How did the work of other scientists help Crick and Watson to develop their theory for the structure of DNA?

● Maurice Wilkins biography (whatisbiotechnology.org/index.php/people/sum mary/Wilkins) ● Erwin Chargaff, Discovering the rules of complementary base pairing (dnalc.cshl.edu/view/15251-Discovering-the-rulesof-complementary-base-pairing-Erwin-Chargaff.h tml) ● National Medal of Science, Erwin Chargaff (nationalmedals.org/laureate/erwin-chargaff/) ● Doug Stewart, "Erwin Chargaff", Famous Scientists 9 August 2016 (famousscientists.org/erwin-chargaff/) ● Kara Rogers, ‘Friedrich Miescher, The

Encyclopaedia Britannica, 22 August 2021 (britannica.com/biography/Friedrich-Miescher) ● ‘Friedrich Miescher’, DNA From the Beginning (dnaftb.org/15/bio.html) ● Erik Gregersen, ‘Phoebus Levene’, The

Encyclopaedia Britannica, 2 September 2021 (britannica.com/biography/Phoebus-Levene)

Footnotes

[1] ‘The Discovery of DNA’s Structure’ (pbs.org/wgbh/evolution/library/06/3/l_063_01.html) [2] See the end of the paper for picture of ‘Exposure 51’ [3] James Watson and Francis Crick, ‘Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid’, Nature, 25 April 1953 [4] Erwin Chargaff, ‘Heraclitean Fire’, 1 June 1978 [5] Awards Erwin Chargaff received included: Pasteur Medal in 1949, Carl Neuberg Medal in 1958, Charles Leopold Mayer Prize in 1963, Heineken Prize in 1964, Gregor Mendel Medal in 1974, and the National Medal of Science in 1975

Take 2. How did the work of other scientists help Crick and Watson to develop their theory for the structure of DNA?

By Sia Patel Year 12 James Watson and Francis Crick reached a groundbreaking conclusion in 1953[1] , when they discovered that the DNA (deoxyribonucleic acid) molecule, which contains the hereditary information of cells, is in the shape of a three-dimensional double helix. However, they were not the only people who had been working on this theory at the time, and were heavily influenced by other scientists of their era. Without these other scientists’ research, it is highly unlikely that Crick and Watson would have developed their pioneering hypothesis. One of the most influential scientists on Crick and Watson’s theory was English chemist Rosalind Franklin. After completing extensive research on the chemistry of carbon and coal, which allowed great strides to be made in the war effort, Franklin joined the Biophysical Laboratory of King's College, London as a research fellow in 1951. Whilst at the College, she completed extensive X-ray diffraction work on DNA. This led to her discovering first the density of DNA as well as the fact that it could exist in 2 forms. Franklin and PhD student Raymond Gosling (1953)[2] subsequently captured one of the most significant photographs of all time: an image of one of the forms of DNA that revealed its double helical

structure, known as Photo 51 (left). Franklin (1953)[2] states that, according to her research, it is highly probable that the structure of DNA is helical. Franklin’s image helped to confirm Crick and Watson’s hypothesis that DNA exists in a double helical structure, allowing them to continue their work and eventually build their model and making Franklin one of the most influential scientists on the double helical theory. Another scientist who greatly aided Crick and Watson in their work was New Zealand-born British biophysicist Maurice Wilkins. Following World War II, Wilkins joined King’s College London as Assistant Director of a new biophysics unit. It was then that he and Ray Gosling began to use X-ray diffraction to obtain images of different forms of DNA, a technique that Rosalind Franklin later built upon to take Photo 51. Wilkins and his team (1953)[3] spent years confirming the accuracy of the Watson-Crick (1953)[1] proposal, and in 1962 he received the Nobel Prize in Physiology or Medicine alongside Watson and Crick. Franklin, who had passed away due to ovarian cancer four years earlier, was not included in this. Another way in which Wilkins contributed greatly to Crick and Watson’s research was by showing the pair Franklin’s (1953)[2] Photo 51. This was integral to the development of their theory, although Franklin was not informed of this and did not gain credit when their findings were published. Overall, Wilkins had a profound impact on Crick and Watson’s theory by both confirming its accuracy and by revealing the significant Photo 51 to them, clarifying their theory further. Although Crick and Watson worked directly with Franklin and Wilkins to advance their theory, they may not have reached this conclusion to begin with without the momentous discoveries of past scientists. One notable example is Russian-born American biochemist Phoebus Levene. After emigrating to the US at the age of 22, Levene was appointed to the Rockefeller Institute for Medical Research, where he remained for the duration of his career. Although it was known that nucleic acids existed in two forms, and that they contained the bases Adenine, Guanine, Cytosine and Thymine/Uracil, virtually nothing was known about the structure or function of nucleic acids. It was also found that one of the two types of nucleic acid was found in the thymus of animals and that the other was found in yeast. Levene (1908)[4] made the discovery that the pentose sugar ribose is found in yeast nucleic acid, and subsequently established the tetranucleotide hypothesis. This hypothesis suggested that the four bases were present in approximately equal ratios in nucleic acids. Levene, along with L.A Mikeska and T. Mori (1929)[5] , states that deoxyribose is the carbohydrate found in animal thymus nucleic acids. Levene continued to work on his model for the structure of nucleic acids until 1935[6] , when he published a paper stating his improved model, in which the links of the phosphates

