Which of the following are classified as purines?

Purines are one of the two classes of nitrogenous bases found in nucleotides, which are the building blocks of nucleic acids like DNA and RNA. They are characterized by their two-ring structure, which consists of a fused pyrimidine and imidazole ring. The two purines commonly recognized in genetic material are adenine and guanine.

Adenine is a vital component of DNA and RNA, participating in the formation of ATP (adenosine triphosphate), which is essential for energy transfer within cells. Guanine also plays a crucial role in the structure of both DNA and RNA, pairing with cytosine in base pairing interactions. The classification of these two as purines is critical in understanding their structure and function in genetic processes.

In contrast, the other answer choices consist of nucleotide bases that either belong to the pyrimidine family (like cytosine, thymine, and uracil) or do not represent recognized base pairs in nucleic acids. Pyrimidines have a single-ring structure and include cytosine, thymine (found in DNA), and uracil (found in RNA). Therefore, only adenine and guanine are classified as purines, making the selection of adenine and