“The nucleotides found in cells are derivatives of the heterocyclic highly basic, compounds, purine and pyrimidine.”

“The purine and pyrimidine bases in cells are linked to carbohydrate and in this form are termed, nucleosides.”

“Conversely, the reaction of purine and pyrimidine nucleobases with alkylating and oxidizing agents generally results in site-specific cleavage.”

“The rearrangement of cross-conjugated mesomeric pyrimidines has been extensively studied.”

“Purines and pyrimidines are considered as complex molecules themselves because they are never synthesized as such in vivo.”

“Both of these products involve dimerization of adjacent pyrimidines on the same DNA strand.”