin and blood group substances Galactosamine Chondroitin sulphate of cartilage, bone and tendons. Mannosamine constituent of glycoproteins N-acetylglucosamine (GluNac) and N- acetyl galactosamine (GalNac) constituents of glycoproteins, Mucopolysaccharide and cell membrane antigens.
  62. 62. Deoxy Sugars Oxygen of the hydroxyl group may be removed to form Deoxy sugars
  63. 63. • 2-deoxy D-ribose is important part in DNA.
  64. 64. Homopolysaccharides Starch Glycogen Cellulose Inulin Dextrans Chitin
  65. 65. Starch  It is the reserve carbohydrate of plant kingdom  Sources: Potatoes, cereals (rice, wheat) and other food grains.  Starch is composed of amylose and amylopectin.
  66. 66.  Amylose is made up of glucose units with alpha-1,4 glycosidic linkages to form an unbranched long chain. Water soluble.  The insoluble part absorbs water and forms paste like gel; this is called amylopectin.  Amylopectin is also made up of glucose units, but is highly branched. The branching points are made by alpha-1,6 linkage
  67. 67. Iodine test for starch  Starch will form a blue colored complex with iodine; this color disappears on heating and reappears when cooled. This is a sensitive test for starch.  Starch is nonreducing because the free sugar groups are negligible in number.
  68. 68. Hydrolysis of starch  Amylodextrin = violet color with iodine and is non-reducing.  Erythrodextrin = red color with iodine and mildly reduce the Benedict's solution.  Achrodextrins = no color with iodine, reducing)  Maltose = (no color with iodine, but powerfully reducing) Short time to long time
  69. 69. Glycogen
  70. 70.  It is the reserve carbohydrate in animals. It is stored in liver and muscle.  Liver glycogen stores increase during the well-fed state , and are depleted during a fast.  Glycogen is composed of glucose units joined by alpha-1,4 links in straight chains. It also has alpha-1,6 glycosidic linkages at the branching points.  Glycogen is more branched and more compact than amylopectin.
  71. 71. Liver and muscle glycogen
  72. 72. Cellulose  It is made up of glucose units combined with beta-1,4 linkages.  It has a straight line structure, with no branching points.  Beta-1,4 bridges are hydrolyzed by the enzyme cellobiase. But this enzyme is absent in animal and human digestive system, and hence cellulose cannot be digested.
  73. 73. Importance Fiber can absorb 10–15 times its own weight in water, drawing fluid into the lumen of the intestine Increasing bowel motility 1.Decrease the risk for constipation It is a major constituent of fiber, the nondigestable carbohydrate.
  74. 74. Intestine Bile salt Fibers Excreted Cholesterol Decreases serum cholesterol level . 2. Lower LDL cholesterol levels
  75. 75. Delays gastric emptying and can result in a sensation of fullness 4. Reduced peaks of blood glucose following a meal Can bind various toxic substances including carcinogens & eliminate them in faecal matter 3.Decreases chances of some cancers
  76. 76. Inulin  It is a long chain homoglycan composed of D-fructose units with repeating beta-1,2 linkages.  It is the reserve carbohydrate present in various bulbs and tubers, such as onion, garlic.  It is clinically used to find renal clearance value and glomerular filtration rate.
  77. 77. Dextrans  These are highly branched homopolymers of glucose units with 1-6, 1-4 and 1-3 linkages. They are produced by micro- organisms.  Since they will not easily go out of vascular compartment, they are used for intravenous infusion as plasma volume expander for treatment of hypovolemic shock.
  78. 78. Dextrose, Dextrin and Dextran are different  D-glucose is otherwise called Dextrose, a term often used in bed-side medicine, e.g. dextrose drip.  Dextrin is the partially digested product of starch.  Dextran is high molecular weight carbohydrate, synthesized by bacteria.
  79. 79. Chitin  It is present in exoskeletons of insects.  It is composed of units of N- acetylglucosamine with beta-1,4 glycosidic linkages.
