Seeking Signs of Minimal Evolution in a Protocell Model
Protocells are minimal organisms—individualized entities with an internal metabolism and an external boundary, which navigate the world and maintain their viability. An understanding of their organization behavior can provide a foundation for understanding the organization of more complex organisms and their behavior.
The origin of life on Earth could have been marked by a fundamental transition in the mode of chemical behavior—with the emergence of self-sustaining, replicating entities driven by Darwinian selection. Protocells have been proposed as the simplest examples of such entities, which can act as transition points from pure chemistry into the living domain. They consist of boundary membranes that contain a set of metabolic chemical reactions, whose operation builds specific molecules (amphiphiles) that in turn self-assemble as the membranes—the coupled activity of metabolism and membrane creates the conditions for their joint persistence. Protocells that grow and divide can generate a variable population, due to imperfect replication resulting from division. Darwinian selection immediately takes effect, as protocells are precarious structures and some will disintegrate while others survive. This basic mechanism drives the protocell population toward configurations of increased diversity and complexity.
It is a compelling scenario, but we do not know how this transition might have occurred, or what underlying principles would have been responsible. In this project, we advance our understanding by developing computational models of protocells that undergo growth and division. The model protocells are rooted in a virtual chemistry, with simulated molecules that move through space according to chemical principles such as diffusion, intermolecular forces, and reactions. By identifying the conditions under which these molecules self-organize into protocell structures, grow, and divide, we can probe this complex, but key, transition. By characterizing the structure and dynamics of stable protocells, we will seek signs of rudimentary evolution.
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