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Medical Biochemistry and Molecular Biology CARBOHYDRATE CHEMISTRY 2 By Ayman Elsamanoudy Objectives (ILOs) I. to study the definition, classification of carbohydrates II. to know the biological importances of carbohydrates. III. to know the important body structure formed by carbohydrate molecules and study its functions . IV. to understand how any disorder in carbohydrates structure or function leads to disease. 3 Carbohydrates are : Organic compounds composed of C.H.O. Contain more than hydroxyl group. Contain active carbonyl group ;aldehyde at C1 or ketone group at C2. Generally but not always the hydrogen and oxygen in carbohydrates are present in the proportion of 2H and one oxygen atoms as in water. 4 Definition: Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones and compound giving them on hydrolysis 5 Function of carbohydrates 1. They serve as energy stores and fuels. 2. They enter in the structure of cell membranes. 3. Pentose sugars (ribose and deoxyribose) enter in the structure of nucleic acids. 4. Carbohydrates enter in the structure of glycoproteins and glycolipids. 5. Carbohydrates play important roles in recognition between cell types or recognition of cellular structures by other molecules. NB: Recognition events are important in normal cell growth, fertilization and transformation of cells. 6 Classification Monosaccharides Disaccharides Diff The simplest 2 carbohydrates. They contain only one sugar unit . -cannot hydrolysed Oligosaccharides Polyosaccharides monsacch. 3-10 monsacch. Units linked to More than Units linked to each other by glycosidic bond monsacch. each linked to each other other by Glucose …. by glycosidic bond Sucrose Starch ……. be into Lactose…… & 1-Maltotriose = 3 glucose units 2-Raffinose (tri-saccharide= glucose+glactose+fructose) 7 Units glycosidic bond simpler units Ex. 10 Monosaccharides Are carbohydrates which, contain only one sugar unit and cannot be hydrolyzed into smaller units ( the simplest form of carbohydrates). They are further classified according to: 1. Number of carbon atoms contain. 2. Whether they are aldehydes or ketones. 3. According to number of carbon atom as well as adlehydes and ketones. 8 9 Number of Carbons (Generic monosaccharide name) Aldose Functional Group Ketone Functional Group 3 (Triose) Aldotriose Ketotriose Triulose Aldotetrose Ketotetrose Tetrulose Aldopentose Ketopentose Pentulose Aldohexose Ketohexose Hexulose 4 (Tetrose) 5 (Pentose) 6 (Hexose) 10 Aldoses Ketoses 12 Structural formula of monosaccharides A) Straight (open) chain formula : B) Cyclic structural formula . 1-Fischer projection form: 2-Haworth form 1-simple chain formula (Acyclic form) 2- Cyclic structure formula: In the solution, the sugar which has an aldehyde group undergoes the following:Hydration of aldehyd group to form aldenol group>>>>>then condensation between OH group of aldenol and OH of C4 or C5 to form ring structure . a-Fischer projection formula:the b- Haworth formula: aldhyde or ketone group react Which may be : pyranose or with one OH group to form furanose hemiacetal or hemiketal Steps of the cyclic form construction: 1. Hydration of aldehyde or keto group to form aldenol or ketonol group producing aldenol or ketonol form of monosacharide. Furan ring H HO H CHO H C OH HO C H H C OH H C OH HO + CH2OH D-Glucose H2O H H OH C H C OH HO C H H C OH H C OH (or) HO CH2OH D-Glucose aldenol, unstable H HO H O H (or) Furan ring CH2OH HO C OH HO C H HO C H H C OH H C OH H C OH H C OH + CH2OH D-Fructose H2O HO C HO C H C H C CH CH2OH C=O CH (or) -D-F OR CH HO CH2OH D-Fructose ketonol, unstable O + C HO C H C H C H2C (or) -DPyran ring Then 2- The OH group from the aldenol group condenses with the OH : on C4 or C5 of the aldo-sugar to forms a ring or hemi-acetal structure with the liberation of H2O again. Keto-sugar condenses only with C5 or with C6 giving Hemiketal form . 17 The aldehyde or ketone group can react with a hydroxyl group to form a covalent bond. An aldehyde reacts with a hydroxyl group creates a hemiacetal. A ketone reacts with a hydroxyl group to form a hemiketal. 19 Haworth's formula: Because Fisher’s formula could not explain some of the chemical and physical characteristics of sugars, Haworth put forth his formula. . C and O atoms of the ring are drawn in the plane of the page. H and OH or other side groups are written on perpendicular plane. All groups located on the left side of fisher’s are written upwards. All groups located on the right side of fisher’s are written downwards Except in Last C in the ring . 5 membered oxy ring 22 6 membered oxy ring 23 24 MCQs The aldose sugar is (A) Glyceraldhyde (B) Ribulose (C) Erythrulose (D) Dihydoxyacetone 25 A triose sugar is (A) Glycerose (B) Ribose (C) Erythrose (D) Fructose A pentose sugar is (A) Dihydroxyacetone (B) Ribulose (C) Erythrose (D) Glucose 26 . Ribulose is a these (A) Ketotetrose (B) Aldotetrose (C) Ketopentose (D) Aldopentose A carbohydrate, commonly known as dextrose is (A) Dextrin (B) D-Fructose (C) D-Glucose (D) Glycogen 27 Which of the following is a keto sugar A) Galactose B) Fructose C) Glucose D) Mannose 28 Glycosidic bond is absent in A) Disacharide B) oligosacharide C) Monosacharide D) Polysacharide 29 Hydration of glucose leads to formation of A) Stable alcohol B) Unstable aldenol form of glucose C) Direct cyclization of glucose D) No effect 30 Fructofuranose is A) Straight chain formula of fructose B) Fischer projection formula of fructose C) Ketenol form of fructose D) 6 membered oxy ring of fructose 31 The predominant form of glucose in solution is (A) Acyclic form (B) Hydrated acyclic form (C) Glucofuranose (D) Glucopyranose 32 Asymmetric carbon atom (chiral carbon) Def: It is a carbon atom which is attached to 4 different group or atoms e.g. middle carbon of glyceraldhyde. Any substance having asymmetric carbon atom posses the following: I. Show optical activity. II. Show optical isomerism (stereoisomerism) 33 34 Optical activity DIFF:It is the ability of the compound to rotate plane polarized light either towards the right or towards the left. Plane polarized light: is an ordinary light after passing through special type of prism called Nicols prism (CaCO3), the light emerging form such prism vibrate in a single plain. 35 Types of optically active sugar solutions A. If the compound rotate plane polarized light to the right, it is called >>>>dextrorotatory, d or (+). Example: Glucose is dextrorotatory so it is sometimes called dextrose. B. If the compound rotate plane polarized light to the left, it is called>>>>>. levorotatory, l or (-). Example: Fructose is levorotatory so it is sometimes called levulose. NB :All monosaccharides are optically active, except dihydroxy acetone, this is due to the presence of asymmetric carbon atoms. 36 Measurement of optical activity By : Polrimeter or Polriscope Composition : 1- source of light (Na light). 2-A Nicol prism(polarizer):it converts ordinary scattered light into PPL. 3- A glass tube in which the exmined solution will be done. 4- Analyzer which determine the angel of rotation. 5- Detector 37 38 39 Specific rotation It is the angle of rotation specific for each optically active substance when the concentration of substance is 100 g/dl and the length of measuring tube is 10 cm using Na light at 20 Ċ. Examples : The specific rotation : 1. for glucose is + 52.5 & 2. for fructose is - 91. 40 Factors affecting specific rotation 1. 2. 3. 4. Type of light. Length of the tube. Nature and concentration of substance. Temperature. 41 Optical isomerism Def :Compounds having the same structural formulae (same chemical group) but differ in the way these groups are attached in space around only one of its asymmetric carbon atom. The number of optical isomers = 2n where n = number of asymmetric carbon atoms in a molecule. 42 Types of isomerism of monosacharides: 1-Enantiomers: (D & L configuration). 2-Anomers or α and β isomer. 3-Epimers. 4-Aldose and ketose isomers . 