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CHEMISTRY OF CARBOHYDRATES

CHEMISTRY OF CARBOHYDRATES. Dr. Vinitha Ramanath Pai Professor Dept. of Biochemistry, YMC. INTRODUCTION CONTENTS DEFINITION BIOMEDICAL IMPORTANCE CLASSIFICATION WITH EXAMPLES STRUCTURE, CHEMICAL PROPERTIES, FUNCTIONS OF INDIVIDUAL CLASSES OF CARBOHYDRATES

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CHEMISTRY OF CARBOHYDRATES

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  1. CHEMISTRY OF CARBOHYDRATES Dr. VinithaRamanathPai Professor Dept. of Biochemistry, YMC

  2. INTRODUCTION CONTENTS DEFINITION BIOMEDICAL IMPORTANCE CLASSIFICATION WITH EXAMPLES STRUCTURE, CHEMICAL PROPERTIES, FUNCTIONS OF INDIVIDUAL CLASSES OF CARBOHYDRATES Revision exercises on slides : 33 – 37; 90 – 94; 116 - 121 Answers on Slides : 38 ; 95 ; 122 respectively Question bank : slides 134 and 135

  3. Introduction Carbohydrates are…….. • Widely distributed in plant and animal kingdoms • One of the most abundant class of bio - molecules in nature • Functions :structural role and metabolic role.

  4. Introduction What are carbohydrates ? Organic compounds i.e., compounds of carbon Formula : Cn(H2O)n Hydrates of carbon

  5. What are the atoms present in carbohydrates Atoms : Main C, H and O. Some also contain N, P or S. Fructose Glucose

  6. What are the functional groups in carbohydrates ? Aldehyde Keto Hydroxyl groups - more than one Polyhydroxy And also contain either an Aldehyde or a Keto group Fructose Glucose

  7. Definition Carbohydrates are…….. • Polyhydroxyaldehydes or Polyhydroxyketones, or compounds which give them on hydrolysis. • Polyhydroxy alcohols with free or potentially free aldehyde / keto groups or compounds which yield these on hydrolysis.

  8. Biological Importance Carbohydrates have structural and metabolic functions Metabolic functions • Carbohydrates and energy : • Main source of metabolic energy in the body, e.g., Glucose • Storage forms of energy, e.gs., Starch in plants Glycogen in animals • Ribose is a component of ATP (energy coin of the cell)

  9. Biological Importance……Metabolic functions………. • Dietary fibre, e.gs., cellulose, hemicellulose, and pectins • Detoxification of drugs and bilirubin, e.g., Glucuronic acid • Synthesis of other compounds, i.e., lipids and amino acids - from the carbon skeletons of carbohydrates.

  10. Biological Importance……. Carbohydrates have the following structural functions • Components of structural biomolecules and cell membranes : • e.gs. : In nucleic acids: Ribose in RNA and Deoxyribose in DNA • Nucleotides, e.g., ATP , cAMP contain Ribose • Mucopolysaccharides of ground substances of tissues, synovial fluid of joints etc. • Glycoproteins of blood group antigens, • Glycoproteins and glycolipidsof cell membranes • Cellulose of plants, Chitin of insects, etc.

  11. Medical Importance: • Some important disorders associated with carbohydrates are- • Diabetes mellitus, • Lactose intolerance, • Galactosemia, • Glycogen storage diseases and, • Mucopolysaccharidoses.

  12. Medical Importance…… • Carbohydrate containing drugs (glycosides) are important in Therapeutics. e.g., 1. cardiac glycosides. • Function : Agents whichincrease contractility of heart muscle.

