homochirality: models and results
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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?. - PowerPoint PPT PresentationTRANSCRIPT
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Homochirality:Homochirality:models and resultsmodels and results
Axel Brandenburg, Anja Andersen, Axel Brandenburg, Anja Andersen, Susanne HSusanne Höfneröfner, Martin Nilsson, Martin Nilsson
To appear in Orig. Life Evol. Biosph., q-bio.BM/0401036To appear in Orig. Life Evol. Biosph., q-bio.BM/0401036
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PhotosynthesisPhotosynthesisRequires chlorophyllRequires chlorophyll
as catalystas catalystWhat about chiralitry?What about chiralitry?
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Aminoacids in protein: left-handedAminoacids in protein: left-handedSugars in DNA and RNA: right-handedSugars in DNA and RNA: right-handed
Louis PasteurLouis Pasteur(1822-1895)(1822-1895)
animoanimogroupgroup
carboxylcarboxylgroupgroup
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Racemic mixtureRacemic mixture(from lecture of(from lecture ofAntoine Weiss)Antoine Weiss)
RacemizationRacemizationdating methoddating method
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Miller/Urey experimentMiller/Urey experiment
15 organic compounds15 organic compounds2% amino acids (11 different ones)2% amino acids (11 different ones)
racemic mixtureracemic mixture
Wait 1 weekWait 1 week
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Chirality and origin of lifeChirality 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
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Relevant experiments: nucleotidesRelevant experiments: nucleotides
template-directed oligomerizationtemplate-directed oligomerizationpoly (Cpoly (CDD) ) oligo (G oligo (GDD))
Mononucleotides with wrongMononucleotides with wrongChirality terminate chain growthChirality terminate chain growth
cytosinecytosine guanineguanine
okok
poisonedpoisoned
Joyce, et al. (incl. Orgel) (1984)Joyce, et al. (incl. Orgel) (1984)
(using HPLC)(using HPLC)
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Contergan: was sold as racemic mixtureContergan: was sold as racemic mixture
causes misformationscauses misformations Cures morning sicknessCures morning sicknessduring pregnancyduring pregnancy
(abundaned in December 1961)(abundaned in December 1961)
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Relevant experiments: crystalsRelevant experiments: crystals
Crystal growth with stirring:Crystal growth with stirring:primary nucleation suppressedprimary nucleation suppressed
Crystal growth, many differentCrystal growth, many differentnucleation sites: racemic mixturenucleation sites: racemic mixture
Autocatalytic self-amplification?Autocatalytic self-amplification?Frank (1953), Goldanskii & Kuzmin (1989), …Frank (1953), Goldanskii & Kuzmin (1989), …
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Auto-catalytic effect in dead matterAuto-catalytic effect in dead matter
Alkanol with 2% e.e.Alkanol with 2% e.e.Treated withTreated with
carboxylaldehydecarboxylaldehyde
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Model by Saito & Hyuga (Jan 2004) Model by Saito & Hyuga (Jan 2004)
Bimodal behaviorBimodal behavior
ssrksdt
ds
rsrkrdt
dr
)1(
)1(
2
2
)1(
)1(
srkdt
ds
srkdt
dr
s
r
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Model by Sandars (Dec 2003, OLEB) Model by Sandars (Dec 2003, OLEB)
]][[2][ 11
211
LLkLdt
d
LLL
nSn
nk
nS
]][[2][
]][[2][
111
111
LLkLdt
d
LLkLdt
d
nS
nSn
Reaction for left-handed monomersReaction for left-handed monomers
Loss term for each constituentLoss term for each constituent
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Combined equationsCombined equations
N
nnS
nnSn
LLkLdt
d
LLLkLdt
d
111
11
][][2][
][][][2][
Loss term for each constituentLoss term for each constituent
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Including enantiomeric cross-inhibitionIncluding enantiomeric cross-inhibition
N
nnS
nnIn
RLRkRdt
d
RLRLRkRLdt
d
1111
11111
][][2][
][][][2...][
Loss term for each constituentLoss term for each constituent
]][[2][ 11
12
1
RLkRLdt
d
RLRL
nIn
nk
nI
Racemic solution ~2Racemic solution ~21-n1-n
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Coupling to substrate Coupling to substrate SS
QQL L comes from substratecomes from substrate
acts as a sink of acts as a sink of SSSS sustained by source sustained by source QQ
)(][ RL QQQSdt
d
Catalytic properties of substrateCatalytic properties of substrate(depending on how much (depending on how much LL and and RR one has) one has)
QQLL = = QQRR((LLnn,R,Rnn) )
N
nnSL LLkQL
dt
d
111 ][][2][
Source of LSource of L11 monomers monomers QQLL
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Self-catalytic effectSelf-catalytic effect
Form of Form of QQLL = = QQRR((LLnn,R,Rnn) )
LRCR
RLCL
CfCfSkQ
CfCfSkQ
11][
11][
21
21
21
21
(our work)][
2004)Coveney & (Wattis][
y)possibilit(another ][
2003) (Sandars][
n
n
M
N
L
Ln
L
L
L
C
Possible proposals for Possible proposals for CCLL (similarly for (similarly for CCRR))
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Birfurcation properties Birfurcation properties
Mononucleotides with wrongMononucleotides with wrongChirality terminate chain growthChirality terminate chain growth
1/ SI kk
1.0/ SI kk
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StabilityStability
Relative perturbation ofRelative perturbation ofracemic solution, 10racemic solution, 10-4-4
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Conservation Conservation lawlaw
N
nnL LnE
1
][
][][1 11
1 RRLnEN
nnLR
termssurf. QEEdt
dLRLR
Dependence on fidelityDependence on fidelity
wherewhere
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Differences to SandarsDifferences 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
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Reduced equationsReduced equations
Quantitatively close to full modelQuantitatively close to full model
ryryy
rxrxx
22
22
~/
~/
yxr
yxr
~ 222
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Initial biasInitial bias
Effect in reality very weakEffect in reality very weak
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Spatially extended modelSpatially extended model
Propagating front solutionsPropagating front solutions
Reaction-diffusion equationReaction-diffusion equation
YrYrYY
XrXrXX222
222
~/
~/
Proto type: Fisher’s equationProto type: Fisher’s equation
'')1( XXXX
)( ctxfX 2cwave speedwave speed
wwith Tuomas Multamith Tuomas Multamääkiki
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1D model (reaction-diffusion equation)1D model (reaction-diffusion equation)
Propagation into racemic environmentPropagation into racemic environment
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2D model (reaction-diffusion equation)2D model (reaction-diffusion equation)
Short runShort run
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2D model (reaction-diffusion equation)2D model (reaction-diffusion equation)
Time scale longer than for simple frontsTime scale longer than for simple fronts
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P polymerization olymerization in 1DP polymerization olymerization in 1D
chain growth, Rn and Ln in different placeschain growth, Rn and Ln in different places
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The RNA worldThe RNA world
• Central dogma of chemistry of life– DNA RNA protein
enzyme
• all enzymes are themselves proteins?
Walter GilbertWalter Gilbert(1986)(1986)
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RNA itself as enzymeRNA itself as enzyme
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pre-RNA worldspre-RNA worldsMany problems: stability of sugarsMany problems: stability of sugars
2-amino ethyl glycin2-amino ethyl glycin(AEG)(AEG)
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pre-RNA worldspre-RNA worlds
PE Nielsen (1993)PE Nielsen (1993)
better alternative: Nelson, Levi, Miller (2000)better alternative: Nelson, Levi, Miller (2000)