Franklin, Rosalind Elsie (1920–1958)
Deoxyribonucleic acid, or DNA, carries the inherited information in the genes of most living things. In the early 1950s scientists realized that the key to finding out how this information was stored and reproduced lay in the structure of DNA's complex molecules. Rosalind Franklin took X-ray photographs that gave two rival scientists, JAMES DEWEY WATSON and FRANCIS HARRY COMPTON CRICK, the clues they needed to work out the structure of DNA.
Rosalind Franklin was born on July 25, 1920, in London. Her father, Ellis, was a well-to-do banker, and her mother, Muriel, did volunteer social work, while raising five children. Rosalind decided at age 15 that she wanted to be a scientist. Her father objected, believing like many people of the time that higher education and a career made women unhappy, but she finally overcame his resistance. She studied chemistry at Newnham, a women's college at Cambridge University, and graduated in 1941.
As a way of helping her country during World War II, Franklin became assistant research officer at the Coal Utilization Research Association (CURA). She studied the structure of carbon molecules, introducing, according to one professor, “order into a field which had previously been in chaos.” She turned some of this work into the thesis for her Ph.D., which she earned from Cambridge in 1945.
Seeking new challenges, Franklin went to work for the French government's central chemical research laboratory in 1947. Friends later said that her three years there were the happiest of her life. She enjoyed an easy camaraderie with her coworkers, chatting at cafis and on picnics. She also learned the technique of X-ray crystallography, to which she would devote the rest of her career.
Many solid materials form crystals, in which molecules are arranged in regular patterns. In 1912 a German scientist named Max von Laue found that if a beam of X-rays is shone through a crystal, some of the rays bounce off the crystal's atoms, whereas others pass straight through. When photographic film, sensitive to X-rays, is placed on the far side of the crystal, the resulting photograph shows a pattern of black dots that can reveal important facts about the three-dimensional structure of the molecules in the crystal.
Chemists eventually also found ways to use X-ray crystallography on amorphous compounds, which did not form obvious crystals. Most of the complex chemicals in the bodies of living things are amorphous compounds. Molecular biologists were beginning to realize that the structure of these compounds revealed much about their function, and crystallography was a promising tool for revealing that structure. One of the molecules about whose structure scientists were most curious was DNA.
Scientists knew that the DNA molecule consisted of several smaller molecules. It had a long chain, or “backbone,” made of alternating molecules of sugar and phosphate (a phosphorus-containing compound). Four different kinds of other molecules called bases were attached to the backbone. No one knew, however, whether the chain was straight or twisted, how the bases were arranged on it, or how many chains were in each molecule. Franklin and Maurice Wilkins, the researcher with whom she worked at King's College, hoped that Franklin's X-ray photographs would provide this information.
Franklin photographed two forms of DNA, a “dry,” or crystalline, form and a “wet” form that contained extra water molecules. No one had photographed the wet form before. At the time Franklin was not sure which type gave the more useful information. She took an excellent photograph of the wet form in May 1952, but she put it aside in a drawer and continued working with the dry form.
Two Cambridge scientists, a brash young American named James Watson and a somewhat older Briton, Francis Crick, were also trying to work out the structure of DNA. Although Watson saw himself and Crick as competitors of the King's College group, he and Wilkins became friends, and on January 30, 1953, he visited Wilkins at King's College. Without asking Franklin's permission, Wilkins showed Watson the photograph of “wet” DNA that she had made in May 1952. When he saw the photo, Watson wrote later, “My mouth fell open and my pulse began to race.” He hurried back to Cambridge to describe the photo to Crick.
To Watson the “GillSans Light”–shaped pattern of dots in Franklin's photo showed clearly that the DNA molecule had the shape of a helix. On the basis of this and other evidence, he and Crick concluded, as by this time Franklin also had, that the molecule consisted of two helices twined around each other. The backbones were on the outside and the bases stretched across the center. In other words, the molecule was shaped like a spiral staircase or a twisted ladder with the bases as steps or rungs.
Watson and Crick published a ground-breaking paper on the structure of DNA in Britain's chief science journal, Nature, on April 25, 1953. Neither then nor later did they fully credit Franklin for the important part her photograph had played in their discovery, and Franklin herself probably never realized its role. By the time the Cambridge scientists' paper appeared, she was no longer working on DNA. She had moved from King's College to Birkbeck, a college of the University of London, and was beginning an X-ray study of a common plant virus, the tobacco mosaic virus. Almost nothing was known about the structure of viruses at that time. Franklin drew on her crystallography studies to make a model of the tobacco mosaic virus, which was exhibited at the 1957 World's Fair in Brussels. The virus's inherited information was carried in ribonucleic acid (RNA), a chemical similar to DNA. Franklin showed that the RNA molecule was also a helix.
In 1956 Rosalind Franklin discovered that she had ovarian cancer. The cancer proved untreatable, and she died of it on April 16, 1958. Four years later Watson, Crick, and Wilkins shared the 1962 Nobel Prize in physiology or medicine for their work on DNA. Supporters and critics still debate whether she would or should have been included if she had lived.