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 mnemoic device to remember the
difference is that the "Pyramids were CUT
from stone."
Figure © 2012 TA Brown, Introduction
to Genetics (1st ed.); additional
text © 2014 by Steven M. Carr