Transcript 1/23/2013 Dr. Vann: Origins of Life

Origins and Early Evolution
of Life
Richard Vann
CBI 206/ANESTH 445
Physiology and Medicine of Extreme Environments
Spring 2013
1
Origin of Life Topics
• Who, when, what, where, how, why
• Discussion
2
Panspermia &
Spontaneous Generation
Anaximander
611-547 BC
Anaxagoras
500?-428 BC
Aristotle
384-322 BC
•Panspermia: life exists throughout the universe
•Spontaneous generation: life forms by the action
of the sun on the primordial terrestrial slime
3
Recipe for Mice:
Jan Baptista van Helmont (1580-1644)
• Put a soiled shirt and grains of
wheat in a jar and let them
ferment
• Mice form after 21 days
• No experimental evidence
provided
4
Friedrich Wöhler & Urea (1828)
• Organic and non-living compounds are different
(“élan vital, life force, will-to-live”)
• Wöhler made urea by heating
ammonium cyanate
• "I can no longer, so to speak, hold
my chemical water and must tell
you that I can make urea without
needing a kidney, whether of
man or dog."
• A founder of organic chemistry
5
Death of Spontaneous Generation:
Louis Pasteur (1859)
• Living systems arise biotically from other living systems
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Charles Darwin (1871)
“But if (& oh what a big if) we
could conceive in some warm
little pond with all sorts of
ammonia & phosphoric salts, light, heat, electricity, etc.
present, that a protein
compound was chemically
formed, ready to undergo still
more complex changes …”
- letter to Joseph Hooker7
Aleksandr Oparin (1924)
•Early atmosphere was strongly
reducing
•CH4, NH3, H2O , H2 (no O2)
•Sunlight reacted with non-living
chemicals in the “primeval soup”
•Unique, abiogenic, spontaneous
generation of life
•No difference between a living
organism and lifeless matter
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J.B.S. Haldane (1929)
“When ultra-violet light acts on a
mixture of water, carbon dioxide and
ammonia, a vast variety of organic
substances are made, including
sugars and apparently some of the
materials from which proteins are
built up … [B]efore the origin of life
they must have accumulated till the
primitive oceans reached the
consistency of hot dilute soup.”
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Harold Urey
1893-1981
Stanley Miller
1930-2007
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Miller-Urey Ocean-Atmosphere (1953)
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Miller (1953). Production of amino acids under
possible primitive Earth conditions. Science 117: 528.
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Space
• Radio astronomy found evidence of organic
molecules on space dust
• Laboratory simulations of deep space created
organic molecules
• Collisions of comets with primitive Earth
• Murchison meteorite in Australia 1969
contained organic molecules
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Exogenesis and Mars
• Mars may have been habitable a
billion years before Earth
• A meteorite from Mars recovered
in 1984 was claimed to contain
fossil life but this is disputed
• The question of exogenesis from
Mars to Earth is unresolved 14
Hydrothermal Volcanic Vents
DSV Alvin (1977)
Giant Clams
Hydrothermal vents
Tube Worms
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Corliss, Baross & Hoffman. 1981. An hypothesis concerning
the relationship between submarine hot springs and the
origin of life on Earth. Oceanolgica Acta 4 (Suppl): 59-69.
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Deep, Hot Biosphere
Yellowstone (1966)
Rock-Eating Bacteria
Thermophiles
Laboratory Simulations
• Reactants: N2, CO2, S, Fe
• Minerals: Fe-S, Ni-S
• Products: NH3, amino acids,
peptide bonds, C-fixation Fecomplexes
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Origin of Primordial Molecules
- Deamer (2002)
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Timeline
~13.7 bya
~11.5
~4.6
~4.4
~4.4-3.9
~4.2-4.0
4.0-3.7
~3.5
~0.5
~1 mya
“Big Bang” (atomic evolution)
Supernovae & heavy elements
Sun, solar system & Earth
Oceans formed
Chemical evolution
Earliest life at hydrothermal vents?