between the deoxyriboses are correct. Although Levene’s model of RNA contained some errors, his groundbreaking work allowed scientists of Crick and Watson’s time to further their conclusions as they knew the basic structure of nucleic acids and could focus on developing the existing models. Another scientist who laid the foundation for Crick and Watson’s discoveries was Austro-Hungarian-born biochemist Erwin Chargaff. At the time of Chargaff’s research, it was widely accepted that the carriers of genetic information were the amino acids, which could combine in numerous ways to form a complex basis for genes. However, Chargaff’s research suggested that it was instead the DNA that carried genetic material, due to the fact that differences between the DNA of different species were discovered. Chargaff then performed experiments on DNA involving the separation of the purines and pyrimidines using paper chromatography. By doing this, he discovered that adenine and thymine exist in roughly equal proportions in the DNA of all species, as do guanine and cytosine. However, he also discovered that the amount of the purines and pyrimidines varied across different species, giving the reason for genetic variation within species. Chargaff’s work directly led Crick and Watson to determine their theory, as the two scientists reached the conclusion that, because adenine and thymine are always present in equal proportions, they must always bond together, and the same for guanine and cytosine. This further allowed Crick and Watson to develop their model with the pyrimidine and purine bases bonding the two strands of DNA together. In conclusion, the cumulation of decades of research done by other scientists allowed James Watson and Francis Crick to develop their theory that the DNA molecule has a double helical structure. Rosalind Franklin and Maurice Wilkins confirmed the accuracy of the theory, whilst Phoebus Levene and Erwin Chargaff laid the foundation for the theory with their extensive research on components of the structure of DNA.

References

[1] Watson, J.D and Crick, F.H.C (1953) Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid. Nature. 171, 737-738 [2] Franklin, R.E and Gosling, R.E (1953) Molecular Configuration in Sodium Thymonucleate. Nature. 171, 740-741 [3] Wilkins, M.H.F, Stokes, A.R and Wilson, H.R (1953) Molecular Structure of Deoxypentose Nucleic Acids. Nature. 171, 738-740 [4] Mandel, J.A, Jacobs, W.A and Levene, P.A (1908) On Nucleic Acids. Journal of Biological Chemistry. 4, 92-94 [5] Levene, P.A, Mikeska, L.A and Mori, T (1929) On the Carbohydrate of Thymonucleic Acid. Journal of BiologicalChemistry. 785-787 [6] Levene, P.A and Tipson, R.S (1935) The Ring Structure of Thymidine. Journal of Biological Chemistry. 110, 623-630 All of these are scientific papers written in collaboration with other scientists. Scientific papers are also peer reviewed and so have a high reliability.

They are also primary sources, written by the scientists themselves, and so are very reliable sources to use in my research.

Sources

● Nature Education (2008) Discovery of DNA

Structure and Function: Watson and Crick.

Available from:nature.com/scitable/topicpage/discovery-ofdna-structure-and-function-watson-397/ [Accessed 09/10/21] ● U.S National Library of Medicine. The Discovery of the Double Helix, 1951-1953. Available from: profiles.nlm.nih.gov/spotlight/sc/feature/doublehe lix [Accessed 08/10/21]

This is a reliable source as all content in the U.S National Library of Medicine is peer-reviewed and the webpage contains a vast array of scientific publications]

This is a reliable source as Nature is a world-renowned scientific journal,inwhichmany of the scientific papers mentioned in the essay

Recen Scientifi Activit

We spoke to students throughout the school to see what Science Faculty activities they’ve been involved in this academic year…