Dr. Nita Sahai of the University of Akron, will give a talk at Speakers Club entitled From Geochemistry to Biogeochemistry: The Potential Roles of Minerals in Protocell Emergence.

Abstract

Life originated on Earth ~ 4.4 - 3.5 Ga through processes in which simple organic compounds, supplied by the environment, self-organized into “protocells.” For the present purposes, a protocell or minimal cell is defined as an entity enclosed by a lipid membrane, and which is capable of both replication with hereditary mutation and of metabolic cycles for self-maintenance. In extant biology, the synthesis of lipids, replication, and metabolic processes are catalyzed by enzymes, which are themselves produced by the cells, creating a chicken-and-egg problem. Before biology, what could have catalyzed these reactions? Since water is essential to life the emergence of protocells probably occurred at the mineral/water interface. Mineral surfaces could have played a role in affecting the thermodynamic stability and/or in catalyzing the reactions resulting in the origins of life, thus facilitating the transition from geochemistry to bio(geo)chemistry.

The focus of today’s seminar is on studies investigating whether minerals could have affected the stability of protocell membranes. Model membranes composed of fatty acid vesicles were synthesized in the presence of various minerals, and their critical vesicle formation constant, permeability, and rate of formation were determined. Mineral chemical composition, surface charge, solubility, specific surface area, particle size, and particle loading were considered  to determine if vesicle stability and integrity could be be related to these mineral properties. Negatively charged minerals had no effect on membranes, positively charged minerals promoted vesicle formation rate. Cations leached from minerals at low loading promoted vesicle formation rate, but entirely destabilized the vesicles at higher loadings. Thus, minerals may have acted as an environmental selection pressure on survival of the fittest protocells.