UVA Virtual Lab: DNA (close-up & do-it-yourself)
© 2003-Present J.C. Bean
Here we provide close-up models of the four base pairs that form the core of the DNA molecule: Adenine (A), Cytosine(C), Guanine(G) and Thymine(T). These attach to the sugar of the helical backbones via the bond at the lower right. To switch between the bases, click the "Change Base" button.

Click the "Toggle Bonds" button once to show "pi electrons." A single pi electron (in need of a bonding partner) appears as bulges on opposite sides of an atom. Pairs of unbonded electron appear as a single fat bulge on one side of an atom. Click the button again to pair single pi electrons on neighboring atoms into "pi bonds." Click the button a final time to show how nitrogens with three single bonds flatten as unbonded electron pairs are drawn into the ring′s pi bonds. To move a model, slowly drag your mouse across it.

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