Linus Pauling and the Alpha-Helix




Linus Pauling was the foremost American chemist of his day.  He is considered to be one of the first to apply the new quantum mechanical views of physics to problems of chemistry, which led to the idea of resonance.  His wide-ranging research included the nature of the chemical bond, and he published a book by the same title in 1939, which Watson and Crick relied upon for chemical information when they set about to determine the structure of DNA.

Pauling's work represents the second major approach that fused into molecular biology (the first was the functional approach of the biochemists (e. g., Avery and Chargaff) and the geneticists (e. g., Delbruck and the Phage Group).  Thus, Pauling is  signficant for providing Watson and Crick with the basic approach they used in solving the structure of DNA--model-building.  In 1948, while in bed recovering from a cold, Pauling playfully constructed a crude paper model of a polypeptide chain using the chemical and stereochemical constraints known at that time--such as, that the peptide bond was a flat (planar) shape.  He concluded that the polypeptide chain was a single-stranded helix, which he named the alpha-helix.  He won the Nobel prize in chemistry for this in 1954.

The rivalry between Pauling and W. L. Bragg forms the backdrop to the Watson and Crick story.  Back in the late 1920s, Pauling had beaten Bragg to the stereochemical and electrostatic rules that determined the structure of minerals.  And in 1951, soon after Bragg's Cavendish group failed miserably in their efforts to establish a structure for the polypeptide, Pauling triumphantly unveiled his alpha-helix, leaving it to the horrified Cavendish group to verify its correctness.  Pauling had to ignore a "fact" that had held back progress in the Cavendish group--namely, William Astbury's x-ray diffraction photograph that showed a spot that said a full turn of the helix would be 5.1 angstroms.  Pauling's theory said the height of the full turn was 5.4 angstroms, which turned out to be correct.  This ability to treat all "facts" with suspect was another insight that Watson and Crick gleaned from Pauling's success.