Crick and Watson were downcast by the news from Peter Pauling that his father appeared
to have solved DNA.
Alternating between bouts of despair and denial - trying to figure out how he could
have beaten them and then deciding that he certainly could not have without seeing
Wilkins and Franklin's x-ray work and then thinking, well, of course, he is Pauling,
so anything is possible - they continued working on the problem themselves. If they
could come up with something independently before Pauling's paper appeared, at least
they might share credit.
This time they added a critical observation. Crick and Watson knew Erwin Chargaff, an acerbic and opinionated Austrian-born biochemist who used chromatography to analyze
the chemical composition of nucleic acids. Chargaff had told them about a simple relationship
he had found between the occurrence of different bases in DNA: adenine and thymine
were present in roughly the same amounts and so were guanine and cytosine. One of
each pair was a larger purine; the other, a smaller pyrimidine.
Chargaff had told Pauling the same thing when they shared a shipboard dining room
during an Atlantic crossing in 1947, but Pauling found Chargaff annoying and ignored
It made all the difference to Crick and Watson. Franklin's criticisms had already
pointed them toward putting the phosphates on the outside of the molecule; now they
had the clue of a one-to-one relationship between the bases on the inside. They began
thinking about helixes in which the purines and pyrimidines lined up somehow down
the core of the molecule.