Atoms: atomic number through space, 74-75 stability

The spacing of approximately 3.4 A between nearly parallel base pairs is readily apparent in the DNA diffraction pattern (see Figure 5.10). The stacking of bases one on top of another contributes to the stability of the double helix in two ways (Figure 5.13). First, adjacent base pairs attract one another through van der Waals forces (Section 1.3.1). Energies associated with van der Waals interactions are quite small, such that typical interactions contribute from 0.5 to 1.0 kcal mol -1 per atom pair. In the double helix, however, a large number of atoms are in van der Waals contact, and the net... 

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