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Emergent chemical behavior in variable-volume protocells.

Shirt-Ediss B, Solé RV, Ruiz-Mirazo K - Life (Basel) (2015)

Bottom Line: 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.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.Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

View Article: PubMed Central - PubMed

Affiliation: ICREA-Complex Systems Lab, Institut de Biologia Evolutiva, CSIC-UPF, 08003 Barcelona, Spain. ben@shirt-ediss.me.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Chemical Reactor Models. (a) A chemical reaction held far-from-equilibrium by use of two constant concentration reservoirs (reservoir conditions). (b) Continuous-flow stirred tank reactor (CSTR) model with non-limiting outflow, constant solvent volume and constant reaction temperature. (c) Unilamellar lipid vesicle, with variable internal solvent volume determined by osmotic water flow equalizing the total solute concentration difference across the semi-permeable membrane. (d) Lipid vesicle morphology space, with vesicle viability space drawn as the sub-region of all possible morphologies (grayscale region). Axes express vesicle volume Ω and surface area Sµ as the nm diameter of a sphere having volume Ω or surface area Sµ, respectively. Spherical vesicles (Φ = 1) are located when Ω (in nm)= Sµ (in nm). Circles represent vesicle cross-sections, drawn to scale (8.5% of the axes’ scale). Blue crosses indicate how the morphology of a spherical d = 800 nm giant unilamellar vesicle (GUV) changes, when (i) gaining surface or (ii) losing volume. Both conditions bring the vesicle toward more filamentous or prolate states. Prolate states are depicted as strings of smaller spherical vesicles, only to give an idea of the volume and surface ratio at the {Ω, Sµ} point; the meaning is not that the vesicle has necessarily divided into identical daughters at this stage. Red crosses indicate that the spherical d = 800 nm vesicle will burst by (iii) losing too much surface or, conversely, (iv) gaining too much volume.
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life-05-00181-f001: Chemical Reactor Models. (a) A chemical reaction held far-from-equilibrium by use of two constant concentration reservoirs (reservoir conditions). (b) Continuous-flow stirred tank reactor (CSTR) model with non-limiting outflow, constant solvent volume and constant reaction temperature. (c) Unilamellar lipid vesicle, with variable internal solvent volume determined by osmotic water flow equalizing the total solute concentration difference across the semi-permeable membrane. (d) Lipid vesicle morphology space, with vesicle viability space drawn as the sub-region of all possible morphologies (grayscale region). Axes express vesicle volume Ω and surface area Sµ as the nm diameter of a sphere having volume Ω or surface area Sµ, respectively. Spherical vesicles (Φ = 1) are located when Ω (in nm)= Sµ (in nm). Circles represent vesicle cross-sections, drawn to scale (8.5% of the axes’ scale). Blue crosses indicate how the morphology of a spherical d = 800 nm giant unilamellar vesicle (GUV) changes, when (i) gaining surface or (ii) losing volume. Both conditions bring the vesicle toward more filamentous or prolate states. Prolate states are depicted as strings of smaller spherical vesicles, only to give an idea of the volume and surface ratio at the {Ω, Sµ} point; the meaning is not that the vesicle has necessarily divided into identical daughters at this stage. Red crosses indicate that the spherical d = 800 nm vesicle will burst by (iii) losing too much surface or, conversely, (iv) gaining too much volume.

Mentions: The traditional and mathematically most simple way to formalize a reaction system held far from equilibrium (FFE) is to assume well-stirred conditions and the existence of a permanent concentration gradient in the form of two (or more) inexhaustible reservoir species (Figure 1a). Under these reservoir conditions, the dynamic behavior of reaction intermediate species is of interest, species which dissipate energy between the high and low energy reservoirs (resource and waste species).  Such a system has a dimension equal to the number of intermediate species only, and each concentration time derivative contains just mass action kinetics (MAK) terms.


Emergent chemical behavior in variable-volume protocells.

Shirt-Ediss B, Solé RV, Ruiz-Mirazo K - Life (Basel) (2015)

Chemical Reactor Models. (a) A chemical reaction held far-from-equilibrium by use of two constant concentration reservoirs (reservoir conditions). (b) Continuous-flow stirred tank reactor (CSTR) model with non-limiting outflow, constant solvent volume and constant reaction temperature. (c) Unilamellar lipid vesicle, with variable internal solvent volume determined by osmotic water flow equalizing the total solute concentration difference across the semi-permeable membrane. (d) Lipid vesicle morphology space, with vesicle viability space drawn as the sub-region of all possible morphologies (grayscale region). Axes express vesicle volume Ω and surface area Sµ as the nm diameter of a sphere having volume Ω or surface area Sµ, respectively. Spherical vesicles (Φ = 1) are located when Ω (in nm)= Sµ (in nm). Circles represent vesicle cross-sections, drawn to scale (8.5% of the axes’ scale). Blue crosses indicate how the morphology of a spherical d = 800 nm giant unilamellar vesicle (GUV) changes, when (i) gaining surface or (ii) losing volume. Both conditions bring the vesicle toward more filamentous or prolate states. Prolate states are depicted as strings of smaller spherical vesicles, only to give an idea of the volume and surface ratio at the {Ω, Sµ} point; the meaning is not that the vesicle has necessarily divided into identical daughters at this stage. Red crosses indicate that the spherical d = 800 nm vesicle will burst by (iii) losing too much surface or, conversely, (iv) gaining too much volume.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4390847&req=5

life-05-00181-f001: Chemical Reactor Models. (a) A chemical reaction held far-from-equilibrium by use of two constant concentration reservoirs (reservoir conditions). (b) Continuous-flow stirred tank reactor (CSTR) model with non-limiting outflow, constant solvent volume and constant reaction temperature. (c) Unilamellar lipid vesicle, with variable internal solvent volume determined by osmotic water flow equalizing the total solute concentration difference across the semi-permeable membrane. (d) Lipid vesicle morphology space, with vesicle viability space drawn as the sub-region of all possible morphologies (grayscale region). Axes express vesicle volume Ω and surface area Sµ as the nm diameter of a sphere having volume Ω or surface area Sµ, respectively. Spherical vesicles (Φ = 1) are located when Ω (in nm)= Sµ (in nm). Circles represent vesicle cross-sections, drawn to scale (8.5% of the axes’ scale). Blue crosses indicate how the morphology of a spherical d = 800 nm giant unilamellar vesicle (GUV) changes, when (i) gaining surface or (ii) losing volume. Both conditions bring the vesicle toward more filamentous or prolate states. Prolate states are depicted as strings of smaller spherical vesicles, only to give an idea of the volume and surface ratio at the {Ω, Sµ} point; the meaning is not that the vesicle has necessarily divided into identical daughters at this stage. Red crosses indicate that the spherical d = 800 nm vesicle will burst by (iii) losing too much surface or, conversely, (iv) gaining too much volume.
Mentions: The traditional and mathematically most simple way to formalize a reaction system held far from equilibrium (FFE) is to assume well-stirred conditions and the existence of a permanent concentration gradient in the form of two (or more) inexhaustible reservoir species (Figure 1a). Under these reservoir conditions, the dynamic behavior of reaction intermediate species is of interest, species which dissipate energy between the high and low energy reservoirs (resource and waste species).  Such a system has a dimension equal to the number of intermediate species only, and each concentration time derivative contains just mass action kinetics (MAK) terms.

Bottom Line: 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.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.Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

View Article: PubMed Central - PubMed

Affiliation: ICREA-Complex Systems Lab, Institut de Biologia Evolutiva, CSIC-UPF, 08003 Barcelona, Spain. ben@shirt-ediss.me.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus