Carbohydrate Chemistry PDF

Carbohydrate Chemistry Presented By Dr Mai Abdelaziz Gouda  Items to be Covered: 1. Types of Chemical Bonds 2. Introduction 3. Monosaccharides (Aldoses, Ketoses) 4. Isomerism 5. Monosaccharide Derivatives  Types of Chemical Bonds  Covalent bond: Invo...

Carbohydrate Chemistry Presented By Dr Mai Abdelaziz Gouda  Items to be Covered: 1. Types of Chemical Bonds 2. Introduction 3. Monosaccharides (Aldoses, Ketoses) 4. Isomerism 5. Monosaccharide Derivatives  Types of Chemical Bonds  Covalent bond: Involves sharing of electron pairs between atoms. Being the strongest bonds present in different molecules, high energy is needed to break covalent bonds.  Non-Covalent bonds: It does not involve the sharing of electrons. There are four principle kinds of non-covalent forces: 1. Ionic interactions 2. Hydrophobic interactions 3. Hydrogen bonds 4. Van der Waals forces  Introduction  Carbohydrates Cn(H2O)n, commonly known as sugars, (also called saccharides) are molecular compounds made from just three elements: carbon, hydrogen and oxygen.  They are polyhydroxyalcohols with a functional aldehyde or keto group.  BIOMEDICAL IMPORTANCE of Carbohydrates:  Carbohydrates have important structural and metabolic roles.  Glucose is the most important carbohydrate as most dietary carbohydrate is absorbed into the blood stream as glucose.  BIOMEDICAL IMPORTANCE of Carbohydrates: 1- Energy source for plants and animals (glucose): One of the major source of energy in cell. 75% of energy in cell comes from CHO. 25% from others (fats) 1 g CHO =4 K.calories 1 g protein =4 K.calories. 1 g lipid =9K.calories. Why body not use lipid as major energy source instead of CHO?  BIOMEDICAL IMPORTANCE of Carbohydrates: 2- Cell membrane components: eg. Glycolipid and glycoprotein. 3- Form structural tissues in plants and in microorganisms: eg. (cellulose) 4- Glucose is the precursor for synthesis of all other carbohydrates in the body:  Galactose in lactose of milk.  Glycogen for storage of energy in animals, & Starch in plants.  Classification of Carbohydrates  Carbohydrates can be classified according to: The number of sugar units (monosaccharides, disaccharides, oligosaccharides & polysaccharides). The number of carbons they contain (e.g., pentoses, hexoses). Their carbonyl group (aldo- or ketosugars). Classification of Carbohydrates  Monosaccharides According to the number of carbons, it is divided into: - Trioses: contain 3 carbons. - Tetroses: contain 4 carbons. - Pentoses: contain 5 carbons. - Hexoses: contain 6 carbons. According to the presence of aldehyde or ketone group, they are divided into: - Aldoses - Ketoses. Ketone (or Ketol) group in Aldehyde group in ketoses aldoses  Aldoses: 1. Aldotrioses: contain 3 carbons (Examples:Glyceraldehyde) 2. Aldotetroses: contain 4 carbons. (Examples: Erythrose) 3. Aldopentoses: contain 5 carbons. (Examples: Ribose and Xylose) 4. Aldohexoses: contain 6 carbons. (Examples: Glucose and Galactose) Aldoses:  Ketoses: 1. Ketotrioses: contain 3 carbons (Example: Dihydroxyacetone ) 2. Ketotetroses: contain 4 carbons. (Examples: Erythrulose) 3. Ketopentoses: contain 5 carbons. (Examples: Ribulose and Xylulose) 4. Ketohexoses: contain 6 carbons. (Example: Fructose) Ketoses:  MONOSACCHARIDES Aldose Ketose Triose (C3) Glyceraldehyde Dihydroxyacetone (parent- mother) Tetrose (C4) Erythrose Erythrulose Pentose (C5) Ribose & Xylose Ribulose & Xylulose Hexose (C6) Glucose, Galactose, Fructose Mannose  Isomerism  Isomersare compounds having the same molecular formula but differ in structural formula. 1. Enantiomers:  Isomer compounds which are mirror image to each other.  Example: D- glucose and L-glucose 2. Epimers:  Isomers which differ in the configuration around one carbon only.  Examples: D-Glucose and D-mannose are epimers at C2.  D-Glucose and D-galactose are epimers at C4. 3. Aldose-Ketose Isomers:  Isomers which differ in their functional groups.  Examples: Glucose and Fructose.  Forms of Isomerism of Monosaccharides Type of isomer Difference Examples Aldose ketose Functional groups Glucose & Fructose (Functional (different- 1C group) Functional) Epimers only around 1carbon - Glucose & (different- 1C not Mannose (C2) Functional) - Glucose & Galactose (C4) Enantiomers Mirror image D-glucose & (Same- all C) L-glucose  Monosaccharide Derivatives 1-Sugar acids 2-Sugar alcohols 3- Deoxy Sugar 4- Amino Sugar 5- Ester formation 6- Glycosides  Monosaccharide Derivatives 1- Sugar acids a) Aldonic acids: Oxidation of aldehyde group.e.g: Gluconic acid b) Uronic acids: Oxidation of primary alcohol group.e.g: Glucuronic acid c) Aldaric acids: Oxidation of both aldehyde and primary alcohol groups.e.g: Glucaric acid  2- Sugar alcohols  It is the Reduction of carbonyl group to alcohol group. Examples:  Glucose Sorbitol  3- Deoxy Sugar  Hydroxyl group is replaced by a hydrogen atom e.g. deoxyribose present in DNA  4- Amino Sugar Amino group (NH2) replaces the hydroxyl group on the second carbon. e.g. glucosamine. Amino sugars are important constituents of glycosaminoglycans (GAGs ) and some types of glycolipids and glycoproteins. Several antibiotics contain amino  5- Ester formation Phosphate esters: e.g. glucose 6-P 6- Glycosides Condensation of sugars with another sugar: e.g. disaccharides, polysaccharides  The Method Example Importance Derivative 1-Sugar Oxidation of 1ry alcohol Glucose → Glucuronic GAGs acids group to acid group (CH2OH→ acid Uronic acids COOH) Galactose → Galacturonic acid 2-Sugar Reduction of carbonyl group Glucose → Sorbitol -Diabetic complication Alcohols to alcohol group (H-C=O → CH2OH) 3- OH group is replaced by H 2-deoxyriboose DNA Deoxysugars atom 4- OH group (2nd C) is replaced Glucosamine 1- GAGs. Aminosugar by (NH2) Galactosamine 2-Glycolipids & s Mannosamine Glycoproteins 3- Antibiotics 5- Ester condensation of sugar with Glucose 6-P Phosphate Ribose 5-P 6-Glycosides condensation of carbonyl C - Di, Polysaccharide of sugar with Another sugar