CIW Astrobiology Workshop'

1
CIW Astrobiology Workshop. October 25,
2004. D.W. Deamer, Biomolecular Engineering,
University of California, Santa Curz
2
Early forms of life Primary questions. Sources
of organic compounds Self-assembly processes and
chiral selection Energy sources Catalysts for
primitive metabolism Catalysts for
polymerization reactions Origin of
information-storing molecules Origin of
translation Approach to problem Combinatorial
chemistry Organic reactions on mineral
surfaces CIW project
3
Why mineral interfaces?
Lifes origin Not on dry land - Liquid water
required.
Not in bulk ocean water - too dilute, at
equilibrium.
Most plausible - mineral-aqueous interface.
But what energy is available to drive synthetic
reactions?
Possible energy source Fluctuating environments
such as intertidal zones, geothermal springs, day
night cycles.
4
(No Transcript)
5
Mineral-aqueous interfaces as organizing
agents Organizing interface - Cairns-Smith,
1980s Montmorillonite clay surfaces - Ferris
lab Activated mononucleotides --gt
RNA Selective surface for chiral enhancement -
Hazen 2002. Chiral calcite surfaces selectively
adsorb L or D aspartic acid Energy source -
Wächtershäuser Pyrite formation can provide
both an organizing surface and a source of free
energy. Iron and chromium minerals catalyze
Fischer-Tropsch type Reactions - Oro et al.
1975 McCollom, Rushdi, Simoneit 2000 Hydrogen
gas carbon dioxide --gt hydrocarbons
6
Kamchatka volcanic sites are mineral-aqueous
hydrothermal systems. High altitude, high
latitude, recent eruption (1961) Minimal
biological/human contributions to
organics Russian reports of organics in vent gas
mixtures Alkanes and alkenes C4 - C12 normal
and branched chain isomers Aromatics benzene,
toluene, xylene and derivatives Ketone,
alcohols, ethers, esters Chlorofluorocarbons
CFCl3, CF2Cl2. CHCl3, CCl4
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
.But if (and oh, what a big if) we find a warm
little pond, with ammonium and phosphate
salts. C. Darwin, in a letter to Hooker,
1870 Can we model a warm little pond? Or what
about a hot little puddle in Kamchatka?
17
(No Transcript)
18
Experiment The hot little puddle contains 7
liters of boiling water contained in a clay
basin. Add 4 amino acids (gly, ala, val, asp) 1
g each Add 4 nucleobases (AUGC) 1 g each Add
phosphate (2g) glycerol (2 g) myristic acid
(2g) Sample over time intervals of minutes to
days Questions How fast do the organics
degrade? Does any synthetic chemistry occur?
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
Preliminary results from TLC analysis Uracil
disappears in a few minutes - degraded? Phosphate
is lost in a few minutes apatite? Amino acids
are largely absent after 2 hours A ninhydrin
positive spot is still present after 9
days Fatty acid is still present after 9 days.
23
Significance?
In high temperature-high pressure geochemical
environments, mineral surfaces may catalyze the
synthesis of biologically relevant compounds from
reactants such as CO2, NH3 In the presence of a
specific mineral surface, a mixture of plausible
organic monomers assembles on the surface
and spontaneously produces a novel polymer. The
polymer has the potential for catalytic capacity,
energy capture, and information storage. The
polymer has properties that suggest how it could
serve as a transient scaffold leading to an RNA
world.
24
The unit of all life today is the cell. Cells
can be defined as membrane-bounded systems of
replicating, catalytic polymers that use
nutrients and energy to grow and
reproduce. Question How did cellular life
begin? All cells today have membranous
boundaries. What was the origin of membranes?
25
SOURCES OF AMPHIPHILES? Photochemical synthesis
in ISM Dworkin et al. 2001 Delivery to planetary
surfaces during accretion Oro, 1961 Delsemme,
1967 Chyba and Sagan, 1992 Bar-Nun,
2002 Geochemical synthesis McCollum et al. 1999
Rushdi et al 2001
26
Amphiphilic molecules are synthesized under
simulated geochemical conditions. Fischer-Tropsch
type (FTT) synthesis Reactants carbon
monoxide, hydrogen gas Catalyst iron Conditions
High pressure, high temperature (gt250C) Products
hydrocarbons, long chain alcohols and acids
27
McCollom et al. 1999
Decanol
Nonanoic acid
28
DECANOATE-DECANOL VESICLES
29
dsDNA (600 BP) IN DECANOIC ACID VESICLES
30
Can cellular life begin in a hot little puddle?
Or a marine hydrothermal site? Facing up to the
biophysical facts of life. Osmotic effects -
solute gradients across membranes can collapse or
burst vesicles. Divalent cations (calcium,
magnesium, iron) cause aggregation of
amphiphiles. Higher temperature ranges cause
instability in bilayer structures.
31
Disruptive to self-assembly processes Hot
submarine hydrothermal vents Osmotic effects on
vesicles, precipitation of amphiphiles by
divalent cations, elevated temperatures - all
inhibit stability of self-assembled structures.
Perhaps life did not originate in a marine
environment? Conducive to self-assembly
processes Intermediate temperature ranges, low
ionic solute concentrations. Mineral
stabilization? Monnard et al. Astrobiology
2002.
32
Looking to the future An artificial laboratory
version of cellular life. Pohorille and Deamer,
2001 Szostak et al. 2001 1. Encapsulated
polymerase and template. 2. Inward transport of
nutrient substrates. 3. Energy source to drive
polymerization. 4. Replication of polymerase and
template. 5. Growth/division of membrane
boundary. 6. Regulatory feedback mechanism.