The photocatalytic degradation of two components of DNA and RNA, cytosine (C4H5N3O) and uracil (C4H4N2O2) differing only by the presence of an amine or a carbonyl group was investigated in the presence of UV-irradiated TiO2 aqueous suspensions. The adsorption in the dark and under UV-A conditions, the photolysis, the kinetics of degradation, the fate of nitrogen and the identification of some intermediate products were investigated. The impact of pyrimidine cycles on the coverage of TiO2 under UV-A, the effect of NH2 substituent on the oxidation products and mineralization and the importance of carbonyl and amine groups on the fate of nitrogen atoms were evaluated. Electronic density was used to propose a possible chemical pathway. The comparison of the disappearance and mineralization rates in the photocatalytic process was discussed. (C) 2014 Elsevier B.V. All rights reserved.