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X-Ray specs

Updated Thursday, 3rd August 2006

The role of X-Ray crystallography in the discovery of DNA.

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Nicholas Fry as Raymond Gosling, who pioneered techniques in X-ray diffraction photography Copyrighted  image Icon Copyright: BBC
Nicholas Fry as Raymond Gosling,
who pioneered techniques in X-ray
diffraction photography

X-Ray crystallography has become a vital technique in modern science and perhaps the most famous discovery brought about using the technique is that of the structure of the DNA molecule, the carrier of hereditary information.

When X Rays pass through a crystal they are diffracted or scattered by the regular arrangement of atoms within the crystal. The patterns of interference that result from this can be photographed and analysed to reveal the atomic structure. Although the discovery of the structure of DNA is credited to Francis Crick and James Watson, vital ground work was carried out by the British biophysicist Rosalind Franklin and Raymond Gosling.

Franklin carried out X-ray diffraction studies on the structure of the DNA molecule while working in the laboratory of the biophysicist Maurice Wilkins. The patterns that Franklin identified gave Crick and Watson the vital clue to determining the helical structure of the molecule,which they published in the journal 'Nature' in 1952. Crick, Watson and Wilkins would share the Nobel Prize for their efforts in 1962.

DNA is the substance that transmits genetic information from one generation to the next, but until Crick and Watson's work the structure of the molecule was a mystery. Without this understanding it was unclear how the DNA molecule was copied from cell to cell. Once it was understood to have a double helical structure, the mechanism of inheritance began to become clear.

Crick and Watson's great breakthrough was to realise that the molecule was made up of two long strands in the form of a double helix, rather like a long spiral ladder. The strands are made up of alternating phosphate and sugar molecules, with the nitrogen bases acting as rungs where they join in pairs. Each base is linked to a complementary base on the other side, and only particular pairings are possible: adenine with thymine, guanine with cytosine.

To make a new and identical copy of itself the DNA unwinds and each strand forms a template for two new double helices. In this way identical copies are made, allowing genetic information to be passed on from cell to cell and ultimately from generation to generation.

This DNA directs the formation of proteins, which are compounds central to all the processes of life. X Ray crystallography also led to an understanding of the structures of many of these enormously complex protein molecules, like Haemaglobin or Pennicilin. A knowledge of their structure has led to great breakthroughs in medicine and biology, and to our understanding of life itself.

 

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