The principle ones are listed in the table at left. UV-C radiation is adsorbed directly by DNA bases. The most frequent alteration resulting from UV-C is dimerization of the rings of adjacent thymines, forming thymine dimers . Alkylating agents are electrophiles that add methyl, ethyl and more complicated alkyl groups to nucleic acid bases. Electrophilic reactants can also be generated by cytochrome P450 oxidation of xenochemicals.
Bulky adducts result.
Some chemicals intercalate between base pairs. Interpretations Human exposure to DNA damaging chemicals increased in the 20th century due to warfare and chemotherapy. The Fenton reaction has been used to cleave DNA at specific sequences. There are other ways in which DNA can be damaged . Changes arising from environmental damage can be repaired .