Lipidia Lipidia : : AnAn Artificial Artificial Chemistry Chemistry ofof Self-Replicating Self-Replicating
AssembliesAssembliesofof Lipid-likeLipid-like Molecules Molecules
Modeling a ”Lipid World””Lipid World” scenarioof Origin of LifeOrigin of Life
Barak Naveh, Moshe Sipper, Doron Lancet and Barak Shenhav
RNARNA World World ScenarioScenario
RNA molecules can act as catalystscatalysts in addition to acting as templatestemplates.
In theoryIn theory, some molecules might be able to store genetic information and to catalyse their own creation.
Such molecules will become self-replicatorsself-replicators.
In practiceIn practice, could be very difficult, especially in the putative pre-biotic conditions.
Observation: No bio-molecule is known to self-replicate on its ownon its own.
Hypothesis: Self-replication may not have been achieved by a single molecule, but rather by a molecular ensemblemolecular ensemble.
The “Lipid World”“Lipid World” scenario: • assumes self-replication was first achieved by
non-covalent assembliesnon-covalent assemblies of lipid-likelipid-like moleculesthat contained mutually catalytic setsmutually catalytic sets.
A A LipidLipid World World ScenarioScenario
Why Why LipidsLipids??
Likely to have been present
in early earth.
Naturally self-organize into self-organize into
higher level structureshigher level structures.
PrimitivePrimitive GrowthGrowth andand DivisionDivision
assembliesassemblies of lipid-like molecules (amphiphilesamphiphiles).
a primitive form of growth and division.
a process that, though noisy, is capable of self-replicationcapable of self-replication.
reasonable fidelity.
Could Be Useful AsCould Be Useful As
Stable self-replicating micro-environments.
Polymerizers / Reactors.
Surface templating (Rasmussen, 2002)
GA
GA
The The GARD GARD ModelModel
Molecules from the environment
may joinjoin the assembly.
Molecules may leaveleave the
assembly.
Join and Leave rates rates are
enhanced by catalysis, depending
on the compositions of the
assembly and the environment.
Graded Autocatalysis Replication Domain
LipidiaLipidia
Assemblies are colored according to species.
Environment Environment with free molecules.
AssembliesAssemblies ofmolecules recruitedfrom the environment.
Assembly dynamics modeled using GARDGARD model.
GridGrid Dynamics Dynamics
environment
diffusiondiffusionenvironment
diffusiondiffusionassembly
driftdriftassembly
driftdrift
GARDGARD and and LipidiaLipidia
infiniteinfinite environment:
assembly's effect on the environment is not modeled.
food molecules are in infinite supply.
one assembly at a time.
finite finite environmentenvironment for every grid locationgrid location.
based on a 2D gridgrid.
locations may contain zero or more assembliesassemblies of molecules.
many assemblies in parallel.
birth, death, diffusion, and more…
Basic GARDBasic GARD LipidiaLipidia
????
ResultsResults
Infi
nite
Infi
nite
En
viro
nm
en
tEn
viro
nm
en
t
Fin
iteFin
ite E
nviro
nm
en
tEn
viro
nm
en
t
Results Results (summary)(summary)
InfiniteInfinite env. FiniteFinite env.
No. speciesafter 15M reactions 51 135
Time to first
50 species62 8
Results Results (cont.)(cont.)
GARD is validatedvalidated for finite environment.
A finite environmentfinite environment produces more more speciesspecies, and faster faster, than an infinite environment.
A finite environmentfinite environment allows more more assemblies assemblies to occur in more species more species and in greater numbers.
Assembly population diversity increasespopulation diversity increases.
ConclusionsConclusions
One might think: An infinite supply of resources, in the form of “food” molecules, might help to might help to “do more”“do more”.
Our findings show it only helps to helps to “do more of the same”“do more of the same”.
DiversityDiversity seems to spring when resourcesresources are are limitedlimited.