Natural selection and the genetically encoded amino acid alphabet

Ilardo, Melissa Ann
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[Honolulu] : [University of Hawaii at Manoa], [May 2013]
Current science has advanced far beyond Crick's 'frozen accident' interpretation of the origin of the standard genetic code. Codon assignments can and do change, and new amino acids can be added to the code. Combined with the simple observation that the complex molecular machinery responsible for the standard code is a product of considerable evolution, it becomes legitimate and important to ask what else explains how and why one particular genetic code emerged within LUCA that still dominates the staggering diversity of life on our planet. Put another way, once we recognize the code as an evolvable phenomenon, we can ask what evolutionary forces shaped the emergence of the particular codon assignments found within the standard genetic code. Biological thinking has coalesced around three major ideas: the Adaptive Hypothesis, the Stereochemical Hypothesis, and the Biosynthetic or Co-Evolutionary Hypothesis. Assessing the validity of all three theories (and any further estimation of their relative contributions) depends upon further investigations of two fundamental assumptions. These assumptions relate to the two previously mentioned chemical languages between which the genetic code acts as an interface: nucleotides and amino acids. A plethora of nucleotides and amino acids formed through biotic and abiotic processes were available in abundance during the earliest stages of life's evolution, as will be addressed in detail in Chapter 2. For the purpose of concluding this review of ideas regarding the evolution of the standard genetic code, what matters is to notice that any estimates made as to the relative importance of the theories described in this chapter build from the assumption of four nucleotides to encode twenty amino acids.
M.S. University of Hawaii at Manoa 2013.
Includes bibliographical references.
amino acid
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