Watson, James Dewey  ( born April 6, 1928 , Chicago, Ill.,
U.S.American geneticist and biophysicist who played a crucial
role in the discovery of the molecular structure of
deoxyribonucleic acid (DNA), the substance that is the basis of
heredity. For this accomplishment he was awarded the 1962 Nobel
Prize for Physiology or Medicine with Francis Crick and Maurice
Wilkins.   After working at the University of Copenhagen, where
he first determined to investigate DNA, he did research at the
Cavendish Laboratories (1951–53). There Watson learned X-ray
diffraction techniques and worked with Crick on the problem of
DNA structure. In 1952 he determined the structure of the
protein coat surrounding the tobacco mosaic virus but made no
dramatic progress with DNA. Suddenly, in the spring of 1953,
Watson saw that the essential DNA components—four organic
bases—must be linked in definite pairs. This discovery was the
key factor that enabled Watson and Crick to formulate a
molecular model for DNA—a double helix, which can