Introduction to Carbohydrates and its Chemistry

A Comprehensive Introduction to Carbohydrates its chemistry, classification, qualitative tests an disorders related to its metabolism. This will give readers a overall insight to this topic. All types of queries and suggestions are most welcome

1. DHANANJAY R. PATIL M.PHARMA. (PHARMACEUTICAL CHEMISTRY)

2. - Carbohydrates are the most abundant organic molecules in nature . - Carbo -Hydrates means “ Hydrates of carbon .” also called saccharides , which means “sugars.” - Carbohydrates are defined as polyhydroxyaldehydes or polyhydroxy ketones or compounds which produce them on hydrolysis . - Composed of - carbon Sulphur, Nitrogen or Phosphorus hydrogen oxygen CARBOHYDRATES Life’s Sweet Molecules

3. -They act as storehouses of chemical energy (glucose, starch, glycogen); are the components of supportive structures in plants (cellulose), crustacean shells (chitin) and connective tissues in animals (acidic polysaccharides) and are essential components of nucleic acids (D-ribose and 2-deoxy-D-ribose). -Carbohydrates make up about three fourths of the dry weight of plants. But in animals it is less than 1%. - General molecular formula - C n H 2n O n - Several non-carbohydrates compound are ( acetic acid C 2 H 4 O 2 and lactic acid C 3 H 6 O 3 ) also appear as hydrates of carbon. But, some of genuine carbohydrates ( rhamnohexose C 6 H 12 O 5 and deoxyribose C 5 H 10 O 4 ) do not satisfy the general formula.

4. - Animals get their carbohydrates by eating plants but they do not store much, than they consume. -Carbohydrates are produced by photosynthesis in plants, such as glucose are synthesized in plants from CO 2 , H 2 O, and energy from the sun. Then, are oxidized in living cells to produce CO 2 , H 2 O, and energy.

5. Each year, 100 metric tons of CO 2 is converted to Carbohydrates by plants

6. Carbohydrates Disaccharides 2 sugar units Oligosaccharides 3- 10 units P ol y sac c h ar i d e s >10 e . g . G l uco s e, fructose etc e.g.Sucrose e.g. Maltotriose Homoglycans e.g. starch, glycogen Heteroglycans e.g. GAGs or glycosaminoglycans

7. Carbohydrates that cannot be hydrolysed into simpler carbohydrates are called as monosaccharides . Structure and Nomenclature The general formula C n H 2n O n W ith one of the carbons being the carbonyl group of either an aldehyde or a ketone. The most common monosaccharides have three to eight carbon atoms. The suffix-ose indicates that a molecule is a carbohydrate, and the prefixes tri , tetr- , pent- , and so forth indicate the number of carbon atoms in the chain like, triose , tetrose , pentose, etc. Monosaccharide containing an aldehyde group are classified as aldoses ; those containing a ketone group are classified as ketoses. 1. Sucrose (C 12 H 22 O 11 ) + H 2 O acid or certain enzyme Glucose (C 6 H 12 O 6 ) + Fructose (C 6 H 12 O 6 ) Monosaccharides Disaccharides

8. Monosaccharide further classified on the basis of functional group and number of carbon atoms present in their structure 3 Trioses Aldotriose e.g. glyceraldehyde Ketotriose e.g. Dihydroxyacetone 4 T e t r oses Aldotetrose e.g. Erythrose Ketotetrose e.g. Erythrulose 5 P en t o s e s Aldopentoses e.g Arabinose, Xylose, Ribose Ketopentoses e.g. Xylulose, Ribulose 6 H e x o se s Aldohexose e.g. Glucose, Galactose, Mannose Ketohexose e.g. Fructose 7 H e p t os e s Aldoheptose: Glucoheptose Ketoheptose e.g Sedoheptulose No. of carbon atom Generic name ALDOSE KETOSE On the basis of functional group On the basis of no. of carbon atom

9. Structural aspects of monosaccharides Stereoisomerism Compounds having same structural formula, but differing in spatial configuration as known as stereoisomers . Asymmetric carbon/ Chiral carbon: Four different groups are attached to the same carbon. The number of asymmetric carbon atoms (n) determines the possible isomers of a given compound which is equal to 2 n e.g. glucose contains 4 asymmetric carbons thus having 16 isomers. The reference molecule is glyceraldehyde . All monosaccharides can be considered as molecules derived from glyceraldehyde by successive addition of carbon atoms.

