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On the possible origin and evolution of the genetic codeThe genetic code is examined for indications of possible preceding codes that existed during early evolution. Eight of the 20 amino acids are coded by 'quartets' of codons with fourfold degeneracy, and 16 such quartets can exist, so that an earlier code could have provided for 15 or 16 amino acids, rather than 20. If twofold degeneracy is postulated for the first position of the codon, there could have been ten amino acids in the code. It is speculated that these may have been phenylalanine, valine, proline, alanine, histidine, glutamine, glutanic acid, aspartic acid, cysteine and glycine. There is a notable deficiency of arginine in proteins, despite the fact that it has six codons. Simultaneously, there is more lysine in proteins than would be expected from its two codons, if the four bases in mRNA are equiprobable and are arranged randomly. It is speculated that arginine is an 'intruder' into the genetic code, and that it may have displayed another amino acid such as ornithine, or may even have displayed lysine from some of its previous codon assignments. As a result, natural selection has favored lysine against the fact that it has only two codons.
Document ID
19740058785
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Jukes, T. H.
(California, University Berkeley, Calif., United States)
Date Acquired
August 7, 2013
Publication Date
October 1, 1974
Publication Information
Publication: Origin of Life
Volume: 5
Subject Category
Biosciences
Accession Number
74A41535
Funding Number(s)
CONTRACT_GRANT: NGR-05-003-460
Distribution Limits
Public
Copyright
Other

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