Saturday, March 13, 2010

"Hemoglobin and the Universe" (Only A Trillion)

According to Isaac Asimov's Essays, (a site that lists them and what books they are collected in, and reviews them, but doesn't go in-depth as ths blog does), "Hemoglobin and the Universe" first appeared in the February, 1955 issue of Astounding, and anthologized for the first and only time in 1957 in Only A Trillion.

The Quotable Asimov
Even the purest and most high-minded scientist finds it expedient sometimes to assault the fortress of truth with the blunt weapon of trial and error.

There is no question but that most or all of the secrets of life lie hidden in the details of protein structure.

First Paragraph
Even the purest and most high-minded scientist finds it expedient sometimes to assault the fortress of truth with the blunt weapon of trial and error. Sometimes it works beautifully. As evidence and as a case in point, let us bring to the front of the stage the hemoglobin molecule.

Topic
Hemoglobin is the chief protein component of the red blood cells.

Asimov goes on to tell of how the hemoglobin molecule is constructed - consisting of a heme fraction and a globin fraction. The heme fraction consists of an iron atom surrounded by twenty carbon atoms and four nitrogen atoms. The atoms are arranged in a "porphyrin ring."

Asimov explains how the structure of the porphyrin rings and their sidechains were discovered. (Asimov confinesa himself to simple arithmetic in his explanations, not chemistry.)

The discovery of the poryphirin ring construction for heme was done by trial and error - there were only 15 possible choices it could be. Asimov explains how German chemist Hans Fischer did it.

But what about for the protein, hemoglobin?

The rest of the essay is all mathematics, as Asimov explains why it would have been impossible to discover the structure of hemoglobin by the same trial and error method that had worked for heme.


Final Paragraph
How did the biochemists do it?

The fact is that straight trial-and-error technique would have been an unbearable trial and a colossal error. So they used other medthods. There are other methods, you know.

Note
The anthology, Only a Trillion, was published in 1957 with new material - the Notes, written in 1976. In his Note for this essay, Asimov points out:

Since this article was first written in July, 1954, chemists have discovered msany details about the hemoglobin molecule.

...

There is no longer any basic mystery as to how the body manufactures hemoglobin molecules, with all the amino acids correctly in place. In 1953, the year before this article was first written, James Watson and Francis Crick worked out the way in which the nucleic acid molecules of the chromosomes duplicated themselves. Other chemists went on to discover how the structure of the nucleic acids was used to guide the formation of chains of amino acids in a particular order. The basic details of all this you can find in my book The Genetic Code.

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