10. D- and L- isomers D and L Isomers are mirror images of each other. The spatial orientation of H & OH groups on the C- atom (C5 for glucose), adjacent to the terminal primary alcohol carbon determines whether the sugar is D or L Isomer. If the OH group is on the right side, the sugar is of D- Isomer. If the OH group is on the Left side, the sugar is of L- Isomer. Mammalian tissues have D- sugars. Penultimate carbon Penultimate carbon

11. Optical activity/ Optical Isomerism Optical activity is a characteristic feature of compounds with asymmetric carbon atom. Carbon atom can have four different groups then the carbon atom will possess asymmetry. A carbon atom is said to be asymmetric when its mirror images are non-super imposable on each other.

12. Theses types of compounds are called enantiomeric pair . Enantiomers Have identical physical properties but they interact differently with polarized light. When a beam of polarized light is passes through a solution of an optical isomer, it will be rotated either to the right or left. Depending on the rotation, molecules are called dextrorotatory (+) or levorotatory (-). The optical rotation is measured by an instrument called polarimeter . [α] λ T = α/ l x C [α] λ T = specific rotation at temp. T with wavelength λ α = observed rotation L = length of sample tube C= concentation in gm/ml

13. Racemic mixture : If D & L isomers are present in equal concentration, it is known as racemic mixture. NOTE: Racemic mixture does not exhibit any optical activity, since the dextro and levorotatory activities cancel each other. Specific rotation of some sugars

14. Epimers If two monosaccharides differ from each other in their configuration around a single specific carbon atom, they are referred as epimers to each other. Glucose & galactose are C4-epimers. Glucose & mannose are C2-epimers Inter-conversion of epimers is known as epimerization, epimerase catalyzes this reaction.

15. Anomerism – Mutarotation Anomers have same composition but differ in the orientation of groups around anomeric carbon atom. Anomeric carbon is a hemiacetal or carbonyl carbon atom, e.g. 1 st carbon atom in glucose is anomeric carbon atom. Carbonyl carbon atom becomes asymmetric because of ring structures of monosaccharides in solution thus anomers are encountered in cyclic structures of monosaccaharides . The alpha & beta cyclic forms of D-glucose are known as Anomers . They differ from each other in the configuration only around C1 known as anomeric carbon. In case of alpha anomer , the OH group held by anomeric carbon is on the opposite side of the group CH 2 OH of sugar ring

16. Anomers are expressed as α and β forms. In α form “OH” group is below the plane (OH group is oriented away from the oxygen atom) In β form “OH” group is above the plane (OH group is oriented towards the oxygen atom) Mutarotation : When D-glucose is crystallized at room temperature and a fresh solution is prepared, its specific rotation of polarized light is 112 o ; but after 12- 18 hrs it changes to +52.5 o Mutarotation is defined as the change in the specific optical rotation representing the interconversion of α and β forms of D-glucose to an equilibrium mixture.

17. Glucose and Fructose has two anomers α and β

18. Cyclization Less then 1% of CHO exist in an open chain form. Predominantly found in ring form . involving reaction of C-5 OH group with the C-1 aldehyde group or C-2 of keto group. Six membered ring structures are called Pyranoses . Five membered ring structures are called Furanoses . S traight chain form

19. PROPERTIES OF MONOSACCHARIDES Physical properties: Monosaccharides are colourless, crystalline compounds, readily soluble in water and sweet in taste. Their solutions are optically active and exhibit mutarotation . 2. Chemical properties: a) Reduction: 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. D-Glucose  D- Sorbitol D-Fructose  D- Sorbitol+ D - Mannitol

20. b) Oxidation: upon oxidation aldose sugars like glucose yields carboxylic acid, the aldehyde group is oxidized to carboxyl group to produce respective acids. Glucose  Gluconic acid Mannose  Mannonic acid Galactose  Galactonic acid

21. c) Formation of esters: Hydroxyl groups of sugars can be esterified to form acetates, propionates, benzoates, etc. Sugar phosphates are of great biological importance. Metabolism of sugars inside the body starts with phosphorylation . e.g Glucose 6-P0 4 d) Formation of osazone : this test is given by reducing sugar like, glucose, fructose, lactose and maltose. In this test phenyl hydrazine is reduced to phenyl hydrazone by sugar solution. Phenyl hydrazone when heated with more amount of phenyl hydrazine forms yellow crystals of osazone .

