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Astrobiology, homochirality, and origin of life

Astrobiology, homochirality, and origin of life. Astrobio logy in Nordic countries Role of Nordita Meetings: Copenhagen, Turku, Oslo, Stockholm Winter school last January Our current interests: homochirality and origin of life peptide world, RNA world.

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Astrobiology, homochirality, and origin of life

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  1. Astrobiology, homochirality, and origin of life • Astrobiology in Nordic countries • Role of Nordita • Meetings: Copenhagen, Turku, Oslo, Stockholm • Winter school last January • Our current interests: • homochirality and origin of life • peptide world, RNA world Axel Brandenburg, based on work with Anja Andersen, Martin Nilsson, Susanne Höfner, Tuomas Multamäki, Harry and Kirsi Lehto (Nordita) Int. J. Astrobio. 3, 209 (2004), 4, 75 (2005), Orig. Life Evol. Biosph. 35, 225 (2005), 35, 507 (2005)

  2. Astrophysics: staff and duties Nordita in Copenhagen

  3. Nordita in Stockholm • Expected developments • ~6 new post-docs Nordic+non-Nordic • ~2 new assist. profs • ~5 programs/year • visiting professors (1/2-2yr) • Nordita-days next August

  4. AB-School Jan 2004 Copenhagen Aug 2004 Turku Jan 2005 Copenhagen Nov 2005 Oslo Jan 2006 Kittilä

  5. Topics at Nordic AB meetings Atmospheric escape Martian gullies Icelandic analogues Subglacial lakes Geological evolution Cyanobacteria Deep biosphere Extremophiles Deep biosphere Meteorites stardust RNA world geochemistry Nucleotide Synthesis In space Deep biosph Ancient DNA, PNA, Early life evidence Climate, exoplanets Mars simulator Interstellar chem.

  6. On Earth: Life 3.8 Gyrago Frozen/liquid water on Mars

  7. From dust to planets Exoplanets Water delivery Habitable worlds Archaen world Volcanoes, carbon cycle Impacts, panspermia Greenhouse effect Miller experiment Amino acids, chemistry Artificial life Origin of life RNA world, TNA, PNA homochirality Early life Extremophiles Cyanobacteria Oxygen, methane evol. Astrobiology: The range of problems

  8. Time line First life planetesimals Sun ignites T0=1010 yr after Big Bang All gas gone Remaining dust settles 104 yr 106 yr 108 yr 109 yr

  9. Amino acids in proteins: left-handedSugars in DNA and RNA: right-handed Is chirality: (i) prerequisite (ii) consequence of life? carboxyl group Louis Pasteur (1822-1895) animo group chlorophyll

  10. Producing enantiomeric excess (e.e) • Life only develops in homochiral environment • Homochirality is a prerequisite • However: no mechanism produces 100% e.e. • only minute partial excess possible (electroweak) • slightly bigger for large Z, goes like Z5 Cu (II) ions • Still need amplification mechanism • Frank (1953) model (plus extensions): nucleotides • Autocatalysis and enantiomeric cross inhibition • Plasson, Bersini, Commeyras (2004): peptides

  11. Chirality selection during polymerizationof the first replicating molecule? lipid world? Peptide world, PNA world dual world RNA world achiral RNA DNA proteins RNA chiral Rasmussen et al (2003 Artif. Life9, 269-316) Isotactic polymer (same chirality) R Monomers to dimers “waste” (enantiomeric cross-inhibition) L

  12. RNA and peptide worlds • Polycondensation reactions • Isotractic chains strongly preferred • Self-amplification conceivable • Initially (nonliving): e.e.=0 • During polycondensation: e.e. ~ exp(lt) • l is the growth rate

  13. Activation D  D*, L  L* Polymerization D+D DD, L+L  LL Epimerization DL  LL, LD  DD Depolymerization DD  D+D, LL  L+L Template-directed (PCR-like) Enantiomeric cross-inhibition Autocatalytic production of new mono-nucleotides ( but uncertain) RNA versus peptide worlds peptide world RNA world APED model (Plasson et al.)

  14. Recap of Frank-type model (Frank 1953) auto-catalysis alone kinetic equation exponential growth enantiomeric excess: catalyst

  15. Need mutual antagonism add cross-inhibition kinetic equation unspecific antagonism

  16. Initial bias not necessary • Exponential amplification • Initial excess can be virtually zero • Initial bias may not change this • depends on strength • Second genesis: other chirality? • would be cool • but is not necessary Bifurcation diagram with Andersen, Höfner, Nilsson Orig. Life Evol. Biosph. 35, 225 (2005) fidelity

  17. Relevant experiments: autocatalysis now also: proline-catalyzed reaction (Blackmond 2004) pyrimidine-5-carboxylaldehyde with diisopropylzinc  autocatalytic self-amplification cf. Frank (1953), Goldanskii & Kuzmin (1989), … Soai et al. (1995) • self-amplification + competition important

  18. Relevant experiments: nucleotides  Mononucleotides with wrong chirality terminate chain growth ok poisoned template-directed oligomerization poly (CD)  oligo (GD) (using HPLC)  enantiomeric cross-inhibition guanine cytosine Joyce et al. (1984)

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

  20. Relevant experiments: crystals Crystal growth, many different nucleation sites: racemic mixture Crystal growth with stirring: primary nucleation suppressed Kondepudi et al. (1990)  competition important

  21. APED model (Plasson et al. 2004) a: activation p: polymer. a: inhibition h: depolym. e: epimerization on N-terminal DLLL not DL DD

  22. APED model equations Consider limit of large h and e

  23. APED model equations limit of large h and e corresponding reaction  D catalyzes conversion of both D* and L* into D

  24. APED model equations additional limit of large p corresponding reaction APED model is auto-catalytic after all! subtract

  25. Where could this work? a) hydrothermal vents Braun & Libchaber (2003) b) Tides Lathe (2003)

  26. Early forms of protocells Michael J. Russell (2006, Am. Sci. 94, 32-39)

  27. Spatially extended model with Tuomas Multamäki, Int. J. Astrobio. 3, 209 (2004) Reaction-diffusion equation 1350 1349 Proto type: Fisher’s equation 1348 Propagating front solutions 1347 wave speed Spread of the black death

  28. 1D and 2D models (reaction-diffusion equation) Propagation into racemic environment Disappearence of isolated islands

  29. Piecewise linear increase Reduced equations add/subtract:

  30. Effects of turbulence

  31. Pencil Code • Started in Sept. 2001 with Wolfgang Dobler • High order (6th order in space, 3rd order in time) • Cache & memory efficient • MPI, can run PacxMPI (across countries!) • Maintained/developed by ~20 people (CVS!) • Automatic validation (over night or any time) • Max resolution so far 10243 , 256 procs • Isotropic turbulence • MHD, passive scl, CR • Stratified layers • Convection, radiation • Shearing box • MRI, dust, interstellar • Sphere embedded in box • Fully convective stars • geodynamo • Other applications • Homochirality • Spherical coordinates

  32. Conclusions • Astrobiology: need to be prepared… • Polymerization model: • Based on measurable processes • Reduction to accurate simplified model • Homochirality in space (earth, interstellar, etc) • Timescales 500 Myr; fossil evidence of spatially fragmented homochirality? • Pencil Code: just google for it • Detailed manual, …

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