What is Biochemical Composition

As life evolved on this planet, nature selected only a few elements, and life eventually came to be based essentially on carbon compounds. Out of the nearly 50 or so elements present in most living organisms; six elements, namely, oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus, constitute nearly 99 per cent by weight of a living organism. One of the reasons for nature's selection of carbon in all life forms, could be that carbon forms a wide range of complex organic compounds. Potassium, sodium, chlorine and magnesium account for nearly 0.8%, and the other elements are present in very small amounts (0.2%), and are called trace elements. The distribution of elements in a living organism is given in Table. There is a remarkable similarity in the nature of the chemical substances that are present in all living organisms. Water constitutes nearly 60% of the weight of the living organisms, and is rightly called the "solvent of life", as it is the principal medium in which all cellular reactions occur. The rest, i.e., the dry weight of the cells, comprises proteins, lipids, nucleic acids and carbohydrates. You will study in other units of this block, more details about these essential biomolecules. Table 1.2 gives you the average chemical composition of a cell.