22. e) Furfural formation/Dehydration: Monosaccharides when treated with concentrated H 2 SO 4 undergoes dehydration with the removal of 3 molecules of water. Hexoses give hydroxymethyl furfural and pentoses give furfural. Furfurals condense with phenolic compounds to give various colors . E.g. Molisch’s test: General test for carbohydrates (H 2 SO 4 and α- naphthol ). Rapid Furfural and Seliwanoff’s test: Tests for presence of keto group

23. Some important Monosaccharides

24. 2. When two monosaccharides (similar or dissimilar) are combined together by glycosidic linkage, a disaccharide is formed. All are isomers with molecular formula C 12 H 22 O 11 On hydrolysis they yield 2 monosaccharide which soluble in water Even though they are soluble in water, they are too large to pass through the cell membrane. There are two types Non-reducing Sucrose T r eh a lo s e Cane sugar in yeast Reducing Lactose Mal t o s e Milk sugar Malt sugar

25. Condensation and Hydrolysis—Forming and Breaking Glycosidic Bonds The –OH group that is most reactive in a monosaccharide is the one on the anomeric carbon. When this hydroxyl group reacts with another hydroxyl group on another monosaccharide a glycosidic bond is formed. During this reaction, a molecule of water is eliminated as two molecules join.

26. Condensation reaction is a type of reaction that occurs when two molecules are joined and a water molecule is produced. This type of reaction is referred to as a dehydration reaction . Condensation reactions occur between different types of functional groups that contain an –H in a polar bond, like O–H or N–H, and an –OH group that can be removed to form water. Hydrolysis reaction is the reverse of a condensation reaction. A larger molecule forms two smaller molecules and water is consumed as a reactant.

27. In the case of maltose, the glycosidic bond is specified as α(1→4) and is simply stated as alpha-one-four. If the –OH group had been in the beta configuration when the glycosidic bond was formed, the bond would be in the β(1→4) configuration. The molecule formed would be named cellobiose and would have a different two-dimensional and three-dimensional shape than maltose. Maltose

28. Sucrose (glucose+ fructose) Sucrose is known as table sugar. It is the most abundant disaccharide found in nature. Sucrose is found in sugar cane and sugar beets. The glycosidic bond is α β ( 1→ 2). Both anomeric carbons of the monosaccharides in sucrose are bonded, therefore, sucrose is non-reducing sugar. It will not react with Benedict’s reagent. Also it not form osazone crystals in osazone test. When hydrolyzed, it forms a mixture of glucose and fructose Clinical Importance:- -dental caries -Bypasses metabolic check points- OBESITY - Sucrase deficiency

29. Inversion of Sucrose Hydrolysis of sucrose (optical rotation +66.5 o ) will produce one molecule of glucose (+52.5 o ) and one molecule of fructose (-92 o ) Therefore the products will change the dextrorotation to levorotation (INVERSION) Equimolecular mixture of glucose and fructose thus formed is called as Invert Sugar The enzyme producing hydrolysis of sucrose is called INVERTASE

30. Maltose (glucose+ glucose) Maltose is known as malt sugar. 2 glucose residues α ( 1 → 4) linkage Another form is α ( 1 → 6) called as Isomaltose . It is formed by the breakdown of starch. Malted barley, a key ingredient in beer, contains high levels of maltose. During germination of barley seeds, the starch goes through hydrolysis to form maltose. This process is halted by drying and roasting barley seeds prior to their germination. One of the anomeric carbons is free, so maltose is a reducing sugar. Osazone test:- Star shaped or flower petal shaped

