The study of biochemistry is essential to understand basic functions of the body. This will give information regarding the functioning of cells at the molecular level. The proteins are of paramount importance for biological systems. The main role of amino acids is in the synthesis of structural and functional proteins. Unlike carbohydrates and fats, there is no storage form of proteins in the body. The dietary proteins are denatured on cooking and therefore more easily digested. Carbohydrates are the main sources of energy in the body. Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source. Protein is found in every cell of our body. One-fifth of an adult’s total body weight is protein. Lipids, more commonly known as fats and oil, are integral part of our food. Vitamins may be defined as organic compounds occurring in small quantities in different natural foods and necessary for growth and maintenance of good health in human beings and in experimental animals. The absorption of amino acids occurs mainly in the small intestine and is an energy requiring process. Other topics discussed are urea cycle, glycolysis, gluconeogenesis, metabolism of ketone bodies, enzymology: general concepts and enzyme kinetics, fat-soluble vitamins (A, D, E and K), and water-soluble vitamins.