Introduction - This script shows a G-C and a A-T base pair. Scroll down until the text corresponding to the view is visible.
Here are two nucleotide base pairs (G-C and A-T) in a DNA duplex. The bases are held together by hydrogen bonds (green).
Here is another view.
Note how the bases stack on top of one another. In a long polymer, the bases are also buried away from water.
Here is a G-C base pair with 3 hydrogen bonds.
Here is a A-T base pair with 2 hydrogen bonds.