Techniques : X-ray Crystallography

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X-ray Crystallography

Timeline: 1953

Scientist Profiles
Franics Crick
James Watson

Web Link:
Complete Text: Original Paper on the Structure of DNA

The technique first developed by Maurice Wilkins and Rosalin Franklin and used by James Watson and Franics Crick to determine the double helix structure of DNA is known as X-ray crystallography. X-rays are synchronized so that the crests and troughs are in identical locations. These rays are then bounced off of the DNA molecule to form an image on photographic film. X-rays are used due to their low wavelength, between 0.05 angstrom and several hundred angstroms. The wavelength of normal light is hundreds of times longer, making the offset caused by the molecule so small that it is of no use. As the X-rays impact the DNA, they are reflected at different angles and at different times in their cycles (because the distance traveled is different for each wave). This causes a pattern to form. However, when only one molecule is used, the image is very faint. To enhance and amplify it the image, the molecules must be arranged in order, as in a crystal. DNA is arranged in crystal form by turning it into a gel. A small object can then be inserted into X-ray image

the mixture. When twisted, the object will pull out a strand of several DNA molecules, all in order. This strand can then undergo X-ray crystallography, and produce a much stronger image.

X-ray crystallography image courtesy of the British Biophysical Society.

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