Abstract
Life on Earth and the genetic code evolved around tRNA and the tRNA anticodon. We posit that the genetic code initially evolved to synthesize polyglycine as a cross-linking agent to stabilize protocells. We posit that the initial amino acids to enter the code occupied larger sectors of the code that were then invaded by incoming amino acids. Displacements of amino acids follow selection rules. The code sectored from a glycine code to a four amino acid code to an eight amino acid code to an ~16 amino acid code to the standard 20 amino acid code with stops. The proposed patterns of code sectoring are now most apparent from patterns of aminoacyl-tRNA synthetase evolution. The Elongation Factor-Tu GTPase anticodon-codon latch that checks the accuracy of translation appears to have evolved at about the eight amino acid to ~16 amino acid stage. Before evolution of the EF-Tu latch, we posit that both the 1st and 3rd anticodon positions were wobble positions. The genetic code evolved via tRNA charging errors and via enzymatic modifications of amino acids joined to tRNAs, followed by tRNA and aminoacyl-tRNA synthetase differentiation. Fidelity mechanisms froze the code by inhibiting further innovation.
Highlights
This report, underlying the RNA world hypothesis, we find the hypothesis is enriched by focus on focuses the RNA world approach on generation of tRNA and the genetic code
The working model is built on a simple set of ideas: (1) glycine was the first encoded amino acid, and at an early stage, all anticodons and all codons encoded glycine; (2) amino acids were added to the code via invasion of occupied sectors; (3) the genetic code evolved around the tRNA anticodon; (4) the final sectoring structure of the code depended strongly on the order of additions of amino acids; and (5)
The genetic code complexity was determined by how the tRNA anticodon
Summary
Without tRNA, no complex life supported by genetic coding could evolve. LUCA (the last universal common cellular ancestor) indicates the first cells and the first intact DNA genomes. Once the genetic code evolved, synthesis of RNA-encoded proteins was possible, and complex life on Earth became inevitable. Figure1.1.AAmodel modelfor forevolution evolution translation systems first cells. A small number of ribozymes appears sufficient to generate tRNA from pre-tRNA sequences the first cells. Sequences thatbecause are known because theyinare conserved in tRNAs. Evolution to evolution translation systems and the genetic code. LUCA, last universal common cellular was published [1] and is published reprinted here version of thisin figure was in [1]with and permission.
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