n. (Abbr. A)
A purine base, C5H5N5, that is the constituent involved in base pairing with thymine in DNA and with uracil in RNA.
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.