Pyrimidine - Definition and Overview

Pyrimidine is a heterocyclic aromatic organic compound, which is similar to benzene and pyridine and that contains two nitrogen atoms at positions 1 and 3 of the six-membered ring.

Three bases of the nucleic acids, namely cytosine, thymine, and uracil, are pyrimidine derivatives. In DNA, these bases form hydrogen bonds with their complementary purines.

purine  pyrimidine
   A         T
   G         C

In RNA, the complement of A is U instead of T:

purine  pyrimidine
   A         U
   G         C

Cytosine

Uracil

Thymine

These hydrogen bonding modes are for classical Watson-Crick base pairing. Other hydrogen bonding modes are available in both DNA and RNA, although the additional 2'-hydroxyl group of RNA expands the configurations through which RNA can form hydrogen bonds.

See also

• Pyrazine, an analog with the nitrogen atoms in positions 1 and 4.
• Simple aromatic rings