For decades the Eagle was the local pub for scientists from the nearby Cavendish Laboratory at Cambridge University. It was here on 28 February 1953 that Francis Crick and James Watson first announced their discovery of how DNA carries genetic information.

The Eagle Inn has a long history as a significant part of the Cambridge scene. Some of its timbers as well as its name go back to the 16th century. During the great era of the stage coach, visitors rolled in underneath its arch after a long day’s journey up from London.

Political parties got together here for dinners and junketing. The property was acquired by neighbouring Corpus Christi College, and in the twentieth century the accommodation was taken over as student lodgings. The pub occupied rooms at the back of the yard, where locals, visitors and students enjoyed its traditional atmosphere. During World War II American servicemen based in the area gathered in the bar, and wrote names and service numbers on the ceiling in smoke – now preserved under varnish.

Science in Cambridge was something of a late starter. Despite the powerful work of Newton, and other celebrated individuals, it wasn’t until 1874 that the University had its own laboratory of physical science, the Cavendish. The Laboratory was built in Free School Lane, on a corner of land that had been in turn a friary, a private house and the University Botanic Garden.

By the 1950s it had long been famous for pioneering work on the structure of the atom. (Look for the grey plaque to J J Thomson in Free School Lane.) It had also become, in 1947, the temporary home of a Medical Research Council Unit, researching haemoglobins. Francis Crick joined the Unit in 1949, having shifted his interests from physics to chemistry and thence to biology. Two years later a young American biologist, James Watson, joined the team. He had attended a conference that year, 1951, in Naples at which he had seen x-ray diffraction pictures of DNA. DNA (deoxyribonucleic acid) was the subject of the moment for biologists looking at molecular structure. It was realised that somehow in the DNA was the mechanism by which living cells replicated. The work of Linus Pauling in America and of Maurice Wilkinson at King’s College London (who had shown the x-ray picture) was moving towards identifying the precise structure: possibly a helix, but what were the components, how did they fit together and how could the form reproduce itself?

Watson and Crick found themselves sharing an office in the Cavendish and an enthusiasm for this puzzle. Drawing together the clues from published research, they also made contact with Wilkinson again, and the work being done by Rosalind Franklin. Franklin, a Cambridge graduate, was working in Wilkinson’s team at King’s, but the relationship was an unhappy one, lacking the constructive collaboration that Watson and Crick enjoyed. She was concentrating on x-ray diffraction photography to examine the structure of DNA, and described her findings at a colloquium in November 1951. On this basis, Watson and Crick constructed a model of the structure. When they invited her to see it, Franklin pointed out a number of errors. Watson had not remembered her findings accurately enough.

There was a pause of several months until information from other experiments reached them, and they returned to considering how the chemicals in DNA - adenine, thymine, guanine and cytosine, or A, T, G and C could fit the information they had. Further photographs from King’s helped. They showed more clearly the size of the molecules and the helical construction. Watson pursued the idea of pair bondings that might fit the two-chain helical structure deduced by Crick. With the physical aid of cardboard cut-outs a possible pattern emerged, which they constructed in a model as a double helix. Everything fitted and every condition was answered.

On 28 February 1953 Crick announced dramatically in the Eagle pub that they had found the secret of life. The more formal presentation of their results, with those of Wilkinson and Franklin, appeared in Nature in April 1953. Their conclusion was expressed very modestly:

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”

In 1962 Watson, Crick and Wilkinson were awarded the Nobel Prize for Medicine “for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material”. (Rosalind Franklin had died of cancer in 1958, and as the Prize is never given post-humously did not share the credit that was her due.) Their work initiated a flood of further research round the globe to read in detail the secrets of the code of life.

The MRC Unit moved out of the Cavendish to the School of Medicine where it became the MRC Laboratory of Molecular Biology. A large model representing the double helix can be seen through its window, at the building on the Addenbrooke’s site.

Professor Watson unveiled another representation of the double helix in November 2005 in the grounds of Clare College.