The pyrimidines, cytosine and uracil, are smaller and have a single ring, while the purines, adenine and guanine, are larger and have two rings.

What are single ringed bases called?

The nitrogenous base is either a double ringed structure known as a purine or single ringed structure known as a pyrimidine. There are five common nitrogenous bases; adenine, guanine, thymine, cytosine and uracil.

Are pyrimidines base pairs?

Pyrimidines are aromatic nitrogen heterocycles with a structure similar to benzene but containing two nitrogen atoms at the 1 and 3 positions of the ring. ... Cytosine and thymine are the two major pyrimidine bases in DNA and base pair (see Watson–Crick Pairing) with guanine and adenine (see Purine Bases), respectively.