Biochemistry

CHAPTER 2. CHEMISTRY OF PROTEINS 2.1. BIOLOGICAL ROLE OF PROTEINS Proteins (from the Greek protos - first) form the basis of living matter and play a paramount role in the functioning of any organism. They are nitrogen ­ containing high molecular weight organic compounds (polymers), consisting of amino acids (monomers), which are sequentially interconnected by peptide bonds. Proteins are the most important component of living organisms not only in value, but also in quantitative content in tissues and organs. As a rule, plants contain less protein than animals (Table 2.1). Table 2.1. - Protein content in animal tissues and plants Organs and tissues of animals Protein content % by weight Organs and tissuesn of plants Protein content % by weight Muscle 18-23 Plants' seeds 10-13 Liver 18-19 The stalks 1,5-3 Lungs 14-15 Leaves 1,2-3 Kidney 16-17 Roots 0,5-3 Brain 7-9 Fruit 0,3-1 The main source of nitrogen assimilated by humans are amino acids of food proteins, therefore, proteins are indispensable in the diet (Table. 2.2). Table 2.2 - The most important sources of protein in food proructs Food proructs Protein content % by weight Food proructs Protein content % by weight Milk 2,79-2,82 Eggs 12,7-16,2 Cottage cheese 14,0-18,0 Peas, beans 20,5-21,0 Hard cheeses 23,0-26,0 Bread 6,6-7,6 Meat 11,4-21,1 Potatoes 2,0-2,4 Fish 13,1-21,0 Each protein is unique in its structure and functions. According to their biological role, proteins can be divided into several groups. Catalytic proteins. By biological significance, the central place among proteins belongs to enzymes. All chemical transformations in living organisms are accelerated and regulated by biological catalysts - enzymes. Most of the enzymes studied are simple or complex proteins. 37