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Life in the shape of a corkscrew

50 years ago, James Watson and Francis Crick revealed the structure of DNA

An article of only 980 words, published in the issue of Nature of April 25th 1953 and a little note in the News Chronicle newspaper announced officially what English physicist Francis Crick had spread about, without any care, two months previously. Right after having successfully assembled a three dimensional model of DNA, deoxyribonucleic acid, with the American zoologist James Watson, Crick told the news to anyone willing to listen at The Eagle pub in Cambridge, England. “We have discovered the secret of life”. Actually, he and Watson had discovered the real structure of DNA, something fundamental for understanding how it works.

At first sight, the success of the pair seemed improbable. Watson was a prodigy. He began to study zoology at the age of 15, at the University of Chicago. He became a bachelor at 19, and a doctor at 22. Although he was equally brilliant, Crick had followed an erratic trajectory. In 1951, when Watson found him in Cambridge, Crick was 35 years old and had not yet finished his doctorate, delayed on account of the Second World War, and he had already followed several lines of research, without tarrying in any of them. Chance brought the two together at the Cavendish Laboratory, when both were intrigued with the mysteries of DNA. Another two scientists from King’s College, in London, Maurice Wilkins and Rosalind Franklin, were also at work on the subject.

They produced photographic films of a DNA molecule, which showed a cross-shaped pattern formed by the diffraction of X-rays, and gave a photogram for the pair from the Cavendish, in January 1953. Crick’s calculations had already shown that the DNA molecule ought to have a helicoidal shape, like a corkscrew, and the film confirmed this idea. It so happened that there were other scientists in the race to unveil the structure of DNA. The one who came nearest to the solution was Linus Pauling, working in the United States, but there was Alexander Todd, a chemist from Cambridge, who identified the bases of adenine (A), guanine (G), thymine (T) and cytosine (C).

An American, Erwin Chargaff, had discovered that the quantity of A was equal to that of T, and the quantity of G corresponded to that of C in any DNA sample. What was missing was to say how they were arranged. Watson and Crick built three-dimensional models. And, on February 28th 1953, they noticed that an A-T pair, linked by hydrogen bridges, had the same shape as a G-C pair, and these base pairs should form the axis of a structure that had the main support of sugar and phosphate (from the outside). Nine years later, Watson, Crick and Wilkins won the Nobel Prize. Rosalind had died in 1958, before the award. The revelation sparked off a wave of discoveries that crossed the second half of the 20th century and is far from ending.