Who was Rosalind Franklin?
Rosalind Franklin - British biophysicist and X-ray crystallographer
Rosalind Franklin was a pioneering British biophysicist and X-ray crystallographer born on July 25, 1920, in London. She played a crucial role in understanding the molecular structures of DNA, RNA, viruses, coal, and graphite. Excelling in science from a young age, she earned her Ph.D. from the University of Cambridge. Franklin is best known for her pivotal contributions to the discovery of DNA's double helix structure during her tenure at King's College London in the early 1950s. Her meticulous X-ray diffraction work led to the capture of Photograph 51, an image that provided critical evidence of DNA's helical structure.
What is Photograph 51?
Photograph 51 taken by Rosalind Franklin and Raymond Gosling in May 1952
Photograph 51 is an X-ray diffraction image taken by Franklin and her research student, Raymond Gosling, in May 1952. This image revealed key details about the helical nature of DNA, showing a backbone of alternating deoxyribose and phosphate moieties, with the base pairs inside the helix. This photograph provided essential parameters for the size and structure of the helix, aiding James Watson and Francis Crick in developing the first accurate model of DNA's double helix structure. Their findings were published in 1953, garnering widespread recognition.
Franklin's Legacy
Despite the substantial impact of her research, Franklin's work was not recognised during her lifetime. In 1958 she died aged 37. The scientific community later acknowledged her critical role in the discovery of DNA's structure. Today, Rosalind Franklin is celebrated as a key figure in molecular biology, whose pioneering efforts laid the groundwork for significant advancements in genetics and biochemistry.
The Story Behind the Discovery
In 1951, Franklin joined Kings College to study DNA structures using X-ray diffraction and worked with John Randall and Maurice Wilkins. Photograph 51, a clear image taken by Franklin and Gosling, demonstrated DNA's helical structure and was shown to James Watson by Maurice Wilkins. This enabled Watson and Crick to build the first model of the molecule, leading to their discovery of the three-dimensional double helix structure of DNA.
Nobel Prizes are not awarded posthumously and although Watson, Crick, and Wilkins received the Nobel Prize in Physiology or Medicine in 1962, Franklin's contributions were not recognized by this award. She is often portrayed as a victim who was unable to decipher what her own data revealed about DNA, and that only Watson was able to understand the significance of Photo 51 at a glance. However, recent research by Matthew Cobb and Nathaniel Comfort suggests Franklin was an equal player in this scientific discovery. Their findings, published in a 2023 article in Nature1, reveal that Franklin's role was pivotal and collaborative.
At King’s College London, biophysicists funded by the Medical Research Council (MRC), led by John Randall and Maurice Wilkins, used X-ray diffraction to study the DNA molecule. Franklin’s careful preparation of DNA fibres and her X-ray diffraction expertise led to the iconic Photograph 51, which displayed the characteristic cross pattern of diffraction spots indicating a helical structure.
Image courtesy of Brian Sutton, Professor of Molecular Biophysics at Kings College in ‘The Story behind Photo 51’. “If a helix is viewed in this way from the side, then it has a repeating “zig-zag” appearance, which will give rise to a series of diffraction spots at right angles to the regular arrays of the zigs and the zags, forming a characteristic “cross” pattern, so clearly seen in Photograph 51.”.2
Understanding X-ray Diffraction
X-ray diffraction (XRD) is a non-destructive laboratory technique that measures the scattering of X-rays produced by the atoms of a crystal. This technique provides information about the structure of a crystal, such as chemical composition, orientation, size, and layer thickness. In Franklin's case, X-ray diffraction was crucial in revealing the repeating helical structure of DNA.
Franklin used X-ray film to acquire XRD images using a laboratory X-ray source. Technology has advanced since the 1950s and XRD is undertaken using powerful synchrotron light sources as well as sophisticated laboratory X-ray sources. Digital X-ray detectors have replaced film, first using CCD image sensors and more recently CMOS images sensors and direct conversion detectors. Spectrum Logic manufactures several X-ray detectors that can be used for XRD with synchrotron light sources as well as laboratory X-ray sources. For example, the 2824HR with 50 µm pixel and 27 MP resolution and is now available in a water-cooled version to reduce dark noise and allow longer integration times. The 1412HS with 100 µm pixel and 1.7 MP resolution offers 110 fps in full resolution with higher frame rates possible in region of interest modes.
Conclusion
Rosalind Franklin’s work, particularly Photograph 51, was essential in uncovering the structure of DNA, cementing her legacy as a pioneering scientist whose contributions significantly advanced our understanding of molecular biology.
2. ‘The story behind Photograph 5’ Brian Sutton, Professor of Molecular Biophysics. 14/04/2023