A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code

TL;DR

This paper demonstrates that thermodynamics can predict the relative abundance of early amino acids in prebiotic conditions, supporting theories of stepwise genetic code evolution and universal early biochemistry.

Contribution

It introduces a thermodynamic framework to explain amino acid abundances and the evolution of the genetic code from prebiotic chemistry data.

Findings

Thermodynamics predicts amino acid abundance order in prebiotic contexts.

Early amino acids reflect the composition of first proteins.

Stepwise addition of amino acids aligns with genetic code evolution theories.

Abstract

Of the twenty amino acids used in proteins, ten were formed in Miller's atmospheric discharge experiments. The two other major proposed sources of prebiotic amino acid synthesis include formation in hydrothermal vents and delivery to Earth via meteorites. We combine observational and experimental data of amino acid frequencies formed by these diverse mechanisms and show that, regardless of the source, these ten early amino acids can be ranked in order of decreasing abundance in prebiotic contexts. This order can be predicted by thermodynamics. The relative abundances of the early amino acids were most likely reflected in the composition of the first proteins at the time the genetic code originated. The remaining amino acids were incorporated into proteins after pathways for their biochemical synthesis evolved. This is consistent with theories of the evolution of the genetic code by stepwise addition of new amino acids. These are hints that key aspects of early biochemistry may be universal.