31. Lactose ( galactose + glucose) Lactose is known as milk sugar. It is found in milk and milk products. The glycosidic bond is (1→4). An intolerance to lactose can occur in people who inherit or lose the ability to produce the enzyme lactase that hydrolyzes lactose into its monosaccharide units. One of the anomeric carbons is free, so lactose is a reducing sugar . Osazone test – Powder Puff or hedgehog shaped

32. Homogl y c an Or Homopolysaccharide Heteroglycan Or Heteropolysaccharide 3. Polysaccharides Polysaccharides are large molecules containing 10 or more monosaccharide units. Carbohydrate units are connected in one continuous chain or the chain can be branched. Storage polysaccharides contain only α - glucose units. Three important ones are starch, glycogen, and amylopectin . Structural polysaccharides contain only β - glucose units. Two important ones are cellulose and chitin. Chitin contains a modified β - glucose unit

33. Homopolysaccharides (all one type of monomer), e.g., glycogen, starch, cellulose, chitin, inulin , dextran . Heteropolysaccharides (different types of monomers), e.g., peptidoglycans , glycosaminoglycans Branched polysaccharides Unbranched / Linear polysaccharides

34. Starch Carbohydrates of the plant kingdom Sources: Potatoes, tapioca, cereals (rice, wheat) and other food grains Starch is a homopolymer composed of D-glucose units held by α - glycosidic bonds. Composed of two polysaccharide components- Amylose & Amylopectin Amylose : Amylose makes up 20% of plant starch and is made up of 250–4000 D glucose units bonded α (1→4) in a continuous chain. Long chains of amylose tend to coil. Mol wt =400,000 or more It is water soluble α - amylose HOMOPOLYSACCHARIDES

35. Amylopectin : Th e insol u b l e par t a b sorb s w a t er and f orm s p a s t e like gel; Amylopectin makes up 80% of plant starch and made up of glucose units, but is highly branched with molecular weight more than 1 million. The branching points are made by α- 1, 6 linkage

36. Hydrolysis of Starch About every 25 glucose units of amylopectin , a branch of glucose units are connected to the glucose by an α(1→6) glycosidic bond. During fruit ripening, starch undergoes hydrolysis of the α(1→4) bonds to produce glucose and maltose, which are sweet. When we consume starch, our digestive system ( α -amylase) breaks it down into glucose units for use by our bodies. Starch will form a blue coloured complex with iodine ; this color disappears on heating and reappears when cooled. This is a sensitive test for starch. When starch is hydrolyzed by mild acid, smaller and smaller fragments are produced. The hydrolysis for a short time produces amylodextrin (violet color with iodine and non-reducing). Further hydrolysis ……………. amylodex  erythrodex  archrodextrin  Maltose

37. 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. A homopolysaccharide (number of glucose units upto 25000): linear chain of α (1→4) linked glucosyl residues with branches joined by α (1→6) linkages More energy in a smaller space. 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.

38. Cellulose Glucose units combined by β -1,4 linkages. Straight line chain with no branches. This allows chains to align next to each other to form a strong rigid structure. Mol wt 2-5 million. Cellulose is an insoluble fiber in our diet because we lack the enzyme cellulase to hydrolyze the β -1,4 glycosidic bond . Whole grains are a good source of cellulose. Cellulose is important in our diet because it assists with digestive movement in the small and large intestine. Some animals and insects can digest cellulose because they contain bacteria that produce cellulase . Commercial applications: nitrocellulose, cellulose acetate membranes for electrophoresis .

39. Chitin Chitin makes up the exoskeleton of insects and crustaceans and cell walls of some fungi. It is made up of N -acetyl glucosamine containing β (1→4) glycosidic bonds. It is structurally strong. Chitin is used as surgical thread that biodegrades as a wound heals. It serves as a protective Exoskeleton in crustacea and insects . Chitin is also used to waterproof paper, and in cosmetics and lotions to retain moisture .

