Adenine and guanine are purines, cytosine and uracil are pyrimidines. Adenine and guanine are purines, while thymine, cytosine and uracil are pyrimidines. DNA contains four different nitrogenous bases&colon; adenine, guanine, cytosine and thymine. It consists of 4 nucleotides guanine, thymine, cytosine, and adenine. Pyrimidines include thymine, cytosine, and uracil. Py denotes pyrimidine which can be either cytosine or thymine. Treatment of DNA with bisulfite converts cytosine residues to uracil, but leaves 5-methylcytosine residues unaffected. This is because sodium bisulfate catalyses deamination of unmethylated cytosine to uracil. It can cause deamination of the amino groups of Adenine, Guanine and Cytosine. Pyrimidine is a component of the nucleobases cytosine, uracil, and thymine. These are examples of modified cytosine, thymine or uridine. Similarly, deamination of cytosine results in uracil. The three others are guanine, cytosine and thymine. Adenine is deaminated to hypoxanthine, which base pairs to cytosine instead of thymine. Bisulfite sequencing relies on the conversion of every single unmethylated cytosine residue to uracil.