Dr.S.Chakravarty , MD

1. I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit Nature and more time tasting her sweetnessand respecting her seniority. —E. B. White, “Coon Tree,” 1977

2. Dr.S.Chakravarty, MD Chemistry of Carbohydrates

3. CARBOHYDRATES !!! WHAT COMES TO YOUR MIND ??

4. Each year , 100 metric tons of CO2 is converted to Carbohydrates by plants…..

5. “Hydrates of Carbon” Polyhydroxyaldehydes or ketones or compounds which yield them on hydrolysis. • General molecular formula Cn (H2O)n -Some carbohydrates contain Sulphur , Nitrogen or Phosphorus Exceptions are acetic acid C2H4O2 and lactic acid C3H6O3 . Rhamnose C6H12O5 is a carbohydrate

6. Functions of Carbohydrates • Main sources of ENERGY in body (4kcal/g) • RBCs and Brain cells have an absolute requirement of carbohydrates . • Storage form of energy (starch and glycogen) • Excess carbohydrate is converted to fat. • Glycoproteins and glycolipids are components of cell membranes and receptors. • Structural basis of many organisms .e.g . Cellulose in plants ,exoskeleton of insects , cell wall of microbes, mucopolysaccharides and ground substance in higher organisms.

7. Glycobiology & Sugar Code of Life Oligosaccharide Chains Encode Biologic Information --An enormous number of glycosidic linkages can be generated between sugars. For example, three different hexoses may be linked to each other to form over 1000 different trisaccharides. --Oligosaccharide chains encode biologic information and that this depends upon their constituent sugars, their sequences, and their linkages. For instance, mannose 6-phosphate residues target newly synthesized lysosomal enzymes to that organelle (see later). --The biologic information that sugars contain is expressed via interactions between specific sugars, either free or in glycoconjugates, and proteins (such as lectins; see below) or other molecules These interactions lead to changes of cellular activity.

8. Classification of Carbohydrates Carbohydrates Monosaccharides 1 sugar unit Disaccharides 2 sugar units Oligosaccharides 3-9 units Polysaccharides >10 e.g.Glucose , fructose etc e.g.Sucrose e.g. Maltotriose Homoglycans Heteroglycans e.g. starch, glycogen e.g. GAGs or glycosaminoglycans

9. Monosaccharides • Molecules having only one actual or potential sugar group .

10. Pentoses of Physiological importance

11. Hexoses of Physiological Importance

12. Enediol formation :- • In mild alkaline solutions, carbohydrates containing a free sugar group (aldehyde or ketone) will tautomerise to form enediols , where two hydroxyl groups are attached to the double-bonded carbon atoms . • Since enediols are powerful reducing agents in alkaline medium. When oxidising agents like cupric ions are present , sugars form a mixture of carboxylic acids by breaking at the double bonds.

14. BENEDICT’S AND FELHING’S TEST BENEDICT’S REAGENT :- Sodium carbonate , copper sulphate , sodium citrate Principle:- In alkaline medium , sugars form enediols , cupric ions are reduced , correspondingly the sugar is oxidized . Reducing sugar :- Any sugar with a free aldehyde or ketone grp. is a reducing sugar. Clinical application :- Benedict’s test is a bed side test for detection of reducing sugar in urine(Clinitest, Urine)

15. Clinitest, Urine Benedict’s test Procedure: - 0.5 (8 drops)ml urine + 5ml Benedict’s reagent . Boil for 2 mins. Interpretation:- Drawback – test is not specific for glucose Fehling’s test :- no intermediate colors are formed as because over there a powerful reducing agent KOH is used.

16. Osazone formation • All reducing sugars will form osazones with excess of phenylhydrazine when kept at boiling temperature. • Osazones are insoluble . • Osazones of individual sugars have characteristic crystal from .The differences in glucose , fructose and mannose are dependent on 1st and 2nd C & this difference is masked when Phenyhydrazine reacts with these two carbons . So, Glucose , Fructose and Mannose give broom shaped osazones.

17. Osazones –CHARACTERISTIC STRUCTURES Glucosazone ( broom shaped) Maltosazone ( star shaped) Lactosazone (powder puff shaped)

18. 4)Reduction to form alcohols When treated with reducing agents such as sodium amalgam, hydrogen can reduce sugars . Aldose yields corresponding alcohol .Ketoses form two alcohols because of appearance of new asymmetric carbon in this process. E.g. D-Glucose  D-Sorbitol  D-Fructose  D-Mannitol Sorbitol and Mannitol are used to identify bacterial bacterial colonies. Mannitol is used to reduce intracranial pressure by forced diuresis. The osmotic effect of sorbitol and dulcitolproduces changes in tissues when they accumulate in abnormal amounts. E.g cataract

19. Ketoses forms two alcohols because of appearance of asymmetric carbon atoms in this process. D-fructose D-glucose Galactose Dulcitol and Ribose Ribitol

20. Glycosides • When the hemi-acetal group (hydroxyl grp of the anomeric C ) of a monosaccharide is condensed with an alcohol or phenol grp , it is called as a glycoside .The non-carbohydrate grp is called aglycone. • Glycosides are non –reducing (WHY ?)but they may be hydrolyzed by boiling with dilute acids. • - glycosides are hydrolyzed by maltase from yeast , while beta-glycosides are hydrolyzed by Emulsin from almonds .So enzyme hydrolysis affords a method to distinguish b/w two forms .

