Astrobiology, homochirality, and origins of life Int. J. Astrobio. 3, 209 (2004), 4, 75 (2005), Orig. Life Evol. Biosph. 35, 225 (2005), 35, 507 (2005) Astrobiology 7, 725 (2007) The four corner stones of astrobiology Astrobiology in Nordic countries Role of Nordita Our current interests: homochirality and origin of life peptide world, RNA world Pencil Code Community effort Suitable for distributed systems

2 Topics at Nordic AB meetings Martian gullies Icelandic analogues Subglacial lakes Mars simulator Interstellar chem. Ancient DNA, PNA, Early life evidence Climate, exoplanets Atmosphericescape Geologicalevolution Extremophiles Deep biosphere Cyanobacteria NucleotideSynthesis In space Meteoritesstardust RNA world Geochemistryastrochemistry Deepbiosph

3 Urey-Miller experiment (1953) 15 organic compounds 2% amino acids (11 different ones) Wait 1 week Reduced gases: H 2, NH 3, CH 4, CO Result: NH 2 -CH 2 -COOH, etc

From exoplanets to extremophiles Radial vel. TransitsDirectmicrolensing

On Earth: Life 3.8 Gyr ago Frozen/liquid water on Mars Carbonic and organic carbon, CaCO 3 versus (CH 2 O) n

6 Time line 10 4 yr 10 6 yr 10 8 yr 10 9 yr planetesimals Sun ignites All gas gone Remaining dust settles First life T 0 =10 10 yr after Big Bang

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

8 Onset of life There is no good definition of life –replication (birth/death), evolution, metabolism –Protolife (simplistic): 2H 2 +CO 2  (CH 2 O)+H 2 O –Ignores waste produced: CH 4, H 3 C-COOH, or O 2 –Ignores replication machinery Hypothesis: primitive life is unavoidable –Several independent geneses of life on early Earth? –No serious competitors to carbon-based life

Aminoacids in proteins: left-handed Sugars in DNA and RNA: right-handed Louis Pasteur ( ) animogroup carboxylgroup chlorophyll Is chirality: (i) prerequisite (ii) consequence of life?

10 Racemic mixture (from lecture of Antoine Weiss) Racemization  dating method  

11 Origins of Homochirality

12 Origin of life ~ origin of homochirality Life requires homochirality –wrong enantiomer: stops polymerization –right and left do not cooperate Dead cells racemize Also: protolife may produce chirality –encymatic reactions keep system from equilibrium –as a result of polymerization But: prebiotic soup was racemic!

13 Producing enantiomeric excess (e.e.) Life only develops in homochiral environment –Homochirality is then a prerequisite However: no mechanism produces 100% e.e. –only minute partial excess possible (electroweak) –slightly bigger for large Z, goes like Z 5  Cu (II) ions Still need amplification mechanism –Frank (1953) model (plus extensions): nucleotides –Autocatalysis and enantiomeric cross inhibition –Plasson, Bersini, Commeyras (2004): peptides

14 Chirality selection during polymerization of the first replicating molecule? R L Isotactic polymer (same chirality) “waste” (enantiomeric cross-inhibition) dual world RNA world PNA world lipid world RNA RNADNA proteins Rasmussen et al (2003 Artif. Life 9, ) achiral chiral Polymerization

15 Exponential amplification recap of Frank-type model (Frank 1953) auto-catalysis alone kinetic equation enantiomeric excess: exponentialgrowth catalyst

16 Need also mutual antagonism (to siphon off the bad guys) add cross-inhibition kinetic equation unspecific antagonism

17 Prebiotic experiments: nucleotides poly (C D )  oligo (G D )  Mononucleotides with wrong chirality terminate chain growth cytosine guanine ok poisoned Joyce et al. (1984) (HPLC) template-directed polymerization ~polymerase chain reaction (PCR) Serious difficulty: requires building blocks of the same chirality

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

19 Steps toward realism (i)Consider polymerization of nucleotides i.e. homochirality developed during RNA world autocatalysis requires longish polymers (ii)Peptide world (new mechanism) no explicit autocatalysis required appears chemically feasible (iii)Spatially extended systems independent origins at different locations on Earth

20 (i) Polymerization model of Sandars Reaction for left-handed monomers Loss term for each constituent Orig. Life Evol. Biosph. 33, (2003)

21 3 different classes of mechanisms (i)Autocatalysis and mutual antagonism- - Frank (1953) model - Grow both, and dump pairs - Has been applied to RNA world (ii) crystal growth with stirring - larger crystals spawn more nucelation sites (iii) constructive autocatalysis (see below) - has been applied to peptides

22 (ii) RNA versus peptide worlds 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 stability… RNA world peptide world APED model (Plasson et al.)

23 Net reactions

24 Reduced APED model a one way round-about For nearly racemic state:

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

26 1D reduced model (reaction-diffusion equation) Propagation into racemic environment

27 2D model (reaction-diffusion equation) X (X-Y)[1-(X-Y) 2  X-Y   ]

28 Piecewise linear increase

29 Piecewise linear increase add/subtract: Reduced equations

30 Initial e.e. not related to final e.e.

31 3-D and effects of turbulence

32 Where could this work? Braun & Libchaber (2003) a) hydrothermal vents b) Deep biosphere Michael J. Russell (2006, Am. Sci. 94, 32-39) ideas about first Protocells

Pencil Code Started in Sept with Wolfgang Dobler High order (6 th order in space, 3 rd order in time) Cache & memory efficient MPI, can run PacxMPI (across countries!) Maintained/developed by ~40 people (SVN) Automatic validation (over night or any time) Max resolution so far , 4096 procs Isotropic turbulence – –MHD, passive scl, CR Stratified layers – –Convection, radiation Shearing box – –MRI, dust, interstellar – –Self-gravity Sphere embedded in box – –Fully convective stars – –geodynamo Other applications – –Homochirality – –Spherical coordinates

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36 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, …