5-Pyranose and furanose isomers 43 Enantiomers: (D & L) isomers Concept: Two isomers which are mirror images . Reffered to : prelast carbon which is the last asymetric C atom . Types of enantiomers : 1- D form: OH attached to the right of prelast C. 2-L form: OH attached to the left of prelast C Description :They differ in all carbons (mirror image) but D & L configuration is according to H – OH orientation in the pre-last C. NB: The great majority of the sugars in humans are Dsugars 44 45 46 47 48 Anomers :α and β isomer Concept:These are isomers that differ in position of OH group at the anomeric carbon atom. Reffered to: anomeric C atom Def of annomeric C atom: is the asymmetric carbon atom obtained from active sugar group in the cyclic structure . Position of anomeric C:C1 in aldose and C2 of ketose). Types of anomers : 1- α sugar : OH group attached to the anomeric carbon is on the right side. 2- β sugar. OH group attached to the anomeric carbon is on the left side. 49 50 51 52 Epimers Concept :If two monosaccharides differ in configuration around only one asymtetric carbon atom other than anomeric C& the prelist C atom ,((the epimeric carbon))>>>> they are defined as epimers of each other. Referred to: epimeric carbon . Def of epimeric carbon : asymtetric carbon atom other than anoneric& the prelist C atoms. Examples : usually erpimers are described in pairs : . Glucose & galactose are C4 epimer. . 53 Glucose & mannose are C2 epimer 54 55 Aldose and ketose isomers Concept :Two isomers have the same molecular formula but differ in aldhyde group or ketone group Example :. glucose --- fructose ribose --- ribulose. 56 57 Pyranose and furanose isomers Glucose can be present in glucopyranose and as glucofuranose both are isomers. 58 59 60 MCQs The number of isomers of glucose is (A) 2 (B) 4 (C) 8 (D) 16 61 Isomers differing as a result of variations in configuration of the —OH and —H on carbon atoms 2, 3 or 4 of glucose are known as (A) Epimers (B) Anomers (C) Optical isomers (D) Steroisomers 62 The most important epimer of glucose is (A) Galactose (B) Fructose (C) Arabinose (D) Xylose 63 -D-glucose and -D-glucose are (A) Stereoisomers (B) Epimers (C) Anomers (D) Keto-aldo pairs 64 Which of the following is an epimeric pair? (A) Glucose and fructose (B) Glucose and galactose (C) Galactose and mannose (D) Lactose and maltose D-Glucose and D-glucose are related by (A) Epimers (B) Anomers (C) aldose ketose isomers (D) pyranose-furanose isomers 65 Sugar Derivatives They include: I. Sugar Acids. II. Sugar Alcohols. III. Deoxysugars. IV. Amino Sugars. V. Amino sugar acids. 66 Sugar Acid. Def: They are the oxidation products of monosaccharides Aldonic acids: deff Aldaric acids: Oxidation of carbonyl Oxidation of the last They group Oxidation Uronic acids: to group yields aldonic acids both carbonyl carbon and acid. last hydroxyl carbon, Glucuronic acid L iduronic acid 67 dicarboxylic carboxylic carbon yields uronic resulting from oxidation of of Gluconic acid glucose gives are Glucaric acid 1.Aldonic CHO H C HO C OH H COOH H C OH bromine water, O2 HO C H H C OH H C OH H C OH H C OH CH2OH D-Glucose CH2OH D-Gluconic acid 2-Uronic CHO H C HO C CHO OH H H C OH H C OH CH2OH D-Glucose H C H2O2 Dil. Nitric acid HO C OH H H C OH H C OH COOH D-Glucuronic acid 3-Aldaric CHO H C HO C COOH OH H H C OH H C OH CH2OH D-Glucose H C O2 Conc. Nitric acid HO C OH H H C OH H C OH COOH D-Glucaric acid CHO COOH H C OH HO C H OH H C OH OH H C OH H C OH HO C H H C H C CH2OH D-gluconic acid 71 COOH D-glucuronic acid Imortance of Iduronic acid : glycosaminoglycans formation (mucopolysaccharides) Imortance of Glucuronic acid : 1. Detoxication reactions. 2. Formation of glycosaminoglycans (mucopolysaccharides). 3. Metabolism of bilirubin. 4. Excretion of steroids. 72 73 L-ascorbic acid (vitamin C) It is a 6-carbon sugar acid. It is water soluble and optically active. Humans are unable to synthesize it and hence must be supplied in the diet. It has 2 forms: reduced form ( ascorbic acid ) oxidized form ( dehydroascorbic acid ) 74 Ascorbic acid (reduced form) 75 dehydrAscorbic acid (oxidized form) 2-Sugar alcohols (Alditols) Diff: It is the product of reduction of the active carbonyl group . Concept: Aldoses and Ketoses may be reduced at the carbonyl carbon to the corresponding polyhydroxy alcohols (sugar alcohols). Examples : D-glucose D-mannose D-fructose D-galactose D-ribose 76 D-sorbitol. D-mannitol. D-sorbitol and D-mannitol. D-galacticol. D-ribitol CHO CH2OH H C OH H C OH H C OH H2 H C OH H C OH Na amalgum, H 2SO4 H C OH CH2OH CH2OH Ribose 77 Ribitol CHO CH2OH H C OH HO C H H C OH H C OH H2 Na amalgum, H 2SO4 H C OH HO C H H C OH H C OH CH2OH CH2OH Glucose Sorbitol CH2OH