DNA is the largest macromolecule in the organisms. It is a long, double chain of deoxy- ribonucleotide, or deoxyribotide units. The two deoxyribonucleotide chains are twisted around a common axis to form a right-handed double helix (spiral) that encloses a cylindrical space in it. Each deoxyribonucleotide unit, in turn, consists of three different molecules .