Almaaqal University Chemistry of Carbohydrates PDF

Almaaqal University Chemistry of Carbohydrates Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-7  Carbohydrates  Carbohydrates are the most abundant organic molecules in nature.  Carbo...

Almaaqal University Chemistry of Carbohydrates Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-7  Carbohydrates  Carbohydrates are the most abundant organic molecules in nature.  Carbohydrates are formed of carbon, hydrogen, and oxygen atoms with a ratio of 1:2:1 with the general formula Cn(H2O)n.  They are organic substances (polyhydroxy aldehyde or ketone).  Most names for sugars end in -ose. Biomedical importance of Carbohydrates They have a wide range of functions, including: 1. Considered the chief source of energy for most organisms. 2. Acting as a storage form of energy in the body. 3. Serving as cell membrane components that mediate some forms of intercellular communication. 4. Ribose and deoxyribose sugars form part of the structure of RNA and DNA. 5. Major antigens are carbohydrates in nature, e.g., blood group substances  Classification of carbohydrates A-According to the hydrolysis products (no. of individual simple units): 1-Monosaccharides: contain 1 sugar unit (can not be hydrolyzed). Ex: Glucose, galactose , mannose, & fructose. 2- Disaccharides: contain 2 sugar units. Ex: Maltose, lactose & sucrose. 3- Oligosaccharides: contain 3-10 sugar units. 4- Polysaccharides: more than 10 sugar units. Ex: Starch, glycogen & cellulose.  Monosaccharides  They are the simplest units of carbohydrates and the building block.  The general formula is: (CH2O)n, so the name of carbohydrates (carbon+ H2O).  The ratio between carbon & H2O =1  Most of the monosaccharides occurring in mammals are D sugars.  Ex: Glucose , mannose, galactose & fructose.  Classification of monosaccharides I- According to the No. of carbon atoms: 1- Trioses: contain 3 carbon atoms. 2- Tetroses: contain 4 carbon atoms. 3- Pentose: contain 5 carbon atoms. 4- Hexoses: contain 6 carbon atoms. II- According to the functional group: 1- Aldoses: monosaccharides containing aldehyde group (−CH=O). Ex. Glyceraldehyde, erythrose, ribose, glucose, galactose, mannose. II- According to the functional group: NOTE: The mother compound of all aldoses is aldotriose “ glyceraldehyde” 2-Ketoses: monosaccahrides containing ketone group (−C=O). Ex. Dihydroxyacetone, erythrulose, ribulose, fructose. NOTE: The mother compound of ketoses is ketotriose “dihydroxyacetone” Structural formula of aldoses Structural formula of ketoses  Disaccharides  Disaccharides consist of two monosaccharides united together by glycosidic linkage.  Disaccharides are classified into reducing disaccharides and non- reducing disaccharides.  A- Non-reducing Disaccharides  Sucrose: hydrolyzed by sucrase enzyme into Glucose + Fructose  Reducing disaccharides  Lactose: hydrolyzed by lactase enzyme into Galactose + Glucose  Maltose: hydrolyzed by maltase enzyme into 2 Glucose.  3- OLIGOSACCHARIDES These are polymers of 3-10 monosaccharide units. They are not an important source of carbohydrates in the diet for humans as most of them are nondigestible. Ex. oligosaccharides which are constituents of ABO blood group substance, immunoglobulins, and glycolipids and glycoproteins of cell membranes. 4- Polysaccharides  Polysaccharides are composed of more than 10 monosaccharide units linked by glycosidic bonds.  Polysaccharides are nonreducing.  Polysaccharides include homopolysaccharides and heteropolysaccharides.  Polysaccharides: They are Classified in to : Homopolysaccahrides Heteropolysaccahrides (containing only 1 type of ( containing more than 1 type of monosaccharide) monosaccharide) Glucans Fructans Glycosaminoglycans (D-glucose (D-fructose (mucopolysaccharides) units) units) starch inulin Dextrin glycogen cellulose  Classification of carbohydrates B-According to reducing capacity: Reducing sugars Non reducing sugar (contain one free (contain NO free anomeric anomeric carbon atom) carbon) All monosaccharides Sucrose All disaccharides except All polysaccharides sucrose Reducing capacity is defined by the presence of free aldehyde or ketone group.