topics in astrobiology 1.what is and can be done 2. the problem of chirality
TRANSCRIPT
Topics in Topics in AstrobiologyAstrobiology
1.1. What is and can be doneWhat is and can be done
2.2. The problem of chiralityThe problem of chirality
2
The range of problemsThe range of problems
• From dust to planets– Exoplanets
– Water delivery
– Habitable worlds
• Archaen world– Volcanos, Carbon cycle
– Impacts, panspermia
• Miller experiment– Amino acids, chemistry
• Artificial life• Origin of life
– RNA world, TNA, PNA
– homochirality
• Early life– Extremophiles
– cyanobacteria
3
Rough time lineRough time line
104 yr 106 yr 108 yr 109 yr
planetesimalsplanetesimals
Sun ignitesSun ignites
All gas goneAll gas goneRemaining dust settlesRemaining dust settles
First lifeFirst life
4
Time line (later)Time line (later)
5
Carbon cycleCarbon cycle Source of the atmosphereSource of the atmosphere
Venus, Earth:Venus, Earth:active volcanos:active volcanos:thick atmosphthick atmosph..
Mars:Mars:VolcanosVolcanos
extinctextinct
6
Water Water deliverydelivery
via via cometscomets
Comet Comet LINEAR:LINEAR:
same HDOsame HDOratio as onratio as on
Earth’s oceansEarth’s oceans
cf. Hale-Boppcf. Hale-Bopp(too much)(too much)
7
EvaporationEvaporationof LINEARof LINEAR
during fly-by.during fly-by.Cloud ofCloud ofhydrogenhydrogen
Estimated Estimated water content water content
3x103x1099 kg kg(outgassed (outgassed
during fly-by)during fly-by)
Obsered in Ly Obsered in Ly
8
Miller/Urey experimentMiller/Urey experiment
15 organic compounds15 organic compounds2% amino acids (11 different ones)2% amino acids (11 different ones)
Wait 1 weekWait 1 week
9
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)
10
RNA itself as enzymeRNA itself as enzyme
11
pre-RNA worldspre-RNA worldsMany problems: stability of sugarsMany problems: stability of sugars
2-amino ethyl glycin2-amino ethyl glycin(AEG)(AEG)
12
pre-RNA worldspre-RNA worlds
PE Nielsen (1993)PE Nielsen (1993)
better alternative: Nelson, Levi, Miller (2000)better alternative: Nelson, Levi, Miller (2000)
13
PhotosynthesisPhotosynthesis
Requires chlorophyllRequires chlorophyllAs catalystAs catalyst
What about chiralitry?What about chiralitry?
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 OLEB, q-bio.BM/0401036To appear in OLEB, q-bio.BM/0401036
15
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
16
Racemic mixtureRacemic mixture(from lecture of(from lecture ofAntoine Weiss)Antoine Weiss)
RacemizationRacemizationdating methoddating method
17
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
18
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)
19
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)
20
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), …
21
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
22
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
23
Combined equationsCombined equations
N
nnS
nnSn
LLkLdt
d
LLLkLdt
d
111
11
][][2][
][][][2][
Loss term for each constituentLoss term for each constituent
24
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
25
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
26
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))
27
Birfurcation properties Birfurcation properties
Mononucleotides with wrongMononucleotides with wrongChirality terminate chain growthChirality terminate chain growth
1/ SI kk
1.0/ SI kk
28
StabilityStability
Relative perturbation ofRelative perturbation ofracemic solution, 10racemic solution, 10-4-4
29
Conservation Conservation lawlaw
N
nnL LnE
1
][
][][1 11
1 RRLnEN
nnLR
termssurf. QEEdt
dLRLR
Dependence on fidelityDependence on fidelity
wherewhere
30
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
31
Reduced equationsReduced equations
Quantitatively close to full modelQuantitatively close to full model
ryryy
rxrxx
22
22
~/
~/
32
Initial biasInitial bias
Effect in reality very weakEffect in reality very weak
33
ConclusionsConclusions
• There are many astrobiology topics where astrophysicists can help out with their knowledge, as well as technical and computational tools
• Homochirality is a hot one with several papers this topic in each issue of OLEB