How do purines differ from pyrimidines structurally?

Purines are characterized by their double-ring structure, which consists of two fused rings containing nitrogen atoms and carbon atoms. This structural configuration makes purines larger and more complex molecules compared to pyrimidines, which have a single-ring structure. Examples of purines include adenine and guanine, both of which play essential roles in nucleic acid structure.

The size and shape of purines allow them to pair effectively with pyrimidines (cytosine, thymine, and uracil) in the formation of nucleic acids, contributing to the stability of DNA and RNA. Understanding the structural differences between these two classes of nitrogenous bases is fundamental in biology, particularly in genetics and molecular biology, where the arrangement and pairing of these bases underlie much of the information encoding in living organisms.