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

2 Photosynthesis Requires chlorophyll as catalyst What about chiralitry?

3 Aminoacids in protein: left-handed Sugars in DNA and RNA: right-handed Louis Pasteur ( ) animogroup carboxylgroup

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

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

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 template-directed oligomerization poly (C D )  oligo (G D )  Mononucleotides with wrong Chirality terminate chain growth cytosine guanine ok poisoned Joyce, et al. (incl. Orgel) (1984) (using HPLC)

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

9 Relevant experiments: crystals Crystal growth with stirring: primary nucleation suppressed Crystal growth, many different nucleation sites: racemic mixture 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 ~2 1-n

15 Coupling to substrate S Q L 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)  Q L = Q R (L n,R n ) Source of L 1 monomers Q L

16 Self-catalytic effect Form of Q L = Q R (L n,R n ) Possible proposals for C L (similarly for C R )

17 Birfurcation properties  Mononucleotides with wrong Chirality terminate chain growth

18 Stability Relative perturbation of racemic solution, 10 -4

19 Conservation law Dependence on fidelity where

20 Differences to Sandars Coupling to substrate: here proportional to E L –in Sandars: [L N ] 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 Propagating front solutions Reaction-diffusion equation Proto type: Fisher’s equation wave speed with Tuomas Multamäki

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

29 RNA itself as enzyme

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

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