Which bases are categorized as Purines?

Purines are one of the two categories of nitrogenous bases found in nucleotides, which are the building blocks of DNA and RNA. There are two primary purines: adenine and guanine. These bases are characterized by their two-ring structure, which distinguishes them from pyrimidines, the other category of nitrogenous bases that consists of a single-ring structure.

Understanding the structure of purines is essential in genetics and molecular biology because they play critical roles in the formation of nucleic acids. Adenine pairs with thymine in DNA and with uracil in RNA, while guanine pairs with cytosine in both DNA and RNA. This pairing is crucial for the stability of the DNA double helix and for the proper functioning of RNA during protein synthesis.

The other answer choices contain bases that do not fall into the purine category. For example, cytosine and thymine are both pyrimidines, which have a distinct single-ring structure. Thymine is specific to DNA, while uracil replaces thymine in RNA. Thus, recognizing the difference between purines and pyrimidines is vital for understanding the structure and function of genetic material.