The Information - James Gleick [142]
Even before the exact answer was reached, Crick crystallized its fundamental principles in a statement that he called (and is called to this day) the Central Dogma. It is a hypothesis about the direction of evolution and the origin of life; it is provable in terms of Shannon entropy in the possible chemical alphabets:
Once “information” has passed into protein it cannot get out again. In more detail, the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible. Information means here the precise determination of sequence.♦
The genetic message is independent and impenetrable: no information from events outside can change it.
Information had never been writ so small. Here is scripture at angstrom scale, published where no one can see, the Book of Life in the eye of a needle.
Omne vivum ex ovo. “The complete description of the organism is already written in the egg,”♦ said Sydney Brenner to Horace Freeland Judson, molecular biology’s great chronicler, at Cambridge in the winter of 1971. “Inside every animal there is an internal description of that animal.… What is going to be difficult is the immense amount of detail that will have to be subsumed. The most economical language of description is the molecular, genetic description that is already there. We do not yet know, in that language, what the names are. What does the organism name to itself? We cannot say that an organism has, for example, a name for a finger. There’s no guarantee that in making a hand, the explanation can be couched in the terms we use for making a glove.”
Brenner was in a thoughtful mood, drinking sherry before dinner at King’s College. When he began working with Crick, less than two decades before, molecular biology did not even have a name. Two decades later, in the 1990s, scientists worldwide would undertake the mapping of the entire human genome: perhaps 20,000 genes, 3 billion base pairs. What was the most fundamental change? It was a shift of the frame, from energy and matter to information.
“All of biochemistry up to the fifties was concerned with where you get the energy and the materials for cell function,” Brenner said. “Biochemists only thought about the flux of energy and the flow of matter. Molecular biologists started to talk about the flux of information. Looking back, one can see that the double helix brought the realization that information in biological systems could be studied in much the same way as energy and matter.…
“Look,” he told Judson, “let me give you an example. If you went to a biologist twenty years ago and asked him, How do you make a protein, he would have said, Well, that’s a horrible problem, I don’t know … but the important question is where do you get the energy to make the peptide bond. Whereas the molecular biologist would have said, That’s not the problem, the important problem is where do you get the instructions to assemble the sequence of amino acids, and to hell with the energy; the energy will look after itself.”
By this time, the technical jargon of biologists included the words alphabet, library, editing, proofreading, transcription, translation, nonsense, synonym, and redundancy. Genetics and DNA had drawn the attention not just of cryptographers but of classical linguists. Certain proteins, capable of flipping from one relatively stable state to another, were found to act as relays, accepting ciphered commands and passing them to their neighbors—switching stations in three-dimensional communications networks.