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

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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

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