Which bases are classified as purines due to their double-ring structure?

The classification of bases as purines is based on their chemical structure. Purines are characterized by having a double-ring structure, which consists of two fused rings made of carbon and nitrogen atoms. In the context of nucleic acids like DNA and RNA, adenine and guanine are the two bases that fit this description.

Adenine, known for its role in both DNA and RNA, features an amine group attached to its structure, making it vital in various biological processes, including energy transfer (as in ATP) and serving as a building block for nucleotides. Guanine, also present in both types of nucleic acids, has a carbonyl and an amine group, indicating its involvement in genetic information storage and transfer.

In contrast, the other bases—cytosine, thymine, and uracil—are classified as pyrimidines, which are characterized by a single-ring structure. Understanding these classifications is essential for grasping the fundamental composition of genetic material and how these bases interact in forming the DNA and RNA structures.