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Origin & Early Development of LifeRichard Vann

CBI 206/ANESTH 445Physiology and Medicine of Extreme Environments

Spring 2015

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4.6-4.0 bya Hadean

542-488 mya Cambrian

4.0-2.5 bya Achaean 2.5-0.5 byaProterozoic

The Present

488 my

Early ‘Scientific’ Ideas of How Life Began

• Panspermia: life exists throughout the universe• Spontaneous generation: life forms by the action

of the sun on the primordial terrestrial slime

Aristotle384-322 BC

Anaximander611-547 BC

Anaxagoras500?-428 BC

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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

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The Life Force & Urea

• In 1828, Friedrich Wöhler made urea by heating ammonium cyanate & pioneered organic chemistry

• "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."

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• By the 19th Century, organic & non-living compounds were believed to differ because of a Life Force (“élan vital, will-to-live”)

Death of Spontaneous Generation:Louis Pasteur (1859)

• Living systems arise biotically from other living systems• Others postulated there was a single initial abiotic

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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

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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Aleksandr Oparin (1924)

• Unique, abiogenic, spontaneous event that generated life• No difference between lifeless

matter & a living organism• Early Earth atmosphere was

strongly reducing like Jupiter• CH4, NH3, H2O , H2, but no O2

• Sunlight reacted with non-living chemicals in “primeval soup”

• Found evidence for “proto-cells” 9

Harold Urey1893-1981

Stanley Miller1930-2007

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Miller-Urey Ocean-Atmosphere

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Miller (1953). Production of amino acids under possible primitive Earth conditions. Science 117: 528.

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Hydrothermal Volcanic VentsHydrothermal ventsDSV Alvin (1977)

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Tube WormsMollusca

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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Extremophiles

• Acidophile, alkaliphile, anaerobe, cryptoendolith, halophile, hypothermophile (80-122oC), hypolith, metallotolerant, oligotroph, osmophile, piezophile (bathophile), polyextremophile, psychrophile, radioresistant, thermophile (45-122oC), thermoacidophile, xerophile

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YellowstoneRock-Eating Bacteria

• Laboratory Simulations of dry terrestrial environments• Reactants: N2, CO2, S, Fe• Minerals: Fe-S, Ni-S• Products: NH3, amino acids, peptide bonds, C-fixation Fe-

complexes

• Radioastronomy• Organic molecule spectra

• Laboratory simulation• H2O, CO, CH4, NH3 at -100oC with UV

• Murchison meteorite (1969)• 100 amino acids

• NASA satellite samples (cosmic dust)

Organic Molecules from Space

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Origin of Primordial Molecules- Deamer (2002)

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So Where Did Life Originate?• Panspermia (exogenesis)

– Physics & chemistry the same, environments differ– Microbes survive 3-yrs on Moon; impact simulation– Mars in habitable zone 1 bya; meteors, methane

• Astrobiology: origin, evolution, distribution & future of life in the universe

• Rare Earth Hypothesis (Ward & Brownlee 2000)– Simple life is common, complex life is rare requiring

improbable astrophysical & geological events• Consider transition from anaerobic to aerobic respiration

Anaerobic to Aerobic Transition

LHB

OXYGENPHOTOSYNTHESIS

CH4 LIFESURVIVED IN

VOLCANICVENTS

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BIF

O2 CONVERTS CH4 TO CO2 &GREENHOUSE‘SNOWBALL

EARTH.’RELEASE BY

VOLCANIC CO2

GREENHOUSE

O2 RESP

HADEAN ARCHEANPROTEROZOIC

EARLY

H2 & HeATMOSPHEREDISPERSED BY SOLAR WIND

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Cambrian Body Plans

Transition Lessons• Life-environment interactions

– Radioactivity, tectonic plates, volcanoes, oceans, atmosphere, O2 photosynthesis, Fe-cycling, metabolic & Greenhouse gases (CH4, CO2), Snowball Earth

– Higher metabolism promotes more complex life• Aerobes with modern biochem replace anaerobes

– ‘Original’ life & biochemistry lost • Metabolism (ATP, glycolysis, citric acid cycle)• Replication (DNA)

• Last Universal Common Ancestor (LUCA)• Darwin (1859): study fossil record 21

‘Tree of Life’

• Basis for classification – Historical: morphology– Recent: genetic

• ribosomal RNA (rRNA): site of protein synthesis in all cells, functionally constant over time

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Carl Woese1928-2012

• Phylogenetic classification by similar properties– Horizontal dimension: species– Vertical dimension: time LUCA

LUCA 23

Phylogenetic Tree of Life (Woese 1990)

Horizontal Gene Transfer (HGT)

- Woese & Fox (1977)

• Endosymbiosis (2-1.7 bya)– Mitochondria, chloroplasts,

plastids• ‘Infective heredity’ (antibiotic resistance)

– Plasmids

24LUCA?

