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Nucleotide constitutes an organic molecule having a composition of a nitrogenous base, pentose sugar and phosphate. The different polynucleotides include DNA and RNA that comprise a chain of nucleotide monomers having varying nitrogenous bases.

The conformation of a nucleotide unit is indicated by the six torsion angles of the sugar phosphate backbone and the torsion angle explaining the base orientation around the glycosidic bond ( the bond connecting C1’ to the base). Purine residues comprise two sterically orientations known as the syn and anti conformation.

The anti conformation of pyrimidines is stable as in the syn conformation, the sugar residues interferes with the pyrimidine’s C2 substituent. So the bases are all in the anti conformation in most of the double-helical nucleic acids.