Because there are four naturally occurring nitrogenous bases, there are four different types of DNA nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). Within double-stranded DNA ...

A nucleic acid is a long molecule made up of smaller molecules called nucleotides. Nucleic acids were discovered in 1868, when twenty-four-year-old ... it was a novel type of biological molecule.