The origin of biomolecular asymmetry – Insights from cometary and meteoritic matter

Abstract

The chemistry of life is purely stereospecific. The fundamental biopolymers – proteins and nucleic acids – are intrinsically chiral due to their molecular building blocks, namely L-amino acids and D-sugars. Hypotheses for the evolutionary origin of that strict stereochemical selection include the asymmetric photochemistry model by which circularly polarized (CP) photons induced an enantiomeric excess in chiral organic molecules via asymmetric photolysis. The transfer of a distinct chirality from chiral photons to organic molecules is assumed to have occurred in environments of interstellar molecular clouds. This model is strengthened by the observation of CP light in the star-forming region of Orion. Due to our laboratory experiments mimicking cometary ice evolution, we show that molecules of prebiotic interest such as amino and diamino acids are formed in inter/protostellar environments and might have been subjected to CP vacuum-UV radiation before and during their space journey to the early Earth.