CH2OH H C OH C=O HO C H H C OH H C OH CH2OH Fructose 78 CH2OH H2 Na amalgum, H 2SO4 HO C H H C OH HO C H OR HO C H H C OH H C OH H C OH CH2OH CH2OH Sorbitol Mannitol Cyclitol ( inositol) It is a cyclic hexa hydric alcohol derived from glucose. A member of vitamin B complex. OH 3 H 4 OH H OH 5 H Inositol 79 OH OH 2 H H 6 OH 1 H 3- Deoxysugars Def:They are monosaccharides with only one of its hydroxyl groups is replaced by hydrogens i.e. there is only one oxygen missed. Examples : 2-Deoxy-D-ribose is a constituent of DNA. 80 Fucose :6 deoxy-galactose ( it is a component of glycoprotein 81 4- Amino sugars Def:The hydroxyl group is replaced by an amino group at the C-2 position. Importance :Amino sugars are found in glycosaminoglycans and glycoproteins. Examples : D-glucosamine: It is a constituent of heparin and hyaluronic acid. D-galactosamine: It is a constituent of chondriotin sulphate. Mannosamine It is a constituent of neuraminic acid and sialic acids 82 CH2OH O H H H OH 2 OH H CH2OH H OHH OH OH H NH2 -D-glucoamine 83 H CH2OHO H OHOH H 2 6CHCHOH2O-SO3H 2 OH H HOH HH H 2 OHOH OH H H H HN CNHCH 2 3 - D-galactosamine O N-acetyl-glucosamine OH OH H OO HH 22 6 CH2O HH O-SO 3H 4 OH OHH HN C CH3 H OH H H NH-SO3H O sulfated N N- acetyl-galactosamine sulfated glucosamine galactos 5-Amino sugar acids Def:They are condensation products of amino sugars and some acids Example: Neuraminic acid Discription: It results from a C-C bond between the C-1 of mannosamine and the C-3 of pyruvic acid. Importance of neuraminic acid It is amino sugar acid present in neural tissue. The N-acetyl derivative of neuraminic (NANA) is called sialic acid, which is widely distributed in bacteria and animal systems 84 85 Monosaccharides of Biological Importance 1) Glucose (Dextrose) (Grape Sugar): It is the most important and famous sugar It is the major source of energy in humans and animals. Ingested carbohydrates are absorbed in the form of glucose. It is converted into other sugars in the liver and other tissues Examples : galactose, fructose, ribose and glycogen. 86 2)Galactose: It is synthesized in mammary gland to form the disaccharide lactose (sugar of milk). It can be converted into glucose in the liver. 3)Mannose: It is a constituent of many glycoproteins and aminosugar acids as sialic acid. 4)Fructose (Levulose) (Fruit Sugar): It is present in semen It is a constituent of disaccharide sucrose and polysaccharide inulin. 87 It can be converted into glucose in the liver. 5)Ribose and deoxyribose: They form part of the structural backbone of nucleic acids RNA and DNA. 6)Ribose enters in the structure of high-energy phosphate compounds as ATP, GTP and CTP and also in the structure of coenzymes such as NAD, NADP, FAD and FMN. 7)Ribose phosphate, Ribulose phosphate, Xylulose and sedoheptulose are intermediates in carbohydrate metabolism 88 The sugar found in DNA is (A) Xylose (B) Ribose (C) Deoxyribose (D) Ribulose The sugar found in RNA is (A) Ribose (B) Deoxyribose (C) Ribulose (D) Erythrose 89 Sorbitol is produced by reduction of : (A) Galactose or fructose (B) Glucose or galactose (C) Glucose or fructose (D) Galactose or fructose Glucose on reduction forms (A) Dulcitol (B) Sorbitol (C) Mannitol (D) Mannitol and sorbitol 90 Glucose on oxidation does not give (A) Glycoside (B) Glucosaccharic acid (C) Gluconic acid (D) Glucuronic acid Oxidation of galactose with conc HNO3 yields (A) Mucic acid (B) Glucuronic acid (C) Saccharic acid (D) Gluconic acid 91 Short Questions Discuss shortly: 1. Define asymmetric carbon atom and enumerate properties resulted from its presence. 2. Mention the physiological importances of carbohydrates. 3. optical activity (def,measurement,examples). 4. Classify sugars according to their optical activity. 5. optical isomerism(def,types) 6. Enentiomers (def,examples ) 7. Anomers (def, examples) 92 8.epimers(def, examples) 9.sugar acids (def,types & example for each) 10. sugar alcohol (def & 3 examples ) 11.Deoxy-sugar ( def & 2 different examples and the importance of each one ) 12.Amino acid sugar (def,example). 13.Enumerate the products of hydrolysis of sialic acid. 14. Enumerate monosacharides of biological importance 93 GREAT THANKS Ayman Elsamanoudy 10/13/2014 Ahmed A.Albadry 94