Whicher, AL; (2016) Simulated alkaline hydrothermal vent environments to investigate prebiotic metabolism at the origin of life. Doctoral thesis , UCL (University College London).

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Abstract

There is still little agreement today about where life may have started on Earth. Prebiotic studies over several decades have successfully synthesised many molecules of life, yet the results display strikingly little congruence to the biochemistry of cells today. In contrast, alkaline hydrothermal vents offer conditions very similar to those harnessed by modern autotrophic cells, while providing a physical structure for a prebiotic metabolism that resembles the vectorial biochemistry of extant cells. Alkaline vents have not received much attention in experimental investigations, even though they have many features that point to their ability to drive prebiotic chemistry. This study set out to simulate inorganic, catalytic barriers equivalent to those that are thought to have existed inside early alkaline vent systems. These structures were then used to investigate the reduction of CO2 by H2, driven by natural proton gradients transecting semi-conducting barriers containing catalytic FeS minerals. Simple organics such as formaldehyde were successfully synthesised and observed to be closely associated with the precipitates. The next step examined potential prebiotic reactions that could have preceded modern metabolic processes. Methyl thioacetate and thioacetic acid have been suggested as possible precursors of acetyl-coenzyme A, therefore its synthesis from the 1-carbon precursors methyl sulphide and formate was attempted. Finally the synthesis of a plausible prebiotic analogue of ATP, acetyl phosphate, was demonstrated from the 2-carbon precursor thioacetate under ambient and mild hydrothermal conditions. Acetyl phosphate was shown to drive both phosphorylation and condensation reactions equivalent to ATP, in water, notably the formation of two key activated precursors of RNA synthesis, ribose phosphate and adenosine monophosphate. The results suggest that alkaline hydrothermal systems could indeed drive the beginnings of a prebiotic metabolism more congruent with living cells, and point to future research into this hypothesis.

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