The Interplay Of Metabolic Kinetics And Aggregate Thermodynamics In Protocell Growth And Division
Chad Knutson, Los Alamos National Laboratory
A significant challenge in developing minimal artificial living systems is an appropriate coupling of the thermodynamics and the kinetics of the involved physico-chemical processes. We are interested in understanding how the rate of metabolic processes influences the growth and division of minimal artificial cells, or protocells, as described by Rasmussen and Chen [Science 303 (2004) 963–965]. The protocell consists of amphiphilic molecules that form a micellar container. In the interior of the micelle, hydrophobic precursor molecules are metabolically transformed into amphiphilic molecules by light-induced electron transfer reactions catalyzed by a sensitizer molecule. We first present an analysis of the reaction kinetics of the involved photo-fragmentation reactions and show how two different analytical solutions can be obtained depending on the details of the rate-limiting step. We then use dissipative 3-D particle dynamics (DPD) to represent the dynamics of a protocell in an aqueous environment. Not surprisingly, the 3-D simulation reveals additional reaction kinetic details. The DPD simulation suggests that for fast metabolic amphiphile production, the protocell is indeed able to divide and form daughter cells. This is possible because of an instability induced by the rapid increase in boundary molecules and therefore area, coupled with a rapid decrease of the hydrophobic volume. In contrast, for slow amphiphile production rate, the new amphiphiles move to the surface and displace excess amphiphiles to the surrounding solution thus preventing cell division. This work provides guidance for determining the necessary experimental metabolic rates required to drive the division of a minimal artificial cell.
This work is supported in part by the Los Alamos sponsored Protocell Assembly LDRD-DR and the European Commission sponsored Programmable Artificial Cell Evolution (PACE) projects.