Carbohydrates

Carbohydrates Composed of carbon, hydrogen, oxygen General formula Cx(H2O)y Two types: simple sugars and condensation polymers Functions: Energy Precursors for metabolic rxns Storage Structural material (plants)

Monosaccharides Simple sugars Soluble in water (glucose, fructose) Classified by number of carbons Contain two or more hydroxyl groups and one carbonyl group Exist in chain or ring form Hydroxyl group in ring form can be either α (projected downward) or β (projected upward)

+ D-fructose α-D-fructose β-D-fructose

Disaccharides Two simple sugars linked together Soluble in water, hydrolysed by acid hydrolysis or enzymes Condensation reaction! Resulting bond: glycosidic link (1-4 link b/c C1 bonded to C4) Lactose: beta-glucose + beta-galatose Maltose: alpha-glucose + alpha-glucose Sucrose: alpha-glucose + beta-fructose

Polysaccharides Long chains of monosaccharide units held together by glycosidic bonds Insoluble in water, ideal for storage 3 common polysaccharides Starch (alpha-glucose), contains amylose and amylopectin, storage carbohydrate in plants (potato, rice, flour) Glycogen (alpha-glucose), animal starch, found in liver, muscles Cellulose (beta-glucose), structural material in plants

amylose amylopectin glycogen cellulose

Starch vs. Cellulose Polymers of glucose Starch: alpha-glycosidic links Cellulose: beta-glycosidic links Different linkage forms uncoiled linear structure w/ alternating glucose monomers: hydroxyl groups form H bonds with hydroxyl of other parallel cellulose Cannot digest cellulose b/c enzyme cellulase not produced in humans and most mammals

Dietary Fiber! Plant material Cellulose, pectin, waxes, lignin Cannot hydrolyze b/c lack cellulase enzyme Why is it important? Prevention! Irritable bowel syndrome Constipation Hemorrhoids Colorectal cancer