Rosalind Franklin: DNA Discoverer

Rosalind Franklin: DNA Discoverer — page 3 — and the math they had to use was complex Yet the work was leading them on a trail of discovery into the fundamental secrets of life Women in Chemistry Women have made important contributions to chemistry since the science began In the late eighteenth century Marie Lavoisier worked as a laboratory assistant to her husband Antoine-Laurent helping him develop a new scientific method for understanding the elements She translated scientific articles from English to French and created beautifully precise drawings of laboratory experiments and equipment Born in Poland Marie Curie worked as a researcher in physics and chemistry in France With her husband Pierre Curie discovered the elements polonium and radium Their studies of radioactivity earned the two a share of the 1903 Nobel Prize in physics After Pierre’s death Marie helped develop the medical use of X rays and won the 1911 Nobel Prize in chemistry making her the first person ever to earn two Nobel Prizes Dorothy Hodgkin like Rosalind Franklin was a skilled X-ray crystallographer Using this method she discovered the structure of penicillin insulin and vitamin B12 She won a Nobel Prize for her work in chemistry in 1964 THE DOUBLE HELIX Franklin and Gosling were creating X-ray images of thin delicate fiber-like structures By measuring the details on the image they could figure out how chemical compounds and molecules invisible even to microscopes made up the structures One image taken by Gosling showed two strands crossing each other in the shape of an X The strands appeared as a series of steps like the rungs of two ladders crossing in the center Franklin and Gosling were not sure what to make of the image but the shape of the strands was clear they 6

Rosalind Franklin: DNA Discoverer — page 4 — showed the structure of a double helix The image was much sharper than many others the scientists had taken in the lab It became known as Photograph 51 Franklin was secretive about her work as were other scientists working in the lab They wanted the opportunity to announce discoveries as their own Instead of showing the image to her colleagues she kept it with other images in her office When she was ready with her calculations and findings she would write everything in a paper She would share the paper with a few other scientists at King’s College Then she would announce her findings at a lecture or seminar She would seek input from her scientific peers and then prepare an article for publication in a journal This would allow her to claim a discovery if in fact the photograph showed anything significant Gosling and Franklin were also competing with other scientists in England and in the United States In fact James Watson and Francis Crick members of the prestigious Cavendish Laboratory at Cambridge University were working on the same problem the structure of deoxyribonucleic acid or DNA for short the molecule that passes genetic information from parents to offspring Linus Pauling a molecular chemist at the California Institute of Technology was publishing articles on this very subject and he was drawing near to a solution 7

Rosalind Franklin: DNA Discoverer — page 5 — Secrets of Photograph 51 For such an important image in the history of science Photograph 51 does not look like much only a blurry image of two broken lines crossing at the center to form an X But the image shows several important facts The X pattern is created by a helical molecule which appears in the image as two branches crossing at perpendicular angles Four white diamond shapes at top bottom left and right indicate the helix pattern continues repeating itself beyond the image boundaries In addition the top and bottom diamonds are slightly lighter which means the backbones of the molecule lie on the outside of the molecule and the chemical bases on the inside that every scientist in the same field knew would bring honors and fame It was not only the math the use of complicated equipment and the competition that were challenging Franklin Every other researcher at King’s College and nearly all of the scientists at the Cavendish Laboratory were men Although they respected her ability they did not completely accept her as a colleague She did not take part in the casual friendly conversations in which ideas could be traded and solutions challenged She could not eat at the exclusively male college dining halls or relax at the men-only British pubs Nevertheless Franklin was closing in on a solution to one of the most important scientific mysteries how an organism passes its structure and characteristics to the next generation Although her training was in chemistry this work was bringing her into new realms of genetics and molecular biology Her discoveries would eventually bring her renown as one of the most talented 8

Rosalind Franklin: DNA Discoverer — page 6 — SCIENCE SPOTLIGHT THE DISCOVERY OF DNA In 1869 young German researcher Johann Friedrich Miescher made an interesting discovery Miescher wanted to study what was inside a single cell First he collected pus from a hospital’s used bandages He created tiny samples to look at the cells that made up the pus Through a series of experiments Miescher managed to extract a new chemical from the cells Because this material came from the cell nucleus he called it nuclein Hydrogen oxygen nitrogen and phosphorous atoms were present in nuclein which made it a relatively simple molecule In Miescher’s time there were many theories afloat on the mechanism of heredity How do parents pass on their characteristics to offspring Why do people have blue brown and hazel eyes for example and how does this single trait one among many come about in a newborn The botanist Gregor Mendel in his study of pea plants concluded that both parents pass on a set of instructions to their offspring and that certain traits are dominant more likely to appear in a younger generation But the mechanism of passing on the genetic map was still unknown Miescher and other scientists realized that some component of the human cell must be responsible But in Miescher’s view nuclein’s simple chemistry disqualified it from having anything to do with the complex way humans inherit characteristics from their parents Eventually in the 1930s nuclein would gain a new more precise name deoxyribonucleic acid or DNA 9

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