40. Dextrins / Dextrans Highly branched homoglycan containing Glucose residues in 1-6, 1-4 and 1-3 linkages. Produced by microbes. Mol. wt:- 1-4 million. As large sized, they will not move out of vascular compartment so used as plasma expanders. Inulin D -fructose in β-1,2 linkages. Source: Bulbs and tubers chicory, dahlia, dandelion, onions, garlic. Not metabolized . Not absorbed nor secreted by kidneys so, used to measure GFR.

41. HETEROPOLYSACCHARIDES Polymers made from more than one kind of monosaccharides or monosaccharide derivatives. e.g., mucopolysaccharides , Agar & Agarose and glycoproteins . MUCOPOLYSACCHARIDES First isolated from mucin so called mucopolysaccharides Long, Unbranched heteropolysaccharide , made of repeating disaccharide units containing uronic acid & amino sugars. These are more commonly known as Glycosaminoglycans (GAG). Amino sugar – Glucosamine or Galactosamine (Present in there acetylated form) Uronic acid – D- Glucuronic acid Major components of extracellular matrix of connective tissue, including bone and cartilage, synovial fluid, vitreous humor and secretions of mucus producing cells.

42. Hyaluronic acid It is the simplest mucopolysaccharide and is a linear polymer of disaccharides which form the repeating unit. Each disaccharide is linked to the next by β - 1,4 glycosidic bonds. It consists of two alternative units of D- glucuronic acid and N-acetyl D-glucosamine, linked by β -1,3 to give a thread like structure . Present in Synovial fluid of joints, vitreous humor , connective tissues and cartilage. Sulfate free Sulfate containing Hyaluronic acid Chondroitin Sulphate, Dermatan sulphate, keratan sulphate, Heparin, Hepa r an Sulp h a t e

43. Functions: Serves as a lubricant and shock absorbant in joints. Acts as seives in extracellular matrix. Permits cell migration during morphogenesis & wound repair. Hyaluronidase is an enzyme that breaks β1 – 4 linkages of hyaluronic acid. Present in high concentration in seminal fluid, & in certain snake and insect venoms. Hyaluronidase enzyme of semen degrades the gel around ovum & allows effective penetration of sperm into ovum, thus helps in fertilization. Condroitin sulphates Widely distributed in bone, cartilage, skin, heart & tendons. The repeating unit is a disaccharide and consisting of alternate units of D- glucuronic acid linked to sulphate ester of N- acetyl galactosamine . Functions: In cartilage, it binds collagen & hold fibers in a tight strong network. Role in Compressibility of cartilages in weight bearing.

44. Heparin Heparin is a medically important polysaccharide because it prevents clotting in the bloodstream. It is a highly ionic polysaccharide of repeating disaccharide units of an oxidized monosaccharide and D-glucosamine. Heparin also contains sulfate groups that are negatively charged. present intracellular: In granules of mast cells and also in lung, liver and skin . Functions: It is an anticoagulant (prevents blood clotting) Heparin helps in the release of the enzyme lipoprotein lipase (LPL) which helps to clear the lipidemia after fatty meal – so called clearing factor.

45. AGAR Contains galactose , glucose & other sugars. Obtained from sea weeds Functions: Cannot be digested by bacteria. So used as supporting agent to culture bacterial colonies. Also as support medium of immuno diffusion & immuno -electrophoresis. AGAROSE Galactose and 3,6 anhydrous galactose units. Used as matrix for electrophoresis. GLYCOPROTEINS Several proteins are covalently bound to carbohydrates which are referred to as glycoproteins . The carbohydrate content of glycoproteins varies from 1% to 90% by weight. The term mucoprotein is used for glycoproteins with carbohydrate concentration more than 4%. Glycoproteins are very widely distributed in the cells and perform variety of functions like enzymes, hormones, transport proteins, structural proteins, blood group antigens and receptors. The carbohydrates found in glycoproteins include mannose, galactose , N-acetyl glucosamine, N-acetyl galactosamine , xylose and N- acetylneuraminic acid (NANA)

46. Qualitative tests for Carbohydrates To study the properties of carbohydrates To identity of an unknown carbohydrate by carrying out a series of chemical reactions 1 . SOLUBILITY (to differentiate mono and disaccharides from polysaccharides ) Mono and disaccharides are soluble in water to give clear solution. Whereas, polysaccharides are insoluble in water. 2 . MOLISCH TEST (for all carbohydrates) Principle: Carbohydrates when treated with concentrated sulphuric acid undergo dehydration to give furfural derivatives. These compounds condense with Alpha naphthol to form colored products. Pentoses yield furfural while Hexoses yield 5-Hydroxy methyl furfurals.

