CHAPTER THREE: BIOCHEMISTRY Chapter 3/p1 CARBOHYDRATES There are three main types of carbohydrates: monosaccharides – these are simple sugars which cannot be broken down to anything simpler. disaccharides – double sugars, yield two monosaccharides on hydrolysis. polysaccharides – complex sugars, yield many simple sugars on hydrolysis. MONOSACCHARIDES Hexoses - glucose, fructose and galactose. All contain 6 carbon atoms. Categorized according to the number of carbons. glucose

Chapter 3/p2 NB. For properties of glucose, fructose and galactose, refer to notes. IDENTIFICATION OF GLUCOSE To test for glucose in the urine which is a strong indication of diabetes, add Benedict’s reagent. Glucose (-CHO) + Cu 2+ + OH - → - COO - + Cu 2 O blue solution red ppt. DISACCHARIDES Sucrose, maltose and lactose. Sucrose – glucose + fructose, found in sugar cane and sugar beet. Maltose – glucose + glucose, malt sugar – hydrolysis of starch. Lactose – glucose + galactose, milk sugar. POLYSACCHARIDES Starch, cellulose, glycogen and dextrin.

Chapter 3/p3 LIPIDS Lipids are organic compounds and in general: insoluble in water. soluble in nonpolar organic solvents such as ether, acetone and carbon tetrachloride. contains carbon, hydrogen and oxygen; sometimes contain nitrogen and phosphorus. yield fatty acids on hydrolysis or combine with fatty acids to form esters. Take part in plant and animal metabolism. FATTY ACIDS Straight – chain organic acids and contain an even number of carbon atoms. Can be either saturated or unsaturated. Saturated fatty acids contain only single bonds between carbon atoms whereas unsaturated fatty acids contain a few double bonds between carbon atoms. Polyunsaturated fatty acids contain many double bonds.

Chapter 3/p4 Unsaturated fatty acids can be subdivided into the following categories: monounsaturated, only one double bond. polyunsaturated – many double bonds. eicosanoids – includes prostaglandins, leukotrienes, prostacyclins and thromboxanes. Linoleic acid is called the nutritionally essential fatty acid – it is essential for the complete nutrition of the body. The absence of the essential fatty acid from the diet of an infant causes loss of weight. CLASSIFICATION OF LIPIDS SIMPLE LIPIDS Simple lipids are esters of fatty acids. Hydrolysis of a simple lipid may be expressed as: simple lipid + H 2 O fatty acid(s) + alcohol hydrolysis

Chapter 3/p5 If the hydrolysis of a simple lipid gives three fatty acids and glycerol, the simple lipid is called a fat or an oil. If the hydrolysis of a simple lipid gives a fatty acid and a high molecular mass monohydric alcohol, the simple lipid is called a wax. COMPLEX LIPIDS Complex lipids on hydrolysis yield one or more fatty acids, an alcohol and some other type of compound. Some examples are phospholipids and glycolipids. Phospholipids undergo hydrolysis as follows: phospholipid + H 2 O fatty acid(s) + alcohol + phosphoric acid + a nitrogen compound hydrolysis

Chapter 3/p6 FATS AND OILS Fats are esters formed by the combination of a fatty acid with glycerol. Unsaturated fats and oils combine with iodine whereas saturated fats and oils will not. The iodine number of a fat or oil is the number of grams of iodine that will react with the double bonds present in 100 g of that fat or oil. The higher the iodine number, the greater the degree of unsaturation of the fat or oil. In general, animal fats have a lower iodine number than vegetable oils. SOAPS Soaps are produced by the saponification of fats, soaps are salts of fatty acids C 17 H 35 COOH + NaOH → C 17 H 35 COONa + H 2 O stearic acid sodium hydroxide sodium stearate, a soap

Chapter 3/p2 WAXES Compound produced by the reaction of a fatty acid with a high molecular mass monohydric alcohol such as ceryl alcohol, C 23 H 53 OH. STEROIDS e.g. cholesterol.

Chapter 3/p8 PROTEINS AMINO ACIDS Building blocks of proteins. An amino acid is an organic acid that has an amine (-NH 2 ) group attached to a chain containing an acid group. Amphoteric compounds, i.e. can react with an acid or base, account for their ability to act as buffers in the blood. At a certain pH, amino acids will not migrate towards the positive or the negative electrode, they will be neutral, i.e. there will be an equal number of positive and negative ions. This point is called the isoelectric point. DIPEPTIDES Proteins consist of many amino acids joined together by what is called a peptide linkage or a peptide bond.