Astrobiology, homochirality, and origin of life

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Astrobiology, homochirality, and origin of life

• Axel Brandenburg, based on work with Anja
  Andersen, Martin Nilsson, Susanne Höfner, Tuomas
  Multamäki, Harry and Kirsi Lehto (Nordita)

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
Int. J. Astrobio. 3, 209 (2004), 4, 75
(2005), Orig. Life Evol. Biosph. 35, 225 (2005),
35, 507 (2005)
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Astrophysics staff and duties
Nordita in Copenhagen
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Nordita in Stockholm

• Expected developments
• 6 new post-docs Nordicnon-Nordic
• 2 new assist. profs
• 5 programs/year
• visiting professors (1/2-2yr)
• Nordita-days next August

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AB-School
Jan 2004 Copenhagen Aug 2004 Turku Jan 2005
Copenhagen Nov 2005 Oslo Jan 2006 Kittilä
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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.
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On Earth Life 3.8 Gyrago
Frozen/liquid water on Mars
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Astrobiology The range of problems

• 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.

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Time line

• 104 yr 106 yr 108 yr 109
  yr

First life
planetesimals
Sun ignites
T01010 yr after Big Bang
All gas gone Remaining dust settles
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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
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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

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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. Life 9, 269-316)
Isotactic polymer (same chirality)
R
Monomers to dimers
waste (enantiomeric cross-inhibition)
L
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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

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RNA versus peptide worlds
peptide world
RNA world

• Activation D ? D, L ? L
• Polymerization DD? DD, LL ? LL
• Epimerization DL ? LL, LD ? DD
• Depolymerization DD ? DD, LL ? LL

• Template-directed (PCR-like)
• Enantiomeric cross-inhibition
• Autocatalytic production of new mono-nucleotides
  (? but uncertain)

APED model (Plasson et al.)
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Recap of Frank-type model (Frank 1953)
auto-catalysis alone
kinetic equation
exponential growth
enantiomeric excess
catalyst
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Need mutual antagonism
add cross-inhibition
kinetic equation
unspecific antagonism
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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
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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

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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)
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Contergan was sold as racemic mixture
Cures morning sickness during pregnancy
causes misformations
(abandoned in December 1961)
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Relevant experiments crystals
Crystal growth, many different nucleation sites
racemic mixture
Crystal growth with stirring primary nucleation
suppressed
Kondepudi et al. (1990)
? competition important
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APED model (Plasson et al. 2004)
a activation p polymer. a inhibition h
depolym.
e epimerization on N-terminal DL?LL not DL? DD
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APED model equations
Consider limit of large h and e
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APED model equations
limit of large h and e
corresponding reaction
? D catalyzes conversion of both D and L into D
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APED model equations
additional limit of large p
corresponding reaction
?APED model is auto-catalytic after all!
subtract
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Where could this work?
a) hydrothermal vents
Braun Libchaber (2003)
b) Tides
Lathe (2003)
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Early forms of protocells
Michael J. Russell (2006, Am. Sci. 94, 32-39)
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Spatially extended model
with Tuomas Multamäki, Int. J. Astrobio. 3, 209
(2004)
Reaction-diffusion equation
1350
1349
Proto type Fishers equation
1348
Propagating front solutions
1347
wave speed
Spread of the black death
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1D and 2D models (reaction-diffusion equation)
Propagation into racemic environment
Disappearence of isolated islands
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Piecewise linear increase
Reduced equations
add/subtract
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Effects of turbulence
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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

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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,