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
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
scientific researchers of the twentieth century But in the early 1950s she had to follow where opportunities led The grants and stipends that supported her work came from institutions that were pursuing scientific problems of their own and these did not necessarily match her interests As an independent woman who needed to support herself she had to consider carefully any opportunities that came her way She still was not sure about the significance of Photograph 51 In her view the molecule’s structure needed to be worked out precisely using careful mathematical calculations and relying on evidence and proven facts A simple photograph a theory or even a three-dimensional model simply was not enough DNA the chemical code of life was too important to be solved with such pictures and toys It had to be solved the right way the scientific way 10 Photograph 51
