Lipidia : An Artificial Chemistry of Self-Replicating Assemblies of Lipid-like Molecules

1. Lipidia : An Artificial Chemistry of Self-Replicating AssembliesofLipid-like Molecules Modeling a ”Lipid World” scenario of Origin of Life Barak Naveh, Moshe Sipper, Doron Lancet and Barak Shenhav

2. RNA World Scenario • RNA molecules can act as catalysts in addition to acting as templates. • In theory, some molecules might be able to store genetic information andto catalyse their own creation. • Such molecules will become self-replicators. • In practice, could be very difficult, especially in the putative pre-biotic conditions.

3. A Lipid World Scenario • Observation: No bio-molecule is known to self-replicate on its own. • Hypothesis: Self-replication may not have been achieved by a single molecule, but rather by a molecular ensemble. • The “Lipid World” scenario: • assumes self-replication was first achieved bynon-covalent assemblies of lipid-like moleculesthat contained mutually catalytic sets.

4. Why Lipids? • Likely to have been present in early earth. • Naturally self-organize into higher level structures.

5. PrimitiveGrowthandDivision • assemblies of lipid-like molecules (amphiphiles). • a primitive form of growth and division. • a process that, though noisy, is capable of self-replication. • reasonable fidelity.

6. G A A G Could Be Useful As • Stable self-replicating micro-environments. • Polymerizers / Reactors. • Surface templating (Rasmussen, 2002)

7. Molecules from the environment may join the assembly. Molecules may leave the assembly. Join and Leave rates are enhanced by catalysis, depending on the compositions of the assembly and the environment. The GARD Model Graded Autocatalysis Replication Domain

8. Environment with free molecules. Assemblies of molecules recruited from the environment. Assembly dynamics modeled using GARDmodel. Lipidia Assemblies are colored according to species.

9. Grid Dynamics assembly drift environment diffusion

10. infinite environment: assembly's effect on the environment is not modeled. food molecules are in infinite supply. one assembly at a time. finite environment for every grid location. based on a 2Dgrid. locations may contain zero or more assemblies of molecules. many assemblies in parallel. birth, death, diffusion, and more… GARDand Lipidia Basic GARD Lipidia ?

11. Results InfiniteEnvironment FiniteEnvironment

12. Results (summary)

13. Results (cont.) • GARD is validated for finite environment. • A finite environment produces more species, and faster, than an infinite environment. • A finite environment allows more assemblies to occur in more species and in greater numbers. • Assembly population diversity increases.

14. Conclusions • One might think: An infinite supply of resources, in the form of “food” molecules, might help to “do more”. • Our findings show it only helps to “do more of the same”. • Diversity seems to spring when resourcesare limited.

15. 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