Earliest life at sea level?
Earliest fossils (Apex chert, WestAus)
Organic evolution (‘naked genes’)
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Social evolution (humans)
When was Earth Ready for Life?
- Schopf (2002)
Sterilizing Meteor Storms
Origin of
Sustained Life
Oldest Fossils:
Stromatolites
Success
of Life
4.5
Planetary
Birth
4.0 3.9
3.5
Billions of Years Ago (bya)
3.0
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Life and the Atmosphere
STERILIZING
METEOR STORMS
CHEMICAL
EVOLUTION
OXYGEN
CATASTROPHE
SUSTAINED
LIFE
OLDEST FOSSILS:
STROMATOLITES
EUKARYOTES
O2
metab
BIF
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3.9 – 3.5 bya
Time
Many
early
life
forms
(temperature, O2 Catastrophe
anaerobic,
radiation,
arsenic,
salt)
LUCA
Present
Biochemistry
(ATP,
Krebs cycle,
RNA, DNA)
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NASA Definition of Life
• “A self-sustaining chemical system
capable of Darwinian evolution”
–Self-sustaining (energy production)
–Chemical system (cell membranes)
–Darwinian evolution (replication)
• What’s the driving force that makes
this system run?
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Energy and Complexity
- Chaisson (2001)
Stars
Planets
Large animals
Human brain
Society
2 erg/g/sec
75
20,000
74,000
500,000
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Sagaminopteron Ornatum
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Thermodynamics
• 1st Law: energy is conserved, not created or
destroyed
– all forms of energy are inter-convertible
• 2nd Law: heat flows from higher to lower temp
– Energy conversions are never complete
• Some energy is always lost to the environment as wasted
heat (ΔQ)
– Entropy (S) = wasted heat divided by the
environmental temperature (ΔS=ΔQ/T)
• Entropy is generated with each energy conversion
• The entropy of a closed system always increases
• Entropy is “time’s arrow”
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Entropy Generation Rate
- Silva (2008)
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Entropy (S) and “Heat-Death”
Universe
∆Suniverse > 0
dS/dt > 0
Energy
Life
∆Slife = 0
• Life is
maintained by
energy input
from the
universe &
entropy export
to the universe
• Does time stop
when dS/dt=0?
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How Did Early Life Get Energy?
• Heterotroph – the ‘premordial soup’ provided
high energy complex molecules that had been
abiotically synthesized (Oparin & Haldane).
– Modern heterotrophs eat other organisms.
• Autotroph – energy derived from oxidation of
ammonia to nitrous & nitric acid, sulfur to
sulfurate, iron to iron oxide, and methane to
carbon dioxide & hydrogen.
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Reverse TCA Cycle
2 CO2 + 4 H2
no catalyst:
very slow
2 H2O + C2O2 (acetate)
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Iron-Sulfur World
- Günter Wächtershäuser
• Life originated on mineral surfaces
near deep hydrothermal vents
(“primordial sandwich”)
• 1st cells were lipid bubbles on
mineral surfaces
• Metabolism predated genetics
with iron sulfides as energy source
(chemoautotrophs)
• Photoautotrophs evolved as
chemical energy was deleted
• Autocatalytic & self-replicating
metabolism
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Thioester World
- de Duve
• Thioester bonds are high energy & played the
role of ATP in early life
• Thioesters are intermediates in the ancient
processes leading to ATP
• Thioesters evolved into ATP
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Driving Force: Entropy & Probability
• Heat is molecular motion
• Most probable configuration has greatest entropy
Less probable (S1)
More probable (S2)
S1 < S 2
• Attractive & repulsive intermolecular forces
determine the most probable configuration
More probable (S4)
Less probable (S3)
S3 < S4
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Simulation of Self-Assembly
http://complex.upf.es/~harold/lipid_world/index.html
Before self-assembly (low S)
After self-assembly (high S)
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Self-Assembly of Liposomes
- Bangham (1961); Deamer (1997, 2002)
Murchinson
Meteorite
extract
Murchinson
Liposomes
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Biological Self-Assembly
• Lipid bi-layer membranes
• Structure guided by attractive & repulsive
forces (“lock-and-key”)
Antibody & antigen
Substrate & enzyme
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Lipid World
- Serge, Ben-Eli, Deamer, Lancet (2000)
• Coacervates. 1-100 μ “proto-cells”
(Oparin 1932)
• Microspheres formed by heatpolymerized amino acids (Fox
1957)
• Murchison carbonaceous
meteorite (Deamer 1997).
