Opus 100 by Isaac Asimov

Author:Isaac Asimov [Asimov, Isaac]
Language: eng
Format: epub
Tags: f.Anthology, g.Biography, g.Fiction, g.Nonfiction, g.Science Fiction/Fantasy
ISBN: 9780395073513
Google: UH5BAAAAIAAJ
Amazon: 0395073510
Goodreads: 3954117
Publisher: Houghton Mifflin
Published: 1969-05-15T04:00:00+00:00

from Biochemistry and Human Metabolism (1952)

In a very real sense, life may be looked upon as a struggle on the part of the body to maintain the internal structure of the enormously complex protein molecules of which it is composed. The difficult nature of such a task may be judged from the fact that a distinctive property of most protein molecules is their extreme instability as compared with other chemical structures. Environmental factors as mild as the warmth of a human hand or the gentle bubbling of air would suffice, in many cases, to so alter the properties of a protein solution as to render it biologically useless.

That life should be built on such fragile, almost evanescent, molecules is not at all surprising. It would seem, upon reflection, to be inevitable. Life implies change—quick adjustments to altered conditions. There must be something then in a living organism which can vary with the absorption of a few quanta of light, with trifling changes in air pressure, oxygen concentration, temperature, or any of the other hundreds of variables that beset us every moment of time. That something is the protein molecule.

It might be tempting for beginning students to equate complexity of structure with mere size of molecules. Thus, the beta-lactoglobulin of milk has an empirical formula which is thought to be C1864H3012N468S21O576. Here we have a molecule in which we can count almost six thousand individual atoms of five different kinds. The molecular weight is over forty thousand, which means that the molecule is some twenty-three hundred times as heavy as a water molecule and more than two hundred times as heavy as a molecule of the amino acid, tryptophane. And yet beta-lactoglobulin is a protein of comparatively simple structure. Certainly, its molecular weight is well below the average for proteins.

Molecular weights in the hundreds of thousands are common and those in the millions are not unknown. There are protein molecules, in other words, which compare with beta lactoglobulin as that protein compares with tryptophane.

Yet, knowing size, we know comparatively little. There are other types of molecules produced by living organisms which compare with proteins in molecular weight. There is cellulose, for instance, impressive in size, and yet used for nothing more in the living plant than to enclose the cell in a sturdy box. It is a huge molecule, yet so stable that we build houses out of it. Size alone is therefore no guarantee that a molecule will possess the flexibility and instability needed to have within it the potentiality of life.

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