  13. Medical Importance…… • Antibiotics, e.g., Streptomycin, • Use : treatment of tuberculosis • Ouabain • Use : Inhibits Na+ - K+ Pump

  14. Classification of Carbohydrates • 3 classes • Basis : No. of monosaccharide units present / got on hydrolysis Carbohydrates 3 classes • MonosaccharidesOligosaccharidesPolysaccharides • Made up of more than 10 monosaccharide units • Single unit, i.e., • single chain of Carbon atoms • Made up of 2 – 10 monosaccharide units

  15. Classification of Monosaccharides with examples 2 sub classifications E.g : Glucose Eg : Fructose

  16. Classification of Monosaccharides with examples 2nd sub classification Aldoses Ketoses e.g., Glyceraldehyde, Dihydroxy acetone e.g., Erythrose, Erythrulose e.g., Ribose, Ribulose e.g., Glucose, Fructose e.g., - SedoHeptulose

  17. Classification of Oligosaccharides with examples Carbohydrates Oligosaccharides (2-10 monosaccharides) Disaccharides Trisaccharides Others 2 monosaccharides 3 monosaccharides Examples : Maltotriose Raffinose Examples : Maltose Lactose Sucrose

  18. Sub -classification of oligosaccharides Disaccharides - made up of 2 monosaccharides Trisaccharides - made up of 3 monosaccharides Tetrasaccharides - 4 monosacccharides • Pentasaccharides - 5 monosacccharides • Hexasaccharides - 6monosacccharides Others

  19. Glycosidic bonds • Glycosidic bonds : Is the bond which links monosaccharides in oligosaccharides and polysaccharides. Formation : formed by dehydration between two hydroxyl groups on two monosaccharides.

  20. Sub -classification of dissacharides with examples Definition of Dissacharides Two monosaccharides linked by one glycosidic bond • 2 sub - classes • Basis : Reducing property Disaccharides 2 sub classes • Reducing disaccharidesNon reducing disaccharides • Reduce cupric ions to cuprous ions • Do not reduce Cu++ to Cu+ • Eg : Maltose; Lactose • Eg : Sucrose; Trehalose

  21. Sub -classification of polysaccharides with examples Definition of Polyssacharides More than ten monosaccharides linked by glycosidic bonds • 2 sub - classes • Basis : On the type of monosaccharides got on hydrolysis Polysaccharides 2 sub classes • HomopolysaccharidesHeterpolysaccharides • Same type of monosaccharide units • Different types of monosaccharide units • Eg : Hyaluronic acid, • Chondroitin sulfate • Eg : Starch, glycogen

  22. Monosaccharides • Monosaccharidesare the ……. • Simplest carbohydrates • Have single chain of carbon atoms (3- 7 carbons) • The basic units of all carbohydrates • Hydrolysis products of oligosaccharides and polysaccharides. • Empirical formula is Cn(H20)n. (n = no. of carbon atoms) • Mono-and disaccharides are referred to as ‘sugars’ - they are sweet to taste (Greek: saccharon means sugar).

  23. Monosaccharides Monosaccharides have single chain of carbons Fructose Glucose

  24. Numbering carbon atoms in Monosaccharides starts from the carbonyl (C=O) end. The carbonyl carbon atom in Aldoses is C1 Ketoses is C2. 1 1 2 2 3 3 4 4 5 5 6 6 Fructose Glucose

  25. Ring structure of Monosaccharides • In aqueous solution, monosaccharides containing 5 or more carbon atoms exist mostly as ring structures – • either 5 membered ring - furanose ring • or 6 membered ring - pyranose ring

  26. Straight chain structure Structure of Monosaccharides 6 membered ring - pyranose ring e.g., Glucose; Galactose; Mannose Glucose

  27. Straight chain structure Structure of Monosaccharides 5 membered ring - furanose ring e.g., Fructose; Ribose; Deoxyribose Fructose

  28. Sub-classification of Monosaccharides • Sub classifications : 2 types • Based on functional group present. • Based on no. of carbon atoms present