22. Some important Glycosides

23. Disaccharides • When 2 monosaccharides are combined together by glycosidic linkage , a disaccharide is formed. • Two types :- Non-reducing Sucrose Cane sugar Trehalose in yeast Reducing Lactose Milk sugar Maltose Malt sugar

24. Sucrose • Cane sugar, table sugar • Glu + Fru (β12) • Sweetening agent • Non-reducing • No osazones • Clinical Importance :- --dental caries --Bypasses metabolic check points- OBESITY --“Sucrase deficiency “

25. Lactose • Milk sugar • Gal + Glu(β14) • Reducing • Beta glycosidic linkage • Osazone – Powder Puff or hedgehog shaped

26. Lactose Intolerance • Deficiency of enzyme lactase in brush border epithelium • Primary – only in adults , absence of a lactase persistence allele • Congenital- children( autosomal recessive) • Secondary - Also common in acute gastroenteritis , Abdominal cramps , pain , distension and diarrhoea. Treatment :- Restriction of dairy products Soy milk can be used for children

27. Maltose • 2 glucose residues( 1 4 linkage) • Reducing • Malt sugar • Osazone :- Star shaped or flower petal shaped

28. Lactulose • Synthetic disaccharide of Galactose and Fructose • Poorly absorbed from the gastrointestinal tract • Used in the treatment of hepatic encephalopathy • Metabolized by the colonic bacteria to acidic products CAUSES PURGATION • Promotes the excretion of ammonia in feces as protonated ammonium ions

29. Polysaccharides HETEROGLYCAN OR HETEROPOLYSACCHARIDE HOMOGLYCAN OR HOMOPOLYSACCHARIDE

31. HOMOGLYCANS • STARCH • GLYCOGEN • CELLULOSE • INULIN • DEXTRANS • CHITIN

32. STARCH • Carbohydrates of the plant kingdom • Sources :- Potatoes , tapioca, cereals (rice , wheat) and other food grains • Composed of AMYLOSE & AMYLOPECTIN AMYLOSE :- When starch is treated with boiling water , 10 -20 % is solubilized ; This part is called amylose .Contains glucose units with -1,4 glycosidic linkages .Mol wt =400,000 or more AMYLOPECTIN :- the insoluble part absorbs water and forms paste like gel ; this is called as amylopectin. Amylopectin is also made up of glucose units , but is highly branched with molecular weight more than 1 million. The branching points are made by - 1, 6 linkage

34. Starch

35. GLYCOGEN • Storage form of energy in animal. • Stored in liver and muscle . • Stores more glucose residues per gram than starch. • More branched and compact than starch. • Less osmotic pressure. • More energy in a smaller space.

36. Glycogen in liver (6-8%) is higher than that in the muscles (1-2%). • Liver glycogen - first line of defense against declining blood glucose levels especially between meals. Muscle Glycogen –only Locally available to muscles !!

37. A homopolysaccharide - linear chain of (1→4) linked glucosyl residues with branches joined by  (1→6) linkages

38. INULIN • D -fructose chain in -1,2 linkages. • Source :- bulbs and tubers chicory, dahlia, dandelion, onions, garlic. • Not metabolized . • Not absorbed nor secreted by kidneys. • USE – to measure GFR.

39. DEXTRANS • Highly branched homoglycan containing Glu residues in 1-6, 1-4 and 1-3 linkages. • Produced by microbes. • Mol. wt :- 1-4 million. • Colloidal solution, Low osmotic effects, slow disintegration and utilization, slow elimination from the body • As large sized , they will not move out of vascular compartment so used as plasma expanders. • In hypovolemic shock, given intravenously increases blood volume.

40. Heteroglycans

41. Mucopolysaccharides or GAG --- [ URONIC ACID + AMINO SUGAR]---n Acetylated amino sugars, sulfate and carboxyl groups may also be present

42. Amino sugars • Amino grps. may be substituted for hydroxyl grps of sugars to give rise to amino sugar. • Generally the grp is added to the second C of hexoses. • They are non –reducing and do not form osazones • They are found in GAGS , glycoproteins , proteoglycans • Abbreviations :- GluNac = N-acetyl –glucosamine GalNac =N-acetyl-galactosamine GLUCOSAMINE or 2 amino-D-glucopyranose (α form)

43. The amino group may be further acetylated to produce N-acetlyated sugars like N-acetly glucosamine (GlcNac) or N-acetyl galactosamine(GalNac) which are important constituents of glycoproteins and MPS

45. Chondroitin sulfate Dermatan sulfate Wide distribution in ECM Iduronic acid + N-actylgalactosamine sulfate. Helps in wound repair and fibrosis. • Most abundant • glucuronic acid + N-acetyl galactosamine sulfate • Found in cartilage, tendon, ligament. • provides much of the resistance of cartilage to compression.

46. Keratan sulfate Heparin Sulfated iduronic acid + sulfated glucosamine Found in mast cells Acts as an anticoagulantbindsantithrombin III and activates it • N-acetyl glucosamine and galactose • Absence of glucuronic acid. • Very heterogenous molecules – have additional groups – NANA, mannose etc. • KSI –CORNEA • KS II – Loose connective tissue

47. Heparan sulfate Hyaluronic acid glucuronicacid + N-acetyl glucosamine Not sulfated Not linked to any protein Found in synovial fluid of joints, vitreous humor of eye. • Glucuronic acid + Glucosamine • They are acetylated compared to heparin. • Found in basement membrane and cell surface, Skin fibroblasts and aortic walls

48. Relationship between GAG structure and function • strong negative charges -- > ( POLYANIONS )(-COO- and -OSO3-) cause molecule to fan outwards and repel adjacent molecules • Surrounded by a shell of hydration. • Slippery consistency – similar to magnets. • Act like cushions – compressible but spring back after the pressure is removed (sponge effect).

49. RESILIENCE of GAGS • reversible compressibility accounts for resilience of synovial fluid and vitreous humor of eye.

50. Some Functions of Glycosaminoglycans and Proteoglycans