Into which two groups can the nitrogen-containing bases that form DNA and RNA be classified? What is the criterion used in that classification?
The nitrogen-containing bases that form DNA and RNA are divides as pyrimidine and purine bases.
By the examine of the structural formulae of those nitrogen-containing bases it is possible to realize that three of them, cytosine, thymine and uracil, have only one nitrogenized carbon ring. The others, adenine and guanine, have two nitrogenized associated carbon rings.
Nucleic Acid Review - Image Diversity: pyrimidine bases purine bases