  80. 80. Heteropolysaccharides • Agar • Mucopolysaccharide
  81. 81. Agar  Agar = The linear polysaccharide Agarose + agaropectin  It is dissolved in water at 100ºC, which upon cooling sets into a gel. Agarose is used as matrix for electrophoresis.  Agar cannot be digested by bacteria and hence used widely as a supporting agent to culture bacterial colonies.
  82. 82. Mucopolysaccharide i.e. glycosaminoglycans(GAGs)  [acidic sugar–amino sugar]n.
  83. 83.  Because of their large number of negative charges, these heteropolysaccharide chains tend to be extended in solution. They repel each other, and are surrounded by a shell of water molecules. When brought together, they “slip” past each other.  This produces the “slippery” consistency of mucous secretions and synovial fluid.
  84. 84. This property contributes to the resilience of synovial fluid and the vitreous humor of the eye
  85. 85. GAGs Composition Tissue distribution Functions Hyaluronic acid D-glucuronic acid and N-acetyl D- glucosamine Connective tissue Synovial fluid Vitreous humor Gel around ovum lubricant and shock absorbant in joints Chondroitin sulphate D-glucuronic acid and N- acetyl D-galactosamine 4-sulfate. bone, cartilage, Tendons,heart valves and skin. Helps to maintain the structure And shapes of tissues Dermatan sulfate D-Iduronic acid and N-acetyl D-galactosamine 4 –sulfate. Skin Helps to maintain shapes of tissues Keratan sulphate galactose and N-acetyl glucosamine cornea tendons Keeps cornea Transparent Heparin sulphated glucosamine and glucuronic acid or iduronic acid blood, lung, liver ,kidney, spleen Anticoagulant Clearing factor
  86. 86. Hyaluronic acid N-Acetyl-glucosamine → beta-1, 4- Glucuronic acid → beta-1-3-N-Acetyl glucosamine and so on.
  87. 87. Hyaluronidase Breaks b(1-4 linkages) in hyaluronic acid. Present in high concentration in testes, seminal fluid, and in certain snake and insect venoms. Hyaluronidase of semen clears the gel (hyaluronic acid) around the ovum allowing a better penetration of sperm into the ovum. Serves important role in fertilization Hyaluronidase of bacteria helps their invasion into the animal tissues.
  88. 88. Chondroitin sulphate glucuronic acid → beta-1,3-N-acetyl galactosamine sulfate → beta-1, 4 and so on
  89. 89. Dermatan sulfateDermatan sulfate L-iduronic acid and N-acetylgalactosamine in beta-1, 3 linkages
  90. 90. Keratan sulphate  Only GAG not having Uronic acid.
  91. 91. Heparin It contains repeating units of sulphated glucosamine → alpha-1, 4-L-iduronic acid or glucuronic acid → and so on
  92. 92.  Heparin is an anticoagulant( prevents blood clotting).  Heparin helps in the release of the enzyme lipoprotein lipase which helps in clearing the turbidity of lipemic plasma.  Lipoprotein lipase breaks TG in glycerol and FFA.
  93. 93. HSEN Heparan sulphate Capillary On capillary endothelial wall surface Lipoprotein lipase Heparin displaces lipoprotein lipase from heparan sulphate binding site hence clearing factor
  94. 94. Proteoglycans and Glycoproteins  Proteoglycans: When carbohydrate chains are attached to a polypeptide chain.  Glycoproteins: Carbohydrate content ≤ 10%.
  95. 95. Proteoglycans Figure showing Proteoglycans aggregate
  96. 96. Glycoprotein Major function Glycophorin glycoprotein of erythrocytes cell membrane Collagen Structure of cartilage and bone Ceruloplasmin Transport protein Immunoglobulin Defense against infection Intrinsic factor Absorption of vitamin B12 Fibrinogen Blood clotting
  97. 97. Thank you Any questions?