Tuesday, February 15, 2005


One of the accomplishments of living systems which is, of course, quite without any analogy in the field of our own technology is their capacity for self-duplication. With the dawn of the age of computers and automation after the Second World War, the theoretical possibility of constructing self-replicating automata was considered seriously by mathematicians and engineers. Von Neumann discussed the problem at great length in his famous book Theory of Self-Reproducing Automata, but the practical difficulties of converting the dream into reality have proved too daunting. As Von Neumann pointed out, the construction of any sort of self-replicating automaton would neces sitate the solution to three fundamental problems: that of storing information; that of duplicating information; and that of designing an automatic factory which could be programmed from the infor mation store to construct all the other components of the machine as well as duplicating itself. The solution to all three problems is found in living things and their elucidation has been one of the triumphs of modern biology.

So efficient is the mechanism of information storage and so elegant the mechanism of duplication of this remarkable molecule that it is hard to escape the feeling that the DNA molecule may be the one and only perfect solution to the twin problems of information storage and duplication for self-replicating automata.

The solution to the problem of the automatic factory lies in the ribosome. Basically, the ribosome is a collection of some fifty or so large molecules, mainly proteins, which fit tightly together. Altogether the ribosome consists of a highly organized structure of more than one million atoms which can synthesise any protein that it is instructed to make by the DNA, including the particular proteins which compromise its own structure — so the ribosome can construct itself!

The protein synthetic apparatus is also, however, the solution to an even deeper problem than that of self-replication. Proteins can be designed to perform structural, logical, and catalytic functions. For instance, they form the impervious materials of the skin, the contractile elements of muscles, the transparent substance of the lens of the eye: and, because of their practically unlimited potential, almost any conceivable biochemical object can be ultimately constructed using these remarkable molecules as basic structural and functional units. The choice of the protein synthetic apparatus as the solution to the problem of the automatic factory has deep implications. Not only does it represent a solution to one of the problems of designing a self- duplicating machine but it also represents a solution to an even deeper problem, that of constructing a universal automaton. The protein synthetic apparatus cannot only replicate itself but, in addition, if given the correct information, it can also construct any other biochemical machine, however great its complexity, just so long as its basic functional units are comprised of proteins, which, because of the near infinite number of uses to which they can be put, gives it almost limitless potential.

It is astonishing to think that this remarkable piece of machinery, which possesses the ultimate capacity to construct every living thing that ever existed on Earth, from a giant redwood to the human brain, can construct all its own components in a matter of minutes and weigh less than 10^16 grams. It is of the order of several thousand million million times smaller than the smallest piece of functional machinery ever constructed by man.

(Evolution: A Theory in Crisis
By Michael Denton :337-338)

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