Carbon is the basic element of organic compounds. Due to its unique properties, carbon occupies the central position in the skeleton to life.
Carbon is tetravalent. It can react with many other known elements forming covalent bonds.
Covalent bonds result when two or more atoms complete their electron shells by sharing electrons. When an electron pair is shared between two atoms, a single covalent bond results. An example is the bond between two hydrogen atoms to from a hydrogen molecule. Covalent bond stores large amount of energy.
When a carbon atom combines with four atoms or radicals, the four bonds are arranged symmetrically in a tetrahedron, and result to give a stable configuration. The stability associated with the tetravalency of carbon atoms makes it a favorable element for the synthesis of complicated cellular structures. Carbon atoms can also combine mutually forming stable, branched or unbanked chains or rings. This ability of carbon it responsible for the vast variety of organic compounds. C – C bonds form a skeleton of organic molecules as shown in Fig. 2.1.
Fig. 2.1 unbranched and branched chains, and ring structure formed by C-C bonds.
Carbon combines commonly with H, O, N, P and S. combinations with these and other elements contribute to the large variety of organic compounds. Carbon and hydrogen bond (C-H bond) is the potential source of chemical energy for cellular activities. Carbon-oxygen association in glycosidic linkages provides stability to the complex carbohydrate molecules. Carbon combines with nitrogen in amino acid linkages to form peptide bonds and forms proteins which are very important due to their diversity in structure and functions.
Large organic molecules (macromolecules) such as cellulose, fats, proteins, etc, are generally insoluble in water, hence they form structures of cells. They also serve as storage for smaller molecules like glucose, which in turn are responsible for providing energy to the body.
Small molecules, such as glucose, amino acids, fatty acids etc. serve either as a source of energy, or as subunits to build macromolecules. Some small molecules are so unstable that they are immediately broken down to release energy e.g. ATP. Such substances serve as immediate source of energy for cellular metabolism.