title: A theory of the origin of life.
abstract: Life on Earth is essentially nucleic acids (NAs) influencing peptide synthesis such that NA replication is favored. It is proposed that the ability to synthesize polypeptides evolved gradually - one peptide bond at a time. The proposed evolution of the peptide synthesis apparatus begins with a 'transfer NA' (tNA) which catalyzes the transfer of activated amino acids to accessible amino groups in its environment. The resulting 'capped molecules' (with single amino acid 'caps') in turn favor NA replication. The proposed evolution of the peptide synthesis apparatus from the tNA onward is characterized by a progressive increase in the number of amino acids per cap: two tNAs jointly produce a 'dipeptide cap', three tNAs jointly produce a 'tripeptide cap', etc. Messenger NAs evolve because they can specify the composition and sequence order of the peptide caps. Lastly, ribosomal NAs evolve. The origin, expansion, and standardization of the genetic code are discussed. It is proposed that the presence triplet code evolved by a process of codon length refinement, and the originally codons of varying lengths were allowable, as were unassigned bases between codons. An environmental supply of activated compounds for early evolving entities is proposed. An 'environmental retention and redistribution process' is proposed to have acted as a functional substitute for the cell wall and cell division of early evolving entities.
mesh_terms: D000596:Amino Acids; D005075:Biological Evolution; D002455:Cell Division; D002473:Cell Wall / Q000502:physiology; D004261:DNA Replication; D004734:Energy Metabolism; D005815:Genetic Code; D008954:Models, Biological; D009696:Nucleic Acids; D000069497:Origin of Life; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D012343:RNA, Transfer; D013698:Templates, Genetic
chemical_list: D000596:Amino Acids; D009696:Nucleic Acids; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D012343:RNA, Transfer