iGen3 02-13aiGen3 02-13b

A+T and G+C pairs have similar structures

The combination of a two-ring purine (A or G) and a single-ring pyrimidine (T or C) forms a base bair (
A+T or G+C ) with three co-planar rings.

A+T has two H-bonds versus the G+C with three .

Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2010 by Steven M. Carr