By Jean Balchin 28/06/2017


This grainy, black and white photograph is quite possibly the most important photograph in human history.

Photograph 51, the unimaginatively-named X-ray diffraction image of DNA was taken by Raymond Gosling in May 1952, a PhD student under the supervision of Rosalind Franklin at King’s College London. Photograph 51 triggered the development of the DNA model and confirmed the prior postulated double helical structure of DNA. The photograph also illustrates how petty feuding got in the way of scientific development.

I was actually introduced to the concept of DNA by another illustration; a deftly-drawn cartoon by the perennially hilarious Gary Larson. Two squat, rather dull-looking men sit guzzling beer at a pub, while an equally sluggish bartender turns to address another patron — a thickset young man crying “I’ll have a double, Felix!” As a child, I used to curl up for hours flicking through my father’s collection of The Far Side cartoons. I loved the hapless, bespectacled people of Larson’s imagination, and their preoccupation with roadkill, brussel sprouts and all things ridiculous. I didn’t grasp the implications of this particular cartoon however, until I was about 12 years old, and chanced upon an old biology textbook in my Dad’s study. The double helical structure of DNA amazed me. It was so eloquent, neatly coiled up within nearly every cell in my body. Watson and Crick became my teenage idols, alongside the likes of Christina Aguilera and James McAvoy. I didn’t know then that a kiwi scientist, Maurice Wilkins, had contributed to this discovery. I didn’t know that an English chemist called Rosalind Franklin was also involved.

DNA

DNA (deoxyribonucleic acid) is essentially the essence of life. It is the hereditary component in humans and most other organisms. Nearly every cell in the human body contains the same DNA, mainly in the cell nucleus. A small amount of DNA may also be located in the mitochondria. The information in DNA is encoded in the various sequences of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order of these bases determines the information available for building and maintaining an organism, and we humans possess about three billion bases. DNA bases pair up with each other to form units called base pairs. A pairs with T, and C with G. Each base is attached to a phosphate molecule and a sugar molecule.

The combination of a base, a sugar molecule and a phosphate molecule is called a nucleotide. These nucleotides are strung together in two long strands that spiral around each other in a double helix formation. If one were to take a hypothetical magnifying glass of extraordinary capacity and examine nuclear DNA, one might see something akin to a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder. DNA’s most important feature is that it can replicate itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is incredibly important, because when cells divide, each new cell must have an exact copy of the DNA present in the old cell.

Who was Maurice Wilkins?

Maurice H F Wilkins

Maurice Wilkins was born in the small town of Pongaroa, north Wairarapa in Aotearoa. Wilkins’ family was from Dublin, where his his paternal and maternal grandfathers were, respectively, Headmaster of Dublin High School and a Chief of Police. The young Maurice Wilkins was uprooted from New Zealand at the age of six when his family moved to Birmingham, England. Wilkins went to Cambridge University in 1935, where he studied physics. He went on to study his Ph.D. at the University of Birmingham, publishing three papers on phosphorescence and electron traps in 1945, in the Proceedings of the Royal Society. After earning his Ph.D., Wilkins contributed to WW2 by improving cathode-ray screens for radar and working on the Manhattan Project. Deeply regretting his role in developing the catastrophic atomic bomb, Wilkins turned his attention to science that was beneficial for humanity, joining the biophysics unit at King’s College, Cambridge, with his mentor, John T. Randall.

Wilkins began his work here by studying nucleic acids and proteins via X-ray imaging. He was very adept at isolating single fibres of DNA and had grasped a rudimentary understanding of nucleic acid structure when Rosalind Franklin, an English chemist and X-ray crystallographer joined the team. Upon being recruited, Franklin was told that she would be in charge of the X-ray studies of DNA. Wilkins however was under the impression that Franklin would be his assistant. To this end, chemistry sparked between the pair bad chemistry. Franklin was a blunt, outspoken woman whereas Wilkins was quiet, unobtrusive and non-confrontational. They clashed bitterly, and generally avoided each other in the lab. Sadly, had they cooperated better, Wilkins and Franklin might have been the first to discover DNA’s structure.

Photograph 51

As it happened however, James Watson was shown Photograph 51 by Wilkins without Franklin’s approval or knowledge. By this time however, Raymond Gosling, the photograph’s discoverer, had returned to the supervision of Wilkins. Along with Francis Crick, Watson studied the features of Photograph 51 to develop the chemical model of the DNA molecule. Photograph 51 was incredibly revelatory. The diffraction pattern determined the helical nature of the double helix strands, and calculations from the photograph provided crucial parameters for the size and structure of the helix. Growing evidence supplied by geneticists that it was DNA, rather than protein in chromosomes that was responsible for heredity, and Erin Chargaff’s experimental finding that there are equal numbers of A and T bases and of G and C bases in DNA spurred Watson and Crick on, as did Linus Pauling’s discovery that the molecules of some proteins have helical shapes.

Historians of science have argued for decades over the significance of this image to the work of Watson and Crick, as well as the methods by which they obtained the image. Should Wilkins have shown Photograph 51 to Watson and Crick without Franklin’s knowledge? Would Franklin have deduced the structure of DNA on her own, from her own data, had Watson and Crick not seen Photograph 51? Was Franklin unfairly treated in the lab? As it happened, Wilkins’ work was published as supporting data to the Watson-Crick model of DNA. He went on to devote much time and energy to proving the model correct, but it was Watson and Crick who became household names. Wilkins became the “third man of DNA”, to his chagrin. In 1994, he told the New Zealand Listener, “if you have something as explosive in its profound scientific effects as DNA, it is normal to get some very big tensions building up between the people involved”. Rosalind Franklin missed out on the 1962 Nobel Prize; she died of cancer in 1958 at the age of 37.

Regardless of the controversy, the discovery of DNA’s structure was stupendous, enabling scientists to explore the fundamental nature of human beings. We owe much to Maurice Wilkins and Rosalind Franklin, as well as James Watson and Francis Crick.

 

Featured image: Photograph 51, X-Ray Diffraction image, courtesy of Wikimedia Commons