Less than a week after he first sat down with the problem, Pauling excitedly wrote a colleague, "I think now we have found the complete molecular structure of the nucleic acids."

During the next several weeks he ran downstairs every morning from his second-story office at Caltech to his colleague Verner Schomaker's office, "very enthusiastic," Schomaker remembered, bouncing ideas off the younger man, thinking aloud as he checked and refined his model.

Then came trouble. Pauling's meticulous right-hand man at Caltech, Robert Corey, made detailed calculations of Pauling's proposed atomic positions and found that the pieces did not fit. In early December, Pauling went back to twisting and squeezing his model. Someone brought up the question of how his model allowed for the creation of a sodium salt of DNA, in which the positive sodium ions supposedly adhered to the negative phosphates. There was no room for sodium ions in his tightly packed core, was there? Pauling had to admit he could find no good way to fit the ions. But that would sort itself out later.

The central problem had reduced itself in his mind to a simple question of making the atoms fit. The biological significance of DNA would be worked out later, he thought; if the structure was right, the biological importance would fall out of it naturally in some way. So he ignored the larger context surrounding the molecule and focused single-mindedly on one thing: finding a way to fit those phosphates into the core.

A week before Christmas 1952, he wrote the organic chemist Alex Todd at Cambridge, "We have, we believe, discovered the structure of nucleic acids. I have practically no doubt. . . The structure really is a beautiful one."