If a nitrogenous base is composed of two of these rings, it is known as a purine, but if it is only composed of one ring, it is called a pyrimidine. Purines and pyrimidines naturally bind to one ...

The purine structure consists of a pyrimidine ring (positions 1 to 6) fused to an imidazole ring (positions 7 to 9). Adenine and guanine, the two most common purines in DNA and RNA, share this core ...

The pyrimidines, thymine (DNA), uracil (RNA), and cytosine are shown on top while the purines, adenine and guanine, are shown at the bottom. (Image: adapted from Wikimedia Commons, public domain) The ...