Linus Pauling: One day, when I was Eastman Professor at Oxford in the spring of 1948, I caught a cold. It was before the vitamin C days!
I caught a cold and after a day or two in bed of reading science fiction and detective stories, I got tired of that, and thought,
why don't I discover the alpha helix? Something like that - why don't I try to find how polypeptide chains are folded in a
way compatible with all the knowledge we have of structural chemistry and such that they can form hydrogen bonds to hold the
parts of the molecule together?
I took a piece of paper, much like this piece, and drew on it a representation of an extended polypeptide chain, with the
distances approximately right and the angles right. Except, one angle did not have the right value. I still have that original
piece of paper, by the way. This is the bond angle of the alpha carbon that didn't have the right value. I folded the paper
- actually, it took several trials - I folded it along several parallel lines through the successive alpha carbons.
Finally, I found a way by folding the paper to make this bond have an angle of 110 degrees. I finally found a way of folding
such that when I fit it together, there was an N-H-C-O bond formed by each N-H group, and each C=O group. The hydrogen bond
held the structure together and had just the right dimensions. I found that this structure, which turned out to be the structure
of hair and horn and fingernail, and also present in myoglobin and hemoglobin and other globular proteins, a structure called
the alpha-helix, had 3.6 residues per turn of the helix. A helical structure where there are 3.6 residues per turn.
