So this is base pair number one, base pair number two, base pair number three, and so forth. The red molecules are the guanine, the blue molecules are the cytosine. The green molecules are the adenine, and the orange molecules are the thymine. And because they essentially are located adjacent with respect to one another, we have these hydrogen bonds shown in purple. Now, because we have a distance of 3.4 angstromes between any base pair, and because this distance corresponds to Vander valve forces, that means we have a bunch of London dispersion interaction taking place between our bases. So these bases are basically stacked on top of one another.