Pyrimidine

Pyrimidine is an organic compound, similar to benzene but with two nitrogen atoms taking the place of carbon atoms in the ring. Three bases in nucleic acids, namely cytosine, guanine, and uracil?, are pyrimidine derivatives. In DNA, these bases form hydrogen bonds with their complementary purines.

 purine  pyrimidine

    A         T

    G         C

In RNA, instead of T, U complements A:

 purine  pyrimidine

    A         U

    G         C

These hydrogen bonding modes are for classical [Watson-Crick base pair]?ing. Other hydrogen bonding modes are available in both DNA and RNA, although the additional 3'-hydroxyl group of RNA expands the configurations through which RNA can form hydrogen bonds.

/Talk?