47. This is a sensitive but a non- specific test and is given positive by all types of carbohydrates. If the oligosaccharides or polysaccharides are present they are first hydrolysed to monosaccharides which are then dehydrated to give the test positive. 3. BENEDICT’S TEST ( to differentiate reducing sugars from non-reducing sugars) -Carbohydrates with free aldehyde or ketone groups have the ability to reduce solutions of various metallic ions. -Reducing sugars under alkaline conditions tautomerise and form enediols . - Enediols are powerful reducing agents. -They reduce cupric ions to cuprous form and are themselves converted to sugar acids. -The cuprous ions combine with OH- ions to form yellow cuprous hydroxide which upon heating is converted to red cuprous oxide.

48. 4. FEHLING’S and TOMMER’S TEST ( to differentiate reducing sugars from non-reducing sugars ) Reducing sugar reduces copper ions present in the Fehling solution so as to give red precipitate 5. BARFOED’S TEST (to differentiate monosaccharides from disaccharides ) Aldoses and ketoses can reduce cupric ions even in acidic conditions. This test is used to distinguish reducing mono saccharides from disaccharides by controlling pH and time of heating. Mono saccharides react very fast whereas disaccharides react very slowly. The positive reaction indicates the presence of a reducing mono saccharide . On prolonged heating disaccharides can also give this test positive. Hence, the solution should be boiled for 3 minutes only.

49. 6. SELIWANOFF’S and RAPID FURFURAL TEST (to differentiate ketoses from aldoses ) Keto hexoses on treatment with hydrochloric acid form 5-hydroxy methyl furfural which on condensation with resorcinol gives a cherry red colored complex. 7. HYDROLYSIS OR INVERSION TEST (to confirm sucrose ) Sucrose is a non-reducing sugar, since it does not have free aldehyde or ketone group to cause reduction, hence it gives a negative reaction with Benedict’s reagent. But upon boiling with HCl , sucrose is hydrolyzed to yield glucose and fructose, which give positive reactions with benedict and Seliwanoff reagents.

50. 8. OSAZONE TEST (to differentiate among reducing sugars by their crystalline structure ) A solution of reducing sugar when heated with phenyl hydrazine, Characteristic yellow crystalline compounds called Osazone are formed. These crystals have definite crystalline structure, precipitation time and melting point for different reducing sugars. Needle shaped glucosazone crystals as viewed under the microscope Galactosazone crystals as viewed under the microscope(Rhombic plates) Sun flower shaped Maltosazone Powder puff/hedge hog shaped Lactosazone

51. 9. IODINE TEST (for all polysaccharides) Iodine forms a coordinate complex between the helically coiled polysaccharide chain and iodine centrally located within the helix due to adsorption. The color obtained depends upon the length of the unbranched or linear chain available for complex formation Left to right : Lugol's iodine, starch solution, starch solution with iodine.

52. Diseases related to Carbohydrates metabolism Diabetes mellitus (D.M.) When the body is unable to utilize the glucose then there is an appearance of excessive sugar in the blood, as well as in the urine called glycosuria and the disease is termed as diabetes mellitus. It is a group of metabolic disorders with a common characteristic feature of hyperglycemia . The blood sugar level is regulated by the pancreatic protein hormone insulin, which is secreted by the β - cells of islets of langerhans of pancreas. Hyperglycemia in D.M. Is due to defect in insulin action, secretion or both. Diabetes mellitus is broadly classified into 2 categories: Type 1 diabetes : it is characterised by absolute deficiency of insulin due to destruction of β - cells of pancreas. Type 2 diabetes: it is caused due to peripheral resistance to insulin action and inadequate secretion of insulin by β - cells of pancreas.

