| DNA (deoxyribonucleic acid) is a very long molecule that is densely packed and so ordinarily its molecular structure would be difficult to analyze using crystallography. However, it can be prepared for X-ray crystallography by extracting it from cells in gel form and then slowly drawing it into fibers in which the molecules run parallel. This regular arrangement of molecules can then be analyzed by X-ray diffraction. Initial analysis by W. T. Astbury indicated that the DNA bases were stacked on top of each other "like a pile of pennies." Later work with clearer images by Wilkins, Franklin, and colleagues revealed the double helix structure, furthered by Crick and Watson's realization that the bases were paired but ran in opposite directions. |
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