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Life 2015, 5(1), 181-211; doi:10.3390/life5010181

Emergent Chemical Behavior in Variable-Volume Protocells

ICREA-Complex Systems Lab, Institut de Biologia Evolutiva, CSIC-UPF, 08003 Barcelona, Spain
Logic and Philosophy of Science Department, University of The Basque Country, Avda. Tolosa 70, 20018 Donostia-San Sebastian, Gipuzkoa, Spain
Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA
Biophysics Unit (CSIC, UPV/EHU), University of The Basque Country, Barrio Sarriena s/n, 48940 Leioa, Bizkaia, Spain
Author to whom correspondence should be addressed.
Academic Editors: Fabio Mavelli and Pasquale Stano
Received: 14 October 2014 / Accepted: 4 January 2015 / Published: 13 January 2015
(This article belongs to the Special Issue Protocells - Designs for Life)
View Full-Text   |   Download PDF [1444 KB, uploaded 13 January 2015]   |  


Artificial protocellular compartments and lipid vesicles have been used as model systems to understand the origins and requirements for early cells, as well as to design encapsulated reactors for biotechnology. One prominent feature of vesicles is the semi-permeable nature of their membranes, able to support passive diffusion of individual solute species into/out of the compartment, in addition to an osmotic water flow in the opposite direction to the net solute concentration gradient. Crucially, this water flow affects the internal aqueous volume of the vesicle in response to osmotic imbalances, in particular those created by ongoing reactions within the system. In this theoretical study, we pay attention to this often overlooked aspect and show, via the use of a simple semi-spatial vesicle reactor model, that a changing solvent volume introduces interesting non-linearities into an encapsulated chemistry. Focusing on bistability, we demonstrate how a changing volume compartment can degenerate existing bistable reactions, but also promote emergent bistability from very simple reactions, which are not bistable in bulk conditions. One particularly remarkable effect is that two or more chemically-independent reactions, with mutually exclusive reaction kinetics, are able to couple their dynamics through the variation of solvent volume inside the vesicle. Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account. View Full-Text
Keywords: semi-permeable compartments; osmosis; variable solvent volume; mass action kinetics (MAK); chemical reactor; continuous-flow stirred tank reactor (CSTR); bistability; systems chemistry; osmotic coupling semi-permeable compartments; osmosis; variable solvent volume; mass action kinetics (MAK); chemical reactor; continuous-flow stirred tank reactor (CSTR); bistability; systems chemistry; osmotic coupling

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Shirt-Ediss, B.; Solé, R.V.; Ruiz-Mirazo, K. Emergent Chemical Behavior in Variable-Volume Protocells. Life 2015, 5, 181-211.

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