Abstract
The early metabolism arising in a Thioester world gave rise to amino acids and their simple peptides. The catalytic activity of these early simple peptides became instrumental in the transition from Thioester World to a Phosphate World. This transition involved the appearances of sugar phosphates, nucleotides, and polynucleotides. The coupling of the amino acids and peptides to nucleotides and polynucleotides is the origin for the genetic code. Many of the key steps in this transition are seen in the catalytic cores of the nucleotidyltransferases, the class II tRNA synthetases (aaRSs) and the CCA adding enzyme. These catalytic cores are dominated by simple beta hairpin structures formed in the Thioester World. The code evolved from a proto-tRNA, a tetramer XCCA interacting with a proto-aminoacyl-tRNA synthetase (aaRS) activating Glycine and Proline. The initial expanded code is found in the acceptor arm of the tRNA, the operational code. It is the coevolution of the tRNA with the aaRSs that is at the heart of the origin and evolution of the genetic code. There is also a close relationship between the accretion models of the evolving tRNA and that of the ribosome.
Highlights
There are two competing theories for the origin of life that are based on Darwinian selection; the RNA World and the Clay World
The Class II synthetases are considered to be older than the Class I synthetases. This is based on the fact that the majority of the hydrophobic amino acids are activated by class I synthetases and were unlikely to have been available for early polymerization, while Glycine, Alanine, Proline, and Aspartic acid were available. The evidence for this is based on the metabolic metric, which orders the entry of the amino acids into the genetic code by counting the number of catalytic steps involved in the biosynthesis of the amino acid from the reverse citric acid cycle [12]
Thioester-dependent peptide synthesis, functionally similar to the present-day non-ribosomal peptide synthesis by multi-enzyme thiol-template systems” [16]. This finding is consistent with a recent example of an atypical Seryl-tRNA synthetase found in a methanogenic Archaea, which lacks a tRNA binding site and instead transfers the activated amino acid (Aminoacyl-AMP) to a sulfhydryl group found on the phosphopantetheine which is bound to a carrier protein forming a Thioester
Summary
There are two competing theories for the origin of life that are based on Darwinian selection; the RNA World and the Clay World. They both assume a replicating and a mutating entity that has catalytic capacity. The waters of the hot spring included transition-state metal ions (i.e., Mn, Cu, Zn), adding to the catalytic capabilities of the iron-rich clays. These self-replicating clays would photochemically fix CO2 into organic acids and gradually evolve into the sulfide-rich region acquiring N2 fixation in the process. If we apply the method of the onion heuristic view, it can be conjectured that the citric acid cycle came first and was followed by the amino acids, lipids, nucleotides, and carbohydrates
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