53. The blood glucose level rises remarkably (>200 mg/dl) than normal (70-120 mg/dl) in D.M. Characteristics or Symptoms: hyperglycemia (increased in blood sugar), glycosuria (sugar in urine), increased fat and protein metabolism, ketosis (increased in ketone bodies in tissue), hypercholesterolemia (blood LDL increased), atherosclerosis (plaque formation on the wall of artery), polyuria (increased urine volume), polydipsia (increased thirst), polyphagia (excessive ingestion of food), coma and death. Treatment: D.M., can be treated by administering insulin subcutaneously or by giving oral antidiabetic / oral hypoglycemic agents. Patient may advised to take protein diet but not the carbohydrate diet.

54. 2) Glycosuria Appearance of usually high amounts of sugar in the urine is called as glycosuria . Depending upon the causes, glycosuria has been classified into various groups as: Alimentary glycosuria : this term is used to denote glysouria which sets up after the consumtion of excessive amounts of sweet things like glucose, cane sugar, sweets or even starch via diet. Diabetic glycosuria : it is pathological condition in which carbohydrate metabolism gets impaired which results into appearance of sugar in the urine. Renal glycosuria (Renal diabetes): this occurs due to some defect in the renal tubular transport mechanism of glucose. Adrenaline glycosuria : it is also known as emotional or psychic glycosuria . It occurs generally due to hypersecretion of adrenaline hormone from adrenal cortex. Glycosuria can be detected in urine by benedicts or barfoed’s tests.

55. 3) Galactosemia Due to deficiency of the enzyme galactose 1- phosphate uridyl transferase and galactokinase , galactose can not be converted into glucose, which leads to a condition called as galactosemia . It is characterized by increased galactose levels in blood and urine. Accumulated galactose is converted into galactitol , which is responsible for development of cataract. The clinical symptoms of galactosemia are jaundice, hepatospleenomegaly , mental retardation, etc. 4) Fructose intolerance One of the very normal hexose sugar of fruits (i.e. Fructose) gets normally metabolised to give energy and CO2, but defective metabolism of fructose develop in high concentration of this sugar in blood, disorder known as fructose intolerance.

56. 5) Glycogen storage diseases: The metabolic abnormalities related with glycogen synthesis and degradation are collectively termed as glycogen storage diseases. These are: Van glerke’s disease: it is due to hepatic glycogen storage. Pompe’s disease: it is due to storage of normal glycogen in almost every organ of the body, including the heart. Limit dextinosis ; forbe’s or cori’s disease: it is due to increased deposition of glycogen with very outer branches in the liver and other tissues. Amylopectonosis or anderson’s disease: it is due to deficiency of branching enzymes which results in accumulation of glycogen.

57. Functions/ Role of Carbohydrates Serve as m ain sources of ENERGY in body ( 4kcal/g ) As structural component: Carbohydrates are the essential components of some structural materials of living organisms: Monosaccharides act as a constituents of nucleic acids, coenzymes, flavoproteins and blood group substances. Immuno -polysaccharides play an important role in the resistance of infections. Hyaluronic acid is a viscous substance in the matrix of connective tissue and various other tissues, acts as a good lubricant. Heparin, is a naturally occuring anticoagulant, prevents blood coagulation. glucoronic acid, acts as detoxifying agent by forming complex with toxic substances. Glycosides are the components of steroid hormones, act as cardiotonic agent.

58. 2) Supply and storage of energy: carbohydrates, supplies and stores energy. About 60% of energy is supplied by the catabolism of carbohydrates. 1 gm of carbohydrates on oxidation gives 4 calories of energy. Glucose is the sole form of energy for the brain and nervous tissues. stored glycogen, in the liver, also provides energy in absence of glucose. 3) Regulates fat metabolism: carbohydrates are required for the normal oxidation of fats. In the absence of carbohydrates, fat deposition occurs in the body and may give risk to ketosis. 4) Carbohydrates provides essential energy to the body by sparing protein for building of tissues. 5) It also plays a role in gastrointestinal functions. Polysaccharides like cellulose, pectin give bulk and help in the peristaltic movements of the digestive tract.

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