Nitrogenous bases in DNA
C &
T are single-ringed pyrimidines A &
G are double-ringed purines. Note that the main
purine ring is a a pyrimidine ring, with
the same numbering system, and the secondary rings are
identical. The attachment of NH2 , CH3,
and C=O groups makes each base unique. Compare the
structure of thymine with that of uracil,
which is a pyrimidine base found in RNA.
A mnemonic device to remember the
pyrimidines is that the "Pyramids were CUT
from stone."
Figure © 2012 TA Brown, Introduction
to Genetics (1st ed.); additional
text © 2024 by Steven M. Carr