Solving One of the Mysteries of Life

The familiar double-helix shape of DNA

(National Human Genome Research Institute)

Fifty three years ago today, in the last week of February 1953, a discovery was made at England’s University of Cambridge that would transform the field of science and spur previously unimaginable technological developments.

That week two scientists, James Watson, 24, and Francis Crick, 12 years his senior, successfully completed a working model for the molecule that stores the instructions for life, DNA. Though the two men had been working for years, the major developments in their studies had come fast and furious in the previous weeks, and they were careful to be certain of their success before announcing it publicly. By February 28, however, they were confident enough of their findings to go to lunch at Cambridge’s Eagle Pub and tell the establishment’s patrons they “had found the secret of life.” A more official statement followed not long thereafter, as the two men published a short paper in Nature magazine on April 25 and another, longer essay a month later.

Deoxyribonucleic acid, better known as DNA, is the molecule that houses the information cells need in order to build proteins, which in turn allow the living body to function and grow. DNA’s structure is now well-known. Most Americans are familiar with its double-helix shape. In 1953, however, that shape was unknown to the world. What Watson and Crick discovered was that it was ladder-like, with two strong, parallel bars made from a combination of sugar and phosphate molecules, joined weakly together by the linking of nitrogenous molecules jutting out from the sides. As the two scientists already knew, there are four kinds of nitrogenous base molecules that help join DNA’s two backbones: adenine, guanine, thymine, and cytosine. When their bonding is complete, the result looks like a ladder; thanks to the chemical properties of DNA’s constituent parts, that ladder takes the twisted shape known as the double helix.

Watson and Crick did not discover DNA’s structure all by themselves. In fact by the time they started working, in the middle of the twentieth century, there was much information about DNA already in circulation, and many rival camps of scientists were striving simultaneously to discover the rest. In 1944 the American scientist Oswald Avery made the stunning discovery that DNA was an acid—not, as previously believed, merely a special kind of protein. Experimenting with the bacterium pneumococcus, Avery found that by altering one of the sticky acids within the creature he could miraculously transform the pathogen into a far deadlier form. Clearly, he concluded, this mysterious acid had the capacity to dramatically influence the structure of the larger creature. In 1952 the collaborators Martha Chase and Alfred Hershey confirmed Avery’s results and triggered a fierce contest to become the first to reveal the one of the minutest, most basic, and yet most elusive secrets of life on earth.

After the Hershey-Chase experiments, the future Nobel laureate Linus Pauling, already a famous scientist, was the bettors’ favorite in the race to understand DNA. Nobody imagined the victory would go to the two young men at Cambridge. What Watson and Crick came to understand before their competitors, however—and Watson had his key insight on February 21—was that the four nitrogenous molecules that link together the two backbones of DNA always match up in the same pairs: adenine always couples with thymine, guanine with cytosine. These paired bases make chains of exactly the same length, enabling them to join with each other across the gap between DNA’s sugar-phosphate backbones. Furthermore, it is this reliable pairing system that makes it possible for DNA to replicate itself. When the cell reproduces DNA, the two backbones peel apart from each other; because each base has only one possible partner, each of the individual strands contains all the information necessary to rebuild the entire DNA molecule.

Watson and Crick were clever enough to uncover the secret of DNA, but they also concealed a few secrets of their own, chief among them what some have called one of the most serious cases of academic dishonesty in modern history. In the papers in which they publicized their discovery, they never cited the work of a much less well-known scientist, Rosalind Franklin. Franklin worked at a different laboratory but on a similar project. She took extensive x-ray photographs of microscopic molecules of DNA. Watson attended one of her lectures in November 1951, and there he learned enough information to put him and his partner well on their way to successful experimentation.

More important, on January 28, 1953, Watson attended a presentation at which Franklin described some of her unpublished work. After the presentation he was approached by Maurice Wilkins, a colleague with whom Franklin was feuding, and Wilkins surreptitiously showed him a particularly intriguing piece of Franklin’s experimental data, the so-called “Photograph 51.” Photograph 51 was a crucial piece of evidence that helped spark Watson and Crick’s final discovery. It showed the corkscrew-like shape of DNA’s interwoven strands, though neither Wilkins nor Franklin yet understood its significance. With Wilkins’s act of betrayal, Watson was suddenly able to complete the work that would make him and his collaborator famous—and that would win them, and Wilkins with them, a Nobel Prize.

Watson and Crick’s announced results of February 1953 changed the course of history. Here in the United States, the consequences of understanding the structure of DNA are most familiar in our own time through the Human Genome Project. Initiated in the autumn of 1990 by the National Institutes of Health and the Department of Energy, the Human Genome project successfully mapped, by the first years of the new millennium, each individual gene of the human genome. As a result we understand the workings of human life—and of other forms of life too—far better than ever before, and medical science promises to make ample and benevolent use of this information in the pioneering of new treatments and cures.

It is surely worth remembering the scientists we have long recognized for making such present-day achievements possible. But we also mustn’t forget those, like Rosalind Franklin, who made invaluable contributions to the progress of mankind while asking—and receiving—nothing in return.

—Alexander Burns, an undergraduate at Harvard College, is a frequent contributor to AmericanHeritage.com.