Crick, Watson & Franklin

READING 5.4.2 CRICK, WATSON & FRANKLIN THEORIES OF EVOLUTION & LIFE Macquarie University Big History School: Core

Lexile® measure: 1100L MACQUARIE UNIVERSITY BIG HISTORY SCHOOL: CORE - READING 5.4.2. THEORIES OF EVOLUTION & LIFE: CRICK, WATSON & FRANKLIN - 1100L 2

DNA was discovered in 1869 by the Swiss doctor, Friedrich Miescher. He placed human eukaryotic cells under a microscope. Miescher saw DNA in the nucleus of the cells. CRICK, WATSON & FRANKLIN THEORIES OF EVOLUTION & LIFE By David Baker

Fifteen years later, German scientist Albrecht Kossel discovered what made this nucleic acid. It was made out of the organic chemicals adenine, thymine, guanine, cytosine and uracil. In 1889, German Pathologist Richard Altmann created the term “nucleic acid.” This is the “N” and “A” in deoxyribonucleic acid (DNA). In 1919 American scientist Phoebus Levene figured out that phosphorus held these chemicals together. In 1943, biochemists Oswald Avery, Colin McLeod and Maclyn McCarty made a very important discovery. They found out that DNA is what programs the individual traits of an organism. At last, the mechanism that had alluded Darwin as to how exactly traits were transmitted from parents to offspring in evolution was being made clear. The question was: just how did DNA work? By the 1950s, the great task for biochemists was to create a fully functional model of this highly complex structure. Francis Crick and James Watson began working on their model at Cambridge in 1951. They built prototypes out of steel or paper. Meanwhile at King’s College London, Maurice Wilkins, Rosalind Franklin, and her PhD student Raymond Gosling were working on X-ray diffractions to get a better idea of the shape and structure of DNA. The latter group relied heavily on finding solid proof for which model of DNA was the best fit. Francis Crick and James Watson’s work tended to be more theoretical. They were trying to come up with a model that functioned the best. MACQUARIE UNIVERSITY BIG HISTORY SCHOOL: CORE - READING 5.4.2. THEORIES OF EVOLUTION & LIFE: CRICK, WATSON & FRANKLIN - 1100L 3

Francis Crick and James Watson spent the next year and a half coming up with a thorough but flawed set of models of DNA. Working with blurry X-ray photos taken by William Astbury in the 1930s, along with a few slightly better photos, they eventually they tried the double-helix model. But even this had flaws. By 1953, Francis Crick and James Watson had been working on their model for nearly 2 years. They realized that they might be outdone by American biochemist Linus Pauling. He had recently put out his own flawed version of DNA’s structure. So Watson went on a trip to King’s College London to convince Wilkins, Franklin, and Gosling that they should join forces to beat Pauling to the punch. During Watson’s visit, Maurice Wilkins showed Watson “Photo 51” without asking his colleagues for permission. This was an X-ray diffraction of DNA that showed the structure more clearly. It was taken by student Raymond Gosling under the direction of his PhD supervisor Rosalind Franklin. Rosalind also provided much direct input on Crick and Watson’s model. She personally told them that their idea of putting the phosphate backbone on the inside was incorrect. Gosling and Franklin’s “Photo 51” was of such high quality that it enabled Crick and Watson to modify the model they had been working on since 1951. The research culminated in an April 1953 issue of the science journal did Raymond Gosling, Alex Stokes, and Robert Wilson, who were still Nature. This is where Watson and Crick published their model for DNA, alive and had also made contributions to the 1953 papers on the subject. alongside other papers published by the King’s College team. This included And so around the same period of time in the mid-20th century, three papers by Franklin and Gosling, and also by Wilkins, Stokes, and Wilson. breakthroughs had revolutionized science. The discovery of Cosmic Originally, Crick and Watson invited Maurice Wilkins to co-author their Background Radiation gave us the Big Bang. The vindication of Alfred DNA paper, but he refused. Nevertheless Crick and Watson’s paper made Wegener’s theory gave us plate tectonics. And the development of an direct reference to Wilkins’ and Franklin and Gosling’s papers citing the accurate model of DNA gave us a microscopic look at the origin of species. contribution of their work to the theoretical model. All these breakthroughs painted a picture of an ever-changing Universe, This was only the beginning, however. Crick and Watson continued to rather than one that is static and eternal, where species are immutable. It fine tune and improve their model of DNA over the next several years. It was breakthroughs like these that make narratives like Big History today was Francis Crick who first made a splash in the public during his pivotal possible. And it is breakthroughs like these that continue to update and lecture on the central principles of DNA replication in 1957. But at this improve that narrative with every year that passes. point, Crick and Watson’s model simply remained theoretical. It needed further evidence to back it up. There were still other contending models at play. Meanwhile in the same year, Rosalind Franklin passed away from cancer, possibly brought on by her exposure to X-ray radiation. Ultimately, the work of the Cambridge and King’s College teams culminated in the 1962 Nobel Prize for Physiology or Medicine. It was awarded to Francis Crick, James Watson, and Maurice Wilkins. Nobel prizes are not given posthumously, so Rosalind Franklin did not share in the prize. Nor MACQUARIE UNIVERSITY BIG HISTORY SCHOOL: CORE - READING 5.4.2. THEORIES OF EVOLUTION & LIFE: CRICK, WATSON & FRANKLIN - 1100L 4

REFERENCES Christian, David. Maps of Time: An Introduction to Big History. Berkeley: University of California Press, 2004. Christian, David and Cynthia Stokes Brown and Craig Benjamin. Big History: Between Nothing and Everything. New York: McGraw Hill, 2014. Gosling, Raymond (interview). “Due Credit” Nature vol. 496 (2013) Available from https:// www.nature.com/news/due-credit-1.12806 Maddox, Brenda. “The Double Helix and the ‘Wronged Heroine’” Nature vol. 421 (2003) pg. 407-408. Sayre, A. Rosalind Franklin and DNA. New York: W.W. Norton, 1975. Watson, James. The Double Helix: A Personal Account of the Discovery of the Structure of DNA. London: Atheneum Press, 1968. Wilkins, Maurice. The Third Man of the Double Helix: An Autobiography. Oxford: Oxford University Press, 2005.

IMAGE CREDITS ‘CRISPR Cas9’ Credit: National Human Genome Research Institute, https://www.flickr.com/ photos/genomegov/39603195652/ Creative Commons BY-NC 2.0 (https://creativecommons. org/licenses/by-nc/2.0/). ‘DNA sequencing. This method of DNA sequencing is called di-deoxy sequencing. It is used to determine the order of bases (A,C,G and T) in a piece of DNA using radioactively-labelled modified nucleotides. They are then separated by electrophoresis in a polyacrylamide gel and detected on x-ray film by a process called autoradiography.’ Credit: Michele Studer/ Wellcome Collection, https://wellcomecollection.org/works/c7sv89k4 Creative Commons BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ‘DNA probe for Y chromosome, meta/interphase’ Credit: Dr Rosemary Ekong/UCL/Wellcome Collection, https://wellcomecollection.org/works/zkmehrvs Creative Commons BY 4.0 (https://wellcomecollection.org/works/zkmehrvs?query=dna&page=1).

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