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

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tEn

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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.

Barak Naveh, Moshe Sipper

Dept. of Computer Science, Ben-Gurion University, Israel

Doron Lancet, Barak Shenhav

Dept. Molecular Genetics and the Crown Human Genome Center,Weizmann Institute of Science, Israel

http://ool.weizmann.ac.il/lipidia