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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

Homochirality:models and results

Axel Brandenburg, Anja Andersen, Susanne Höfner, Martin Nilsson

To appear in Orig. Life Evol. Biosph., q-bio.BM/0401036


Photosynthesis
Photosynthesis

Requires chlorophyll

as catalyst

What about chiralitry?


Aminoacids in protein left handed sugars in dna and rna right handed
Aminoacids in protein: left-handedSugars in DNA and RNA: right-handed

carboxyl

group

animo

group

Louis Pasteur

(1822-1895)


Racemic mixture

(from lecture of

Antoine Weiss)

Racemic mixture

Racemization

dating method


Miller urey experiment
Miller/Urey experiment

Wait 1 week

15 organic compounds

2% amino acids (11 different ones)

racemic mixture


Chirality and origin of life
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


Relevant experiments nucleotides
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)


Contergan was sold as racemic mixture
Contergan: was sold as racemic mixture

Cures morning sickness

during pregnancy

causes misformations

(abundaned in December 1961)


Relevant experiments crystals
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), …


Auto catalytic effect in dead matter
Auto-catalytic effect in dead matter

Alkanol with 2% e.e.

Treated with

carboxylaldehyde



Model by sandars dec 2003 oleb
Model by Sandars (Dec 2003, OLEB)

Reaction for left-handed monomers

Loss term for each constituent


Combined equations
Combined equations

Loss term for each constituent


Including enantiomeric cross inhibition
Including enantiomeric cross-inhibition

Loss term for each constituent

Racemic solution ~21-n


Coupling to substrate s
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)


Self catalytic effect
Self-catalytic effect

Form of QL = QR(Ln,Rn)

Possible proposals for CL(similarly for CR)


Birfurcation properties
Birfurcation properties

 Mononucleotides with wrong

Chirality terminate chain growth


Stability
Stability

Relative perturbation of

racemic solution, 10-4


Conservation law

Dependence on fidelity

Conservation law

where


Differences to sandars
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


Reduced equations
Reduced equations

Quantitatively close to full model


Initial bias
Initial bias

Effect in reality very weak


Spatially extended model
Spatially extended model

with Tuomas Multamäki

Reaction-diffusion equation

Proto type: Fisher’s equation

Propagating front solutions

wave speed


1d model reaction diffusion equation
1D model (reaction-diffusion equation)

Propagation into racemic environment



2d model reaction diffusion equation1
2D model (reaction-diffusion equation)

Time scale longer than for simple fronts


P polymerization olymerization in 1d
P polymerization olymerization in 1D

chain growth, Rn and Ln in different places


The rna world

Walter Gilbert

(1986)

The RNA world

  • Central dogma of chemistry of life

    • DNA  RNA  protein

      enzyme

  • all enzymes are themselves proteins?



Pre rna worlds
pre-RNA worlds

Many problems: stability of sugars

2-amino ethyl glycin

(AEG)


Pre rna worlds1
pre-RNA worlds

better alternative: Nelson, Levi, Miller (2000)

PE Nielsen (1993)


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