James D. Watson and Francis Crick were the two co-discoverers of the structure of DNA in 1953. They used x-ray diffraction data collected by Rosalind Franklin and proposed the double helix or spiral staircase structure of the DNA molecule. They were, with Maurice Wilkins, awarded the Nobel Prize in Physiology or Medicine in 1962.
Francis and I were running against God, in the sense that we wanted to know what made us human. Both of us had been subjected to religious truths which came by revelation, and we didn't have much acceptance of truths by revelation. We wanted to know really what we were. We both were very curious what life was.
In a sudden burst of insight, Watson and Crick built a model out of brass plates and clamps and other bits of laboratory equipment in 1953. As they worked, they realized that nucleic acids are arranged on a twisted ladder, with two runners made of phosphates and sugars, and a series of rungs made of pairs of organic compounds known as bases. Years later, they won the Nobel Prize for this frenzy of discovery of DNA's double helix.
Major current advances in science, namely genetic fingerprinting and modern forensics, the mapping of the human genome, and the promise, yet unfulfilled, of gene therapy, all have their origins in Watson and Crick's inspired work. The double helix has not only reshaped biology, it has become a cultural icon, represented in sculpture, visual art, jewelry, and toys.
Watson and Crick never enjoyed the easiest of relationships. "I wanted to start my book [The Double Helix] with the sentence, 'I've never seen Francis in a modest mood' but the lawyer wanted me to change it to 'seldom'," Watson laughs.
Drawing on the experimental results of others (they conducted no DNA experiments of their own), taking advantage of their complementary scientific backgrounds in physics and X-ray crystallography (Crick) and viral and bacterial genetics (Watson), and relying on their brilliant intuition, persistence, and luck, the two showed that DNA had a structure sufficiently complex and yet elegantly simple enough to be the master molecule of life.
“It was precisely their lack of preconceived notions that gave Watson and Crick an advantage in ﬂexibility in considering many possibilities that might have been rejected in a more systematic and deliberate approach.”
They also knew that DNA included different amounts of the four bases adenine, thymine, guanine and cytosine (usually abbreviated A, T, G and C), but nobody had the slightest idea of what the molecule might look like.
Watson and Crick took a crucial conceptual step, suggesting the molecule was made of two chains of nucleotides, each in a helix as Franklin had found, but one going up and the other going down. Crick had just learned of Chargaff's findings about base pairs in the summer of 1952. He added that to the model, so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant.
he had a credible model structure of DNA. “Not by logic but serendipity,” as Crick put it, Watson had found base pairing that worked. He was using neither Chargaff’s rules, which, Donohue noted, he was still “cheerfully disregarding,” nor the crystallographic evidence that had moved Crick two weeks before.
Their model served to explain how DNA replicates and how hereditary information is coded on it. This set the stage for the rapid advances in molecular biology that continue to this day.
The structure so perfectly fit the experimental data that it was almost immediately accepted. DNA's discovery has been called the most important biological work of the last 100 years, and the field it opened may be the scientific frontier for the next 100.
What they found was that different letters of the genetic structure could be superimposed on one another without changing anything. Everything had to be equidistant and smooth.
We also know that there are two basic categories of nitrogenous bases: the purines (adenine [A] and guanine [G]), each with two fused rings, and the pyrimidines (cytosine [C], thymine [T], and uracil [U]), each with a single ring.
Inspired by Pauling’s success in working with molecular models, Watson and Crick rapidly put together several models of DNA and attempted to incorporate all the evidence they could gather. Franklin’s excellent X-ray photographs, to which they had gained access without her permission, were critical to the correct solution.
Watson and Crick used stick-and-ball models to test their ideas on the possible structure of DNA. Other scientists used experimental methods instead. Among them were Rosalind Franklin and Maurice Wilkins, who were using X-ray diffraction to understand the physical structure of the DNA molecule.
Francis Crick and I made the discovery of the century, that was pretty clear. We made it, and I guess time has justified people paying all this respect to me in spite of my bad manners.