Pyrimidines and Pyrimidine Nucleotides Structure of Pyrimidines and Pyrimidine Nucleotides Cytosine, thymine, uracil, and orotate are the most common pyrimidines in nucleotides. In comparison to the typical pyrimidine ring structure, cytosine has oxo (keto) and amino groups at positions 2 and 4, while orotate has oxo groups at positions 2 and 4 and a carboxyl … Read more