2014 Annual Science Report
University of Illinois at Urbana-Champaign Reporting | SEP 2013 – DEC 2014
Project 3: The Origin of Homochirality
A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. We are calculating the way in which this can take place using statistical mechanics, and also trying to see how a uniform homochirality could be stable to spatial fluctuations.
A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. For this argument to be viable, it has to be shown that autocatalysis can indeed amplify homochirality. Secondly, one must consider the potentially confounding effects of spatial extension, which could give rise to spatial heterogeneity in the pattern of chiral symmetry breaking. We have succeeded in providing an improved formulation of the famous homochirality model of F.C. Frank, one that removes an unphysical requirement and moreover includes the inevitable and important stochasticity arising from chemical reactions. The mathematics shows that homochirality can arise by a previously unnoticed mechanism – the stabilization of homochirality into states that are least affected by noise. This mechanism is different from potential-based mechanisms for bistability, because it is the noise itself that generates the symmetry breaking. We have also succeeded in formulating this stochastic model with spatial extension. Our preliminary result is that the autocatalytic mechanism for homochirality does not seem to be stable in space: life would self-organize into local domains where homochirality was present, but of a different sign in neighbouring domains. If our ongoing research confirms this result, then it will cast doubt on the autocatalytic proposal for homochirality.
PROJECT MEMBERS:Nigel Goldenfeld
RELATED OBJECTIVES:Objective 3.2
Origins and evolution of functional biomolecules
Origins of cellularity and protobiological systems
Earth's early biosphere.
Production of complex life.
Environment-dependent, molecular evolution in microorganisms
Co-evolution of microbial communities
Biosignatures to be sought in Solar System materials
Biosignatures to be sought in nearby planetary systems