CHO Chemistry 1 Nora PDF

1 Level 1 Semester 2  Module (Foundation of basic and behavioral sciences)  Instructor Information Contact: Dr. Nora Mostafa Department: Medical Biochemistry and M...

1 Level 1 Semester 2  Module (Foundation of basic and behavioral sciences)  Instructor Information Contact: Dr. Nora Mostafa Department: Medical Biochemistry and Molecular Biology Email: [email protected] Carbohydrate Chemistry Monosaccharides Dr. Nora Mostafa Lecturer of Medical Biochemistry Mansoura Faculty of Medicine  Learning objectives: By the end of the lecture, the students will be able to:  Define and classify carbohydrates.  Identify the major functions of carbohydrates  Define and classify monosaccharides.  Describe the structure of monosaccharides.  Describe monosaccharides of biological importance.  Describe stereoisomers.  List Sugar derivatives.  Definition: Carbohydrates are organic compounds composed of C.H.O. Hydrogen and oxygen are present in the proportion as in water (H2O). Carbohydrates are polyhydroxy aldehydes (CHO) or polyhydroxy ketones.(C=O) Function of Carbohydrates: They serve as energy stores and fuels. They share in the cell membranes structure. Pentose sugars (ribose and deoxy-ribose) contributes in the structure of nucleic acids. They share in the structure of glycoproteins and glycolipids. They play important roles in cell recognition. Classification: 1. Monosaccharides (‘simple’ sugars): the simplest unit of CHO. 2. Disaccharides: 2 monosaccharide units. 3. Oligosaccharides: 3-10 units of mono-saccharides and their derivatives. 4. Polysaccharides (glycans): more than 10 monosaccharide units and/or their derivatives. Monosaccharides: Are carbohydrates contain only one sugar unit and cannot be hydrolyzed into smaller units. General formula : CnH2nOn They are further classified according to: 1. Number of carbon atoms. 2. The active sugar (carbonyl) group whether aldehyde or ketone. Cyclic structure of monosaccharides 2 formulas were postulated: Hemiacetal structure (Fischer formula). The ring structure (Haworth formula).  Stereoisomers Asymmetric C.A.: Def.: carbon atom attached to four different groups They are compounds having the same structural formula but a different arrangement of atoms in the molecule in space and different properties. Types of Stereoisomerism: 1. Enantiomers (D/L isomers):  Due to the presence of asymmetric carbon atoms. ▪ Mirror image isomers. ▪ All carbons are mirror images but D & L configuration is named according to H – OH orientation in the pre-last C. 2. Anomers (α / β) isomers: ▪ These are isomers that differ in position of OH group at the anomeric carbon atom (it is the asymmetric carbon atom obtained form active sugar group i.e. C1 in aldose and C2 of ketose). 3. Epimers: ▪ In which the difference is in the configuration around one C atom other than the carbonyl C. D-Glucose and D Galactose are C4 epimers while D-Glucose and D-Mannose are C2 epimers. 4. Aldose / ketose isomers: ▪ Two isomers have the same molecular formula but differ in aldehyde or ketone groups e.g. glucose & fructose, ribose & ribulose.  Monosaccharides of Biological Importance: 1. Glucose (Dextrose, Grape sugar): Major source of energy Absorbable form of ingested carbohydrates Converted into other sugars e.g.: Galactose (in mammary gland) Fructose (in seminal vesicles) Ribose (in many tissues). 2. Fructose ( Levulose, Fruit sugar): Present in the semen (seminal vesicles). Formation of Disaccharide →Sucrose Formation of Polysaccharide → Inulin Converted to → Glucose in the liver. 3. Galactose: It is present in the mammary gland. It enters in the formation of Disaccharide (Lactose; milk sugar), Glycolipids & Glycoproteins. It can be converted into Glucose in the liver. 4. Ribose and Deoxy-ribose: enters in the structure of RNA (ribose) and DNA (deoxy ribose). and ATP (high E phosphate compound ). Sugar Derivatives: 1. Sugar Acids: a. Aldonic acids  Due to oxidation of the carbonyl group to carboxylic group.  Gluconic acid is formed from glucose by the effect of glucose oxidase enzyme Clinical Correlates: The oxidation of glucose by glucose oxidase is a highly specific test for glucose used to measure the amount of glucose in urine and in blood using test strips. b- Uronic acids:  Due to Oxidation of the last carbon. e.g. D-Glucuronic acid from D-Glucose c- Aldaric acids (Saccharic acid; Dicarboxylic acid) result from oxidation of both the carbonyl carbon and the last hydroxyl carbon e.g. D-Glucaric acid from D-glucose N.B.: L-ascorbic acid (vit. C) is a sugar acid. 2. Sugar alcohols (Alditols): - Due to reduction of aldoses and ketoses at the carbonyl carbon. - e.g.: Glucose → Sorbitol Mannose → Mannitol Fructose → Sorbitol and Mannitol 3. Deoxy-sugars: Monosaccharides with one oxygen missed (one OH group replaced by H) e.g.: D-Ribose →2-Deoxy-D-ribose 4. Amino-sugars: The hydroxyl group (OH) is replaced by an amino group (NH2) at the C2 position. e.g. D-Glucose D- Glucosamine D-Galactose D- Galactosamine 5. Amino-sugar acids: condensation products of amino sugars and some acids. Example: Neuraminic acid (Mannosamine + Pyruvic acid). It is found in neural tissues The aldose sugar is a) Glyceraldehyde b)Ribulose c)Erythrulose Answer: a d) Dihydoxyacetone e) Xylulose A pentose sugar is a) Dihydroxyacetone b) Ribulose Answer: b c) Erythrose d) Glucose e) Fructose Answer: a Answer: c Sugar found in DNA is a) Xylose b) Ribose Answer: c c) Deoxyribose d) Ribulose Sugar alcohol is a) Mannitol b) Trehalose Answer: a c) Xylulose d) Arabinose Galactose and Glucose are: a) Epimers b) Anomers Answer: a c) Ketose- Aldose isomers d) Enantiomers  References Chatterjea textbook of Medical Biochemistry, 8th edition, 2012. BRS Biochemistry, Molecular Biology and Genetics, 5th edition, 2010. Vasudevan textbook of Biochemistry for Medical students, 6th edition, 2011. Mark′s essentials of Medical Biochemistry, a clinical approach, 2nd edition, 2015. Bhagavan essentials of Medical Biochemistry with clinical cases, 2nd edition, 2015.