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Three stages during the evolution of the genetic codeA diversification of the genetic code based on the number of codons available for the proteinous amino acids is established. Three groups of amino acids during evolution of the code are distinguished. On the basis of their chemical complexity and a small codon number those amino acids emerging later in a translation process are derived. Both criteria indicate that His, Phe, Tyr, Cys and either Lys or Asn were introduced in the second stage, whereas the number of codons alone gives evidence that Trp and Met were introduced in the third stage. The amino acids of stage one use purines rich codons, thus purines have been retained in their third codon position. All the amino acids introduced in the second stage, in contrast, use pyrimidines in this codon position. A low abundance of pyrimidines during early translation is derived. This assumption is supported by experiments on non enzymatic replication and interactions of DNA hairpin loops with a complementary strand. A back extrapolation concludes a high purine content of the first nucleic acids which gradually decreased during their evolution. Amino acids independently available form prebiotic synthesis were thus correlated to purine rich codons. Conclusions on prebiotic replication are discussed also in the light of recent codon usage data.
Document ID
19950032218
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Baumann, U.
(NASA Ames Research Center Moffett Field, CA, US, United States)
Oro, J.
(University of Houston, Houston, TX US, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1994
Publication Information
Publication: Origins of Life and Evolution of the Biosphere
Volume: 24
Issue: 2-4
ISSN: 0169-6149
Subject Category
Life Sciences (General)
Accession Number
95A63817
Distribution Limits
Public
Copyright
Other

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