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The nucleic acids are biological macromolecules essential for all known forms of life. Together with proteins, 2'-deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) are the most important biological macromolecules of all living things. Their important functions are encoding, transmitting and expressing the genetic information within a biological system which is explained by the central dogma of molecular biology. The nucleic acids are constructed from the repeating units of nucleotides which are made up of a nitrogenous base (purines or pyrimidines), a pentose sugar and a phosphate group. The substructure nucleoside is a combination of a nitrogenous base and pentose sugar.1 Adenine (A) and guanine (G) are the two purine nucleobases whereas thymine (T), cytosine (C) and uracil (U) are the pyrimidine nucleobases. The nucleic acid structures differ in the sugar part of nucleotides where DNA contains 2'- deoxyribose while RNA contains ribose sugar. The two nucleic acids are differentiated on the basis of nucleobase composition. The heterocyclic bases adenine, guanine and cytosine are common in both DNA and RNA while thymine is present in DNA and uracil occurs in RNA. In 1953, Watson and Crick proposed that the molecular architecture of DNA consists of two helical chains each coiled round the same axis with a right handed twist.2 The phosphodiester group is joined to the ß-D-deoxyribofuranose residues through 3'-5' linkages forming a helical chain where they are pointed to outside of the helix (Figure 1.2). The two DNA strands are held together by specific hydrogen bonds between Watson-Crick base pairs (A:T & G:C) to form antiparallel double helical structure.
