Which bases are classified as purine bases?

Purine bases are characterized by their two-ring structure in their molecular composition. In the context of nucleic acids, the purine bases include adenine and guanine. Both of these bases play vital roles in the structure of DNA and RNA, where adenine pairs with thymine in DNA and uracil in RNA, while guanine pairs with cytosine in both types of nucleic acids. Understanding the distinction between purines and pyrimidines, which have a single-ring structure, is essential in molecular biology, particularly when studying the genetic code and various metabolic pathways involving nucleotides.