Carbohydrate Dr.Gulve R.M.

MONOSACCHARIDE Classification according to type ( Nature of carbonyl group) Aldoses: Presence of aldehyde group (--CHO) e.g. glucose, xylose, ribose. Ketoses: Presence of ketone group (--C=O) e.g. fructose, xylulose, ribulose.

Classification according to number of carbon group ( Length of carbon chain): Bioses :(C2H4O2) -2 carbon atoms in chain. Trioses: (C3H6O3) - 3 carbon atoms in chain. e.g. Glyceraldehydes Tetroses: (C4H8O4) -4 carbon atoms in chain. e.g. Erythrose, Threose Pentoses :(C5H10O5)- 5 carbon atoms in chain. e.g. D-Ribose, D-Ribulose, L-Arabinose, D- Xylose. Hexoses (C6H12O6)- 6 carbon atoms in chain.: e.g. D-Glucose, D-Fructose Heptoses(C7H14O7) -7 carbon atoms in chain:-Sedoheptulose

DISACCHARIDE

POLYSACCHARIDE Starch: Starch is the reserve substances in plant cells. It is polymer of D-glucopyranose unit (D-glucose) having α- 1,4 glycosidic linkage. It consists of mixture of amylose and amylopectin in the proportion of 1:4. Both are high molecular weight compounds. Amylose is linear while amylopectin is branched. Amylose dissolves in hot water but not amylopectin. Amylose contain about 200-500 glucose units which are arranged in the form of a straight chain. Its molecular weight varies from few thousand to about 150,000. Amylose give blue color with iodine .Amylopectin has over 1000 glucose units and molecular weight is about 200,000 to 1,000,000. It has branched structure. Amylopectin consist of glucose units linked by α-1, 4 glycosidic bonds. There are occasional α-1, 6 glycosidic bonds, which cause branching. Amylopectin (branched polysaccharide).Starch on hydrolysis yields lower molecular weight polysaccharides and finally maltose or glucose. Partial hydrolysis of starch results in substances called ‘dextrin’ (highly branched core).The enzyme which hydrolyze starch are α-amylase and β-amylase. Starch is present in seed grains, potato, and wheat.

Cellulose: The most abundantant structure of polysaccharide is cellulose. Cellulose is a linear, homopolysaccharide composed of D-glucopyranose units linked β- 1, 4 glycosidic linkage. It is the most important cell wall component of plants. It is also found in few microorganisms and lower organisms. It is not digested by digestive enzymes of man and other animals. Snail secretes a cellulase that hydrolyzes polymer. In contrast to starch and glycogen cellulose is insoluble in ordinary solvents and is not hydrolyzed by boiling dilute acids. It gives no color with iodine. Β- 1, 4 linkage of cellulose are highly resistant to acid hydrolysis. Partial hydrolysis yields cellobiose, cellotriose. Bacteria found in rumen cattle of and other animals can also hydrolyze cellulose.

Chitin: Chitin is a homopolymer of N-acetyl glucosamine Chitin: Chitin is a homopolymer of N-acetyl glucosamine. It is structurally polysaccharide. It is important polysaccharide of invertebrates. It is found in the hard exoskeleton of insects and crustaceans and in the cell wall of fungi. It is polyglycane consisting of N- acetyl – D- glucosamine units, connected through β- 1, 4 –glycosidic linkage. Like cellulose it consists of parallel chains of molecules, held together in bundles by hydrogen bonds.

HETEROPOLYSACCHARIDE (Heteroglycans) a) Hyaluronic acid: It is the simplest mucopolysaccharide. It is linear polymer of disaccharides with the repeating units. It consists of D- Glucuronic acid and N- acetyl – D glucosamine linked by β- 1, 3 linkages and between two disaccharide β- 1, 4 glycosidic bonds are present. Hyaluronic acid found in the skin, vitreous humour of the eye, umbilical cord, as the coating around the ovum and in certain bacteria. It acts as cementing substance in connective tissue. Present in the fluid of joints as a good lubricants.

BIOLOGICAL IMPORTANCE OF CARBOHYDRATE Carbohydrates are most important energy source. They are structural component of tissue and play role in regulation of fat metabolism and digestive tract. 1) Store substances as an energy source: Carbohydrates are important energy source in animals. Carbohydrate provides 60% energy of the total energy requirement of man. Glucose is immediate energy source required by tissues. Glucose provides energy to brain and other nervous tissues .Carbohydrates is stored in the body in form of glycogen.100 gram stored in liver and 200 -240 gram in muscle. 2) Structural component: Carbohydrates are important components of some structural materials of living organisms. i) Monosaccharide (ribose and deoxyribose) are important structural constituent of nucleic acids. ii) Coenzyme, flavoproteins and blood group substances, vitamin C (ascorbic acid) are also sugars. iii) Immunopolysaccharide protects the body from attack of microorganisms. Hyaluronic acid is viscous substance present in connective tissue. Heparin presents the clotting of blood. Glucuronic acid present in the liver.