is an organic compound
, similar to benzene
, but with a heterocyclic ring
: two nitrogen
atoms taking the place of carbon atoms at positions 1 and 3 relative to each
other around the six-member 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.
, the complement of A is U instead of T:
These hydrogen bonding modes are for classical Watson-Crick base pairing. Other hydrogen bonding modes are available in both DNA
, although the additional 3'-hydroxyl group of RNA
expands the configurations through which RNA can form hydrogen bonds.