Introduction DNA (deoxyribonucleic acid) is a biological polymer that stores hereditary information in almost all living organisms. Each strand of DNA is a pattern for duplicating new strands of DNA, so, when cells divide, each new cell gets an exact copy of the DNA from the previous cell. DNA is composed of two strands of repeating units called nucleotides which are entwined in the shape of a double helix. Each DNA strand is 2.2 to 2.6 nanometres wide. Individual DNA molecules can contain hundreds of millions of nucleotides and can be several mm long. Each nucleotide is composed of a nucleobase, a sugar residue and a phosphate group. The nucleobases, adenine (A), cytosine (C), guanine (G) or thymine (T), interact (base pair) with a particular nucleobase in an opposing strand of the double helix by hydrogen bonding interactions; A pairs with T and C pairs with G. The sugar residues are joined together by negatively charged phosphate groups; which form phosphodiester bonds between the 5’ and 3’ hydroxyl groups of each sugar residue. The DNA double helix is stabilized primarily by electronic interactions between the nucleobases and Watson- Crick base pairs (hydrogen bonds) between the nucleobases in the opposing strands.