  29. Combining the two classifications , monosaccharides are named as follows :

  30. Examples for the monosaccharides

  31. Naming of Keto sugars • The names end in ‘ulose’ • Examples : • Erythrulose • Ribulose • Xylulose • Sedoheptulose

  32. Quiz ahead …………….. • 5 multiple choice questions……. • (Answers on slide 38)

  33. Quiz Question 1 : Find the odd one in this group Dihydroxy acetone Ribulose Mannose Fructose • c) Mannose • It is an Aldose

  34. Quiz Question 2 : Which of these has a aldehyde functional group and five carbon atoms Glucose Ribulose Erythrulose Xylose • d) Xylose • It is an Aldopentose

  35. Quiz Question 3 : An example for a carbohydrate with no nutritional value is Starch Pectin Glycogen Glucose • b) Pectin • It is a dietary fibre

  36. Quiz Question 4 : Ribose and Xylulose are Pentoses Hexoses Aldoses Ketoses • a) Pentoses • They are aldopentose and ketopentose, respectively 36

  37. Quiz Question 5 : Which of these is a structural homopolysaccharide Starch Chitin c) Glycogen d) Hyaluronic acid • b) Chitin • Made up of N-Acetylglucosamine

  38. Answers to the quiz from slides 26 - 31 Slide 27 MCQ 1 : c) Mannose (aldose ) Slide 28 MCQ 2 : d) Xylose (aldopentose) Slide 29 MCQ 3 : b) Pectin - Dietary fibre Slide 30 MCQ 4 : a) Pentoses Slide 31 MCQ 5 : b) Chitin

  39. Intermediates of Glycolysis Important monosaccharides Ribose is found in RNA and Deoxy ribose is found in DNA; Nucleotides, cAMP Intermediates of HMP Shunt pathway Principal blood sugar and main source of energy (Dextrose) Main sugar in Honey Fruit sugar, (Levulose)

  40. Monosaccharides of Physiologic Importance Pentoses: D-Arabinoseand D-Xyloseare constituents of glycoproteins Hexoses:

  41. Isomerism in Monosaccharides Monosaccharides exhibit basically 2 types of isomerism – Aldose - ketose isomerism Stereoisomerism

  42. AldoseKetose Isomerism • Both have 6 ‘C’ atoms • Both have same molecular formula C6H12O6 • Different structural formula • Different Functional groups Glucose Fructose

  43. 1. Aldose-ketose isomerism Monosaccharides having Same number of carbon atoms and molecular formula but different structural formula, i.e., due to different functional groups (aldehyde or keto) are referred to as aldose-ketose isomers.

  44. Examples for Aldose-ketose isomerism

  45. Stereoisomers have • same empirical formula and structural formulae but • differ in their configuration (arrangement of atoms/groups in space). • Compounds having asymmetric carbon atoms exhibit stereoisomerism. 2. Stereoisomerism Which compounds show stereoisomerism ?

  46. 2. Stereoisomerism Asymmetric carbon atom A carbon atom whose 4 valencies have 4 different groups • For a compound having ‘n’ number of asymmetric atoms 2n number of isomers is possible. • All monosaccharides / sugars except dihydroxyacetone contain asymmetric carbon atoms.

  47. 2. Stereoisomerism Orientation of -H and -OH groups In straight chain structure : Right or left In ring structure Above the plane of the ring or below the plane of the ring Glucose

  48. 2. Stereoisomerism • There are 2 possible orientations of –H and –OH groups around asymmetric carbon atoms of sugars. • In the conventional open chain structural representation, –H or –OH groups fall either to the left or to the right. • In the ring structure, –H or –OH groups will be either above the plane of the ring or below the plane of the ring

  49. Types of Stereoisomerism Stereoisomerisms are of 3 types Basis : based on the configuration around an (any one) asymmetric carbon atom D-L Stereoisomerism Epimerism Anomerism

  50. 2. Stereoisomerism DL Isomerism 5 5 • Penultimate carbon (last but one carbon) 6 6 Last carbon - Ultimate carbon D-Glucose Glucose L-Glucose Glucose

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