Rosalind Franklin and DNA.Rosalind Franklin (above right) took the diffraction photograph that led to Watson and Crick’s publication of the helical structure of the B form of DNA. A reconstructed

precession image. Each point of light is interpreted as a

‘reflection’ from a plane of atoms. Thousands of these

reflections are collected and how bright they are and the

angle at which they are collected is used to determine

the position of the atoms in the crystal. Reflections further away from the centre (at

higher angle) are used for high-resolution data.

X-RAY CRYSTALLOGRAPHY

X-ray Generators - Different Scales.X-rays can be generated in the laboratory (above right) from the domestic power supply - or, very powerful X-rays of tuneable wavelength, can be generated at synchrotron facilities like the Diamond Light Source in Harwell, Oxfordshire (above left).

Watson and Crick and their model of DNA (above) based on Rosalind Franklin and Maurice Wilkins’ diffraction photographs.

Dorothy Hodgkin and Insulin.

She worked for over 30 years to fully calculate the structure of insulin (behind) at a time when all the diffraction intensities had to be

determined by hand.

References and CitationsStructures downloaded from the RSCP Protein Databank. (http://www.rcsb.org/pdb/home/home.do) (from top: b-DNA, hen’s egg lysozyme, HIV reverse transcriptase, pig insulin).b-DNA, lysozyme and reverse transcriptase rendered using Qutemol (M Tarini, P Cignoni, C Montani, IEEE Transactions on Visualization and Computer Graphics, 12 , 5, 1237-1244 , 2006.) Pig insulin rendered using PyMol (The PyMOL Molecular Graphics System, Version 1.5.0.4 Schrödinger, LLC.) Portrait photographs copyright of Sciencephotolibrary and Life Science Foundation (http://www.lifesciencesfoundation.org). All used without permission. Bruker Microstar photograph copyright Mairi Haddow, University of Bristol. Photograph of Diamond Light Source copyright of that organisation.

JD Bernal and Kathleen Lonsdale. Lonsdale confirmed the structure of benzene using X-ray diffraction. Bernal, among other things, worked on Tobacco Mosaic Virus.

Father and son, the Braggs, worked together to develop Bragg’s Law - the fundamental equation in X-ray crystallography.

X-rays were discovered in 1895 and are part of the electromagnetic spectrum - like visible light. Like all light they have a wavelength and frequency. Their wavelength is about the same distance as the space between atoms in solids. When X-rays pass through a crystal - the X-rays form a diffraction pattern. Analysing the diffraction pattern using computers allows us to reconstruct the 3D structure of the crystal. Knowing the structure of molecules is vital to our understanding of structure and function and has revolutionised fields as diverse as medicine and electronics. Crystals of lysozyme.

The first enzyme to have its structure determined. Lysozyme crystals show beautiful

symmetry. Lysozyme is important in our defence against bacteria.

The structure of HIV reverse transcriptase. This is used to convert RNA into DNA within infected cells. Understanding its structure allows scientists to develop drugs to treat disease.