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Abstract
On Feb 28, 1953, a Saturday, [James Watson] was in the lab trying to figure out how the purine and pyrimidine bases of DNA could be made to fit within the helix that DNA appeared to form. Using cardboard cut into the shape of the bases, he began to try different pairing arrangements. In his book The Double Helix, Waston writes, "Suddenly I became aware that an adenine-thymine pair held together by two hydrogen bonds was identical in shape to a guanine-cytosine pair held together by two hydrogen bonds. All the hydrogen bonds seemed to form naturally; no fudging was required to make the two types of base pairs identical in shape." When [Francis Crick] arrived, he quickly saw that this pairing would fit with what they knew about the shape of the helix. "We both knew that we would not be home until a complete model was built in which all the stereochemical contacts were satisfactory", Watson writes. "There was also the obvious fact that the implication of its existence was far too important to risk crying wolf. Thus I felt slightly queasy when at lunch Francis winged into the Eagle to tell everyone within hearing distance that we had found the secret to life."