Behaviour of RNA under hydrothermal conditions and the origins of life

Abstract

The RNA world hypothesis and the hydrothermal origin of life hypothesis are contradictory to each other. Although it is considered that RNA molecules are too labile to maintain life-like systems at high temperatures and there is extensive literature on nucleic acid hydrolysis, the stability and the chemical evolution of RNA have not been sufficiently analysed from the viewpoint of hydrothermal reactions. Based on our experimental data concerning the stability and the prebiotic formation of RNA at high temperatures, two different aspects seem to be important for evaluating whether RNA molecules are too labile. First, the stability of RNA molecules should be evaluated from the comparison of the rate of formation and the rate of degradation of RNA in open systems. Our prebiotic reaction models of phosphodiester bond formation suggest that at high temperatures the accumulation of RNA may be possible. However, an RNA world entirely consisting of RNA molecules is unlikely to occur because the biologically important interactions are not effective for the bare RNA molecules at high temperatures. Second, since enzymes presently mediate most biological reactions, evaluation of the accumulation of RNA should be based on the comparison between the enzymatic and non-enzymatic reaction rates. Hence, the evaluation of the primitive enzymatic reaction rates at high temperatures has been attempted. There is a large difference between the present enzymatic reaction rates at 25-90 xC and the non-enzymatic reaction rates at high temperatures of 200-300 xC. It is thus possible that prebiotic enzyme-like assemblies could have facilitated the accumulation of RNA molecules at hydrothermal vent temperatures.

Lipid-assisted Synthesis of RNA-like Polymers from Mononucleotides

“…A certain amount of hydrolysis presumably does occur in the hydrated stage of a cycle, but when mononucleotides are present the forward reaction of phosphodiester bond synthesis would also occur in the anhydrous stage, with the net effect of preserving longer polymers. Kawamura and colleagues investigated the formation and stability of phosphodiesters bond at elevated temperatures (Kawamura et al 1997;Kawamura 2004). Their findings show that net synthesis of oligonucleotides from activated mononucleotides can occur at 100°C because rates of formation of phosphodiester bonds at elevated temperatures exceed hydrolysis rates.…”

“…Several studies have investigated possible pathways for the synthesis and degradation of RNA under hydrothermal conditions (White 1984;Larralde et al 1995;Miller and Lazcano 1995;Kawamura et al 1997;Levy and Miller 1998;Kawamura 2004). Kawamura's results suggest that it is possible for synthesis of phosphodiester bonds to occur in hot aqueous solutions if chemically activated monomers and catalysts are present.…”

Kinetic Analysis of Oligo(C) Formation from the 5′-Monophosphorimidazolide of Cytidine with Pb(II) Ion Catalyst at 10–75°C

“…According to these empirical data, it is considered that RNA molecules are too labile under hydrothermal vent conditions for these two hypotheses to be compatible (Kawamura 2004(Kawamura , 2005. Furthermore, biologically important weak interactions such as hydrophobic interactions and hydrogen bonding are weaker at higher temperatures (Kawamura 2005).…”

One-step formation of oligopeptide-like molecules from Glu and Asp in hydrothermal environments

“…Although the theory of proteinoid thermal synthesis under dry conditions on earth has been criticized due to the associated difficulties (Miller and Orgel 1974), the present study showed that similar condensations of oligopeptide-like molecules in an aqueous medium could have proceeded under hydrothermal conditions. Oligopeptides thus formed in hydrothermal vent systems could have survived within the surrounding cool (not hydrothermal) ocean water (Imai et al 1999;Kawamura 2004), and this is more probable than proteinoids surviving on the extremely hot surface of the earth. Because Glu and Asp are also considered to be important for the emergence of the genetic coding system, they may have played important roles in the accumulation of oligopeptide-like molecules on earth.…”