Nature's Robots: A History of Proteins

By Charles Tanford; Jaqueline Reynolds | Go to book overview

CHAPTER 21
After the double helix: the
triplet code

It is only within the past 15 years, however, that insight has been gained into the chemical nature of the genetic material and how its molecular structure can embody coded instructions that can be ‘read’ by the machinery in the cell responsible for synthesizing protein molecules. Francis Crick, 19661

The fact that DNA must be the carrier of genetic information had become universally accepted and the double-helical structure of DNA had shown, virtually by mere inspection of the structure, the probable mechanism by which the genetic material can be perpetuated, copied over and over again as cells divide. But these revelations did not immediately tell anyone how proteins are made: the difficult to sustain concept of protein templates disappeared from the scene, of course, but what was to take its place? Several good accounts of how the problem was solved were written in the mid-1960s, while actual events were still fresh in the writers’ minds. We make reference here to three that are suitable for the general reader.1–3


The sequence hypothesis

Combining the statement that DNA alone must be the self-perpetuating carrier of genetic information with the old ‘one gene, one enzyme’ principle leads to the at first rather astonishing conclusion that the sequence of bases in any section of cellular DNA—perpetuated by the complementarity of the double helix—must uniquely determine the sequence of amino acids in a corresponding polypeptide chain. This is Crick’s ‘sequence hypothesis’, as given in an anticipatory paper to an audience of biologists in 1958, not as an original idea of his own, but as a hypothesis that was already ‘rather widely held’.4 What is astonishing about it is that there was not at the

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