base can be adenine 1.1.2 The nitrogenouS), or thymine(t) (A), guanine(G), cytosine (uracil(U)in RNA). 1.1.3 The nitrogenous bases are derivatives of two parent compounds, pyrimidine and purine.1.1.2 The nitrogenous base can be adenine (A), guanine (G), cytosine (C), or thymine (T) (uracil (U) in RNA). 1.1.3 The nitrogenous bases are derivatives of two parent compounds, pyrimidine and purine