Catalytic activity, replication, etc.
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also proposed.
Tobacco Mosaic Virus (TMV)
• TMV self-assembly from separated protein & RNA
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Darwinian Evolution
- Darwin (1959)
• Modified progeny of ‘A’
are better adapted to
the environment &
survive
• Subsequent generations
of ‘B’ – ‘F’ are
unmodified & become
extinct
• Track ‘A’s genealogy into
deep time to find LUCA
• Fossil record too limited
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Systematics or Phylogenetics
- Haeckel (1866)
• Commonality of traits
– Animals – consumers
– Plants – producers
– Protists – reducers
Evolutionary
time
• Eucaryote* – nucleus, etc.
• Prokaryote* – no nucleus
* Stanier (1961)
[common
biochemistry]
• LUCA
• Fossils–no! Genetic code?
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DNA Code
Cytosine
Guanine
Adenine
Thymine
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RNA World
• RNA-based life predated DNA life
• RNA can act as its own catalyst (‘ribozyme’) so
proteins were unnecessary
• RNA evolved into DNA which is more stable
• Ribosomal RNA (rRNA) is a remnant of the
RNA World
• Problems: RNA chemically fragile, difficult to
synthesize abiotically, limited catalysis
42
Pre-RNA Worlds
• Alternative nucleic acids
– RNA precursors: threose nucleic acid (TNA), PNA
(peptose), GNA (glycol)
• PAH (Polycyclic Aromatic
Hydrocarbon) World
– PAHs are amphiphilic and might
self-organize in stacks as a
nucleic acid backbone
43
Clay World
- Cairns-Smith (1985)
• Proto-life was inorganic and existed on solid
surfaces such as clays
• Clays catalyzed formation of complex organic
molecules
• Clays acted as template for RNA self-assembly
and evolved into RNA
• Natural selection enhanced their replication
potential
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Ribosome
- Woese (1981)
• Site of protein synthesis in all cells
– Functionally constant over time
• Ribosomal RNA 16S
– RNA “dictionaries” → phylogenetic trees
– Genotype → phenotype (cell membranes)
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Phylogenetic Tree of Life (16S rRNA)
- Woese (1990)
‘progenotes’
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Horizontal Gene Transfer (HGT)
• ‘Infective heredity’
• Endosymbiosis
– Mitochondria (1.7-2 bya)
– Plastids (1.5 bya)
• Antibiotic resistance
– Plasmids
• Viruses
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Artificial HGT (Social Evolution)
- Craig Venter
• Sequence yeast cell genome (Myoplasma
mycoides)
• Synthesize M. mycoides genome from lab
chemicals
• Transplant synthetic genome into recipient cell
(M. capricolum)
• Test viability of synthetic cell
• Next find minimal viable synthetic genome
• Applications – bio-fuels, vaccines, drugs, etc.
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• What are the limitations of the field?
• What came first: metabolism or replication?
• What would be the result if you could re-run
evolution again beginning from the Big Bang?
• What would be the result if you re-ran
evolution from the Big Bang 1,000 times?
• Is laboratory investigation of the creation of
some form of life valuable?
• If you were in charge of an origin of life lab,
where might you focus your efforts?
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