Double Helix: How an Image Sparked the Discovery of the Secret of Life
structure of the DNA molecule would help answer a great mystery of life How do organisms live grow develop and survive generation after generation Watson thought the answer might lie in DNA Questions about the mysterious molecule had brought him across the Atlantic Ocean to labs in Europe three years earlier It was well known that DNA was composed of a few basic parts phosphate and sugar molecules that were linked to form chains Scientists also knew that DNA contained four types of nitrogen-based molecules called bases adenine cytosine guanine and thymine But how did these simple building blocks all fit together King George IV and the Duke of Wellington founded King’s College London in 1829 It is part of the University of London Watson burst into King’s physics labs eager to share a new scientific paper written by Linus Pauling of the California Institute of Technology It described how these simple parts could build a DNA molecule Twenty-four-year old Watson admired Pauling the 51-year-old chemist who had discovered that protein molecules could take the shape of a coil called an alpha helix In a 1950 lecture Pauling had presented his model of the single staircase-like structure and received worldwide praise There was
no one like Linus in all the world Watson once wrote The combination of his prodigious mind and infectious grin was unbeatable 2 Linus Pauling would win two Nobel prizes one in chemistry and one for his work for peace But the famed chemist had blundered with DNA and Watson knew it Pauling’s mistake was contained in a diagram in the paper Watson clutched Pauling imagined a triple helix of phosphate and sugar chains twisting around each other with the nitrogen bases attached and pointing outward like leaves on a tree branch Watson knew this theory was wrong because he had made an inaccurate triple helix model himself a year earlier On his way to find Wilkins Watson stopped by the office of another scientist Rosalind Franklin X-ray photographs and books were spread across her desk She was also deep into studying DNA’s structure but she was not interested in Pauling’s diagram She distrusted the celebrated scientist’s method He had discovered the alpha
helix structure in just a few hours by drawing on paper while sick in bed Franklin believed sketches or models could only come after meticulously collecting data She took careful measurements and made calculations based on her X-ray photographs of the DNA molecule Numbers and notes filled her notebooks not drawings Wilkins welcomed his friend Watson into his office He was glad for an opportunity to grumble about Franklin Though Wilkins and Franklin both studied DNA they competed rather than worked together The lab’s director John Randall had even given them separate workspaces and divided the DNA research so they could work independently Franklin enjoyed working alone but she also found King’s College old fashioned and unwelcoming Scientists gathered in a men-only commons room for lunch and discussion She wrote to a friend in Paris that at King’s there was nobody with whom I particularly want to discuss anything scientific or otherwise 3 Women including scientist Rosalind Franklin were not always welcomed to the male-dominated collegiate world Franklin refused to discuss anything scientific with Watson during his trip to the King’s labs Yet without knowing it she would help him and his Cambridge colleague Francis Crick make history Out of a drawer in his office Wilkins pulled an X-ray photograph made in the lab by Franklin and her assistant Raymond Gosling She had labeled it Photo 51 Without asking her permission and in a move that many scientists have said is unethical Wilkins showed it to Watson
Linus Pauling received a copy of Photo 51 taken by Rosalind Franklin The name of her graduate assistant Raymond Gosling also appears on the note To the untrained eye the photograph was simply a grainy black and white image of dark marks scattered in roughly the shape of an X But to someone skilled in crystallography the science of determining the arrangement of atoms in crystals it was a clear portrait of a DNA fiber taken with X-rays John Bernal an early developer of the X-ray photography technique praised Franklin for the extreme clarity and perfection in everything she undertook Her photographs are among the most beautiful X-ray photographs of any substance ever taken 4 Wilkins knew the importance of Franklin’s Photo 51 The X shape confirmed his guess of DNA’s structure I had this photograph and there was a helix right on the picture You couldn’t miss it 5 he later said Watson saw it too The instant I saw the picture my mouth fell open and my pulse started to race 6 he remembered While riding the train back to Cambridge Watson drew what he remembered of Photo 51 in the margin of a newspaper Helices curved around each other like spiral staircases He did not want to forget what he had seen before he could share it with his lab mate Francis Crick Unlike Wilkins and Franklin he and Crick were friendly and
