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Nucleic acid-base balance.

It was now known that nucleic acids were large and very complex molecules, especially since Avery had shown that deoxyribonucleic acid (DNA) and not protein was the carrier of physical characteristics (see 1944). It was DNA, in short, that made up the genes of the chromosomes.

The question was: Just what was it about the structure of nucleic acids that made it possible for them to carry the vast amount of information that genes must carry in order to make human eggs develop into human beings and grasshopper eggs into grasshoppers, without the reverse ever happening? Part of the structure of DNA was known to be four different bases. Two of them (adenine and guanine) were purines with a two-ring molecule, and two of them (cytosine and thymine) were pyrimidines with a one-ring molecule.

The Austrian-born American biochemist Erwin Chargaff (b. 1905) broke down nucleic acid molecules to their constituent bases and separated them by paper chromatography. He determined the quantity of each present and by 1948 was able to demonstrate than, in nucleic acids generally, the number of guanine units was equal to the number of cytosine units, and the number of adenine units was equal to the number of thymine units. This meant that the number of purine units was equal to the number of pyrimidine units.

This was a more important discovery than Chargaff apparently realized at the time, and he did not follow it up properly.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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