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Videos
The DNA Story - 1973
 Linus Pauling recounts his discovery of the alpha helix and his work on DNA
Author: Linus Pauling
Length: 2:40
 Watch using MPG Size: 20.9MB
Transcript:
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.
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