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Homochirality: models and results

Homochirality: models and results. Axel Brandenburg, Anja Andersen, Susanne H öfner , Martin Nilsson. To appear in Orig. Life Evol. Biosph., q-bio.BM/0401036. Photosynthesis. Requires chlorophyll as catalyst What about chiralitry?.

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Homochirality: models and results

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  1. Homochirality:models and results Axel Brandenburg, Anja Andersen, Susanne Höfner, Martin Nilsson To appear in Orig. Life Evol. Biosph., q-bio.BM/0401036

  2. Photosynthesis Requires chlorophyll as catalyst What about chiralitry?

  3. Aminoacids in protein: left-handedSugars in DNA and RNA: right-handed carboxyl group animo group Louis Pasteur (1822-1895)

  4. (from lecture of Antoine Weiss) Racemic mixture Racemization dating method

  5. Miller/Urey experiment Wait 1 week 15 organic compounds 2% amino acids (11 different ones) racemic mixture

  6. Chirality and origin of life • Dead stuff not chiral, so is chirality • with racemic mixture: structure fragile • Importance: • Prerequisite of life (provides curvature and twist) • Consequence of life (enzymatic reactions) • Miller-Urey amino acids: both chiralities • in Murchison meteorite: mostly left-handed! • but contamination is debated… • Reasons discussed: circularly polarized light, beta-decay (weak force), homochiral template

  7. Relevant experiments: nucleotides  Mononucleotides with wrong Chirality terminate chain growth ok poisoned template-directed oligomerization poly (CD)  oligo (GD) (using HPLC) guanine cytosine Joyce, et al. (incl. Orgel) (1984)

  8. Contergan: was sold as racemic mixture Cures morning sickness during pregnancy causes misformations (abundaned in December 1961)

  9. Relevant experiments: crystals Crystal growth, many different nucleation sites: racemic mixture Crystal growth with stirring: primary nucleation suppressed Autocatalytic self-amplification? Frank (1953), Goldanskii & Kuzmin (1989), …

  10. Auto-catalytic effect in dead matter Alkanol with 2% e.e. Treated with carboxylaldehyde

  11. Model by Saito & Hyuga (Jan 2004) Bimodal behavior

  12. Model by Sandars (Dec 2003, OLEB) Reaction for left-handed monomers Loss term for each constituent

  13. Combined equations Loss term for each constituent

  14. Including enantiomeric cross-inhibition Loss term for each constituent Racemic solution ~21-n

  15. Coupling to substrate S Source of L1 monomers QL QL comes from substrate acts as a sink of S S sustained by source Q Catalytic properties of substrate (depending on how much L and R one has)  QL = QR(Ln,Rn)

  16. Self-catalytic effect Form of QL = QR(Ln,Rn) Possible proposals for CL(similarly for CR)

  17. Birfurcation properties  Mononucleotides with wrong Chirality terminate chain growth

  18. Stability Relative perturbation of racemic solution, 10-4

  19. Dependence on fidelity Conservation law where

  20. Differences to Sandars • Coupling to substrate: here proportional to EL • in Sandars: [LN] • Outer boundary condition: here open • in Sandars: prescribed damping term • Future extensions: • Chain braking • add spatial 3D dynamics

  21. Reduced equations Quantitatively close to full model

  22. Initial bias Effect in reality very weak

  23. Spatially extended model with Tuomas Multamäki Reaction-diffusion equation Proto type: Fisher’s equation Propagating front solutions wave speed

  24. 1D model (reaction-diffusion equation) Propagation into racemic environment

  25. 2D model (reaction-diffusion equation) Short run

  26. 2D model (reaction-diffusion equation) Time scale longer than for simple fronts

  27. P polymerization olymerization in 1D chain growth, Rn and Ln in different places

  28. Walter Gilbert (1986) The RNA world • Central dogma of chemistry of life • DNA  RNA  protein enzyme • all enzymes are themselves proteins?

  29. RNA itself as enzyme

  30. pre-RNA worlds Many problems: stability of sugars 2-amino ethyl glycin (AEG)

  31. pre-RNA worlds better alternative: Nelson, Levi, Miller (2000) PE Nielsen (1993)

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