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Primordial Metabolism• A closed chemical cycle with an energy source &

feedstock molecules (e.g., CO2, H2O, organics)– Sequence of progressively larger molecules – Largest splits into parts identical to earlier molecules &

restarts the cycle– ‘Autocatalytic’ reaction where a product is a reactant

• Objectives– Energy production: capture energy from exothermic

reactions in high-energy bonds (catabolism)– Biosynthesis: use high-energy bonds to promote

energetically unfavorable reactions (anabolism)

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Energy Production: Glycolysis• Ancient pathway used by anaerobes & aerobes• Net ATP production: anaerobes 4, aerobes 30

(pyruvate enters the citric acid cycle)

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Biosynthesis: Reverse Citric Acid Cycle• Forward Citric Acid Cycle used

by all aerobic organisms • Some primitive microbes use

reverse cycle to make carbon compounds from CO2 & H2O– Final step splits to acetate &

oxaloacetate to restart the cycle, doubling in each turn

• Was CO2 used this way before photosynthesis?• Did ancient minerals act as enzymes?• Did the Reverse Cycle originate abiotically?

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Thioester World (de Duve 1995)

• Intermediate in ATP reactions• May have played the role of ATP in

primordial metabolism?• Consistent with hydrothermal vent

extremophile & origin of life hypothesis • Provide chemical coupling to transfer

energy for RNA synthesis?

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Iron-Sulfur World- Günter Wächtershäuser (1992)

• Life originated in volcanic vents on iron sulfide minerals that acted as catalysts – “primordial sandwich”

• Carbon fixation was autocatalytic in a sulfur-dependent citric acid cycle

• Last step was lipid membrane synthesis and led to the LUCA

Primordial Replication: RNA World… (Woese 1967)

• RNA-based life predated DNA life• RNA can act as a catalyst (‘ribozyme’)

so protein enzymes were not needed

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• 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

Pre-RNA Worlds• Alternatives to nucleic acids in DNA

– RNA precursors: threose nucleic acid (TNA), PNA (peptose), GNA (glycol)

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• PAH (Polycyclic Aromatic Hydrocarbon) World– Found in space– Amphiphilic & might self-

organize in stacks as a nucleic acid backbone

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 replication potential

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Self-Assembly

• Liposome self-assembly & ‘Lipid World’• Carbon residues on Murchison

meteorite (Deamer 1997) 33

• Coacervates: 1-100 μ ‘proto-cells’ selectively absorb solutes (Oparin 1932)

• Heat-polymerized amino acids form double-wall 2 μ ‘microspheres’ (Fox 1957)

• Isolate high-energy molecules & other cellular components from the environment

Self-Assembly of Liposomes- Bangham (1961); Deamer (1997, 2002)

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MurchinsonMeteoriteextract

MurchinsonLiposomes

Biological Self-Assembly• Lipid bi-layer membranes

35Antibody & antigen Substrate & enzyme

• Attractive & repulsive (‘lock-and-key’) forces guided by tertiary protein structure

Tobacco Mosaic Virus (TMV)• TMV self-assembly from separated protein & RNA

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Thermodynamic Basis of Self-Assembly

• 1st Law: energy is conserved, not created or destroyed & all forms are inter-convertible

• 2nd Law: energy conversions are never perfect– Some energy is always rejected to the environment

as wasted heat (q) – Entropy (S) = wasted heat divided by the

environmental temperature (S = q/T)– Entropy is generated with each energy conversion

Entropy is “time’s arrow”

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Entropy & Random Thermal Motion

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• More order• Lower entropy

• Less order• Higher entropy

• Random thermal motion increases disorder• A disordered system has higher entropy

Gas molecules

• Hydrogen bonding attracts H2O & polar heads• Molecules move by random thermal motion to reduce attraction

Aqueous Solution- Polar H2O

- Polar head- Lipid tail

• Exogenesis– Can’t rule out for simple life

• Transition from primordial anaerobic life to modern life– Environmental interactions were prerequisite– Common ancestral community of primitive cells

• Primordial metabolism & replication– O2 photosynthesis & respiration

• Self-assembly & forward direction of time – Thermodynamics & random thermal motion

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Summary

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