Origin of organic compounds on the primitive earth and in meteorites

Abstract

The role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth, in the parent bodies or carbonaceous chondrites, and in the solar nebula are examined. A single source of energy or a single process would not account for all the organic compounds synthesized in the solar system. Electric discharges appear to produce amino acids more efficiently than other sources of energy and the composition of the synthesized amino acids is qualitatively similar to those found in the Murchison meteorite. Ultraviolet light is also likely to have played a major role in prebiotic synthesis. Although the energy in the sun's spectrum that can be absorbed by the major constituents of the primitive atmosphere is not large, reactive trace components such as H2S and formaldehyde absorb at longer wavelengths where greater amounts of energy are available and produce amino acids by reactions involving hot hydrogen atoms. The thermal reaction of CO + H2 + NH3 on Fischer-Tropsch catalysts generates intermediates that lead to amino acids and other organic compounds that have been found in meteorites. However, this synthesis appears to be less efficient than electric discharges and to require a special set of reaction conditions. It should be emphasized that after the reactive organic intermediates are generated by the above processes, the subsequent reactions which produce the more complete biochemical compounds are low temperature homogenous reactions occurring in an aqueous environment.

Imprints of the genetic code in the ribosome

“…Empirical data, although limited in the past, has yielded landmark insights. The spark-tube experiments confirmed that amino acids could have been produced abiotically in the atmosphere of the early earth (27,35), and in vitro RNA aptamer selections provided solid evidence for the association of coding triplets with cognate amino acids (28). Our usage of ribosome structural data further demonstrates the usefulness of expanding the theoretical inputs to a biological context.…”

“…However, because primitive life before LUCA and LUCA itself do not exist today for comparative study, evidence for codon reassignments during the canonical code formation is lacking. Our results, obtained through analyzing ribosomal structural The chronological order of amino acid addition to the code is shown, as well as the amino acids that are thought to have been prebiotically available in the Miller-Urey experiments (27). The amino acids with significant enrichment of anticodon-containing rRNA in ribosome structures are later additions to the genetic code.…”

“…We therefore tentatively place lysine in the population of those amino acids with an anticodon interaction. The two-stage distribution suggests that ancient amino acids implied in the Miller-Urey experiment (27) were fixed into the genetic code through means other than amino acid-anticodon interaction, or that such interactions were masked in the ribosome because of later codon reassignment upon addition of new amino acids. Newer amino acids, on the other hand, were added to the genetic code mainly through the anticodon interaction.…”

<b>A teleologia e a aleatoriedade no estudo das ciências da natureza: sistemas, ontologia e evolução</b><br>DOI:10.5007/1807-1384.2011v8n2p316

“…Em vista das exigências químicas Miller et al (1976) implica a concepção filosófica de uma força vital, ao mesmo tempo imanente e transcendente em relação a cada um dos organismos vivos. Imanente por existir personificada nesses organismos e transcendente por procurar realizar-se não apenas na perpetuação do seu tipo específico, e sim por estar sempre tentando encontrar, por si mesma, uma realização mais adequada num novo tipo.…”

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

“…Crustal radioactivity has been considered 'probably not an important energy source for the synthesis of organic compounds on the primitive Earth' (Miller et al, 1976). However, like cosmic irradiation, energetic particles from heavy radioelements (uranium, thorium) can cause the polymerisation of organic molecules.…”