Which of the following are the two pyrimidines present in DNA?

In DNA, pyrimidines are characterized by their single-ring structure and are essential components of the nucleotide building blocks of DNA. The two pyrimidines found in DNA are cytosine and thymine.

Cytosine plays a crucial role by pairing with guanine, a purine, through triple hydrogen bonds, contributing to the stability of the DNA double helix. Similarly, thymine pairs with adenine through double hydrogen bonds, ensuring the accurate transmission of genetic information.

In contrast, adenine and guanine are purines, which are identified by their double-ring structure, making them distinct from the pyrimidines. Thus, options mentioning purines instead of pyrimidines would not be accurate. The pairing of cytosine with thymine highlights the complementary nature of DNA structure, which is fundamental to its function in heredity and protein synthesis.