What distinguishes purines from pyrimidines?

Purines are distinguished from pyrimidines primarily by their structure and size. Purines, which include adenine and guanine, are characterized by a larger double-ring structure. This two-ring configuration allows purines to bind effectively with pyrimidines, which possess a single-ring structure. The larger size of purines compared to pyrimidines facilitates the formation of stable base pairs in nucleic acids like DNA and RNA.

The statement about purines being larger and having two rings accurately captures the key distinction between these two classes of nitrogenous bases in nucleic acids, emphasizing their structural differences which are crucial for their roles in genetic coding and functioning. Understanding these distinctions is fundamental in molecular biology and genetics, particularly in the context of DNA and RNA structure and function.