The Prebiotic Chemistry of Pyrite: Molecular Scaffold & Catalyst ABIOL 570 November 21, 2004
Introduction <ul><li>Protocellular Scaffold </li></ul><ul><ul><li>Framboidal Pyrite </li></ul></ul><ul><ul><ul><li>A self-...
Phase Separation <ul><li>Adsorption on a surface </li></ul><ul><ul><li>Mineral-H 2 O  </li></ul></ul><ul><ul><li>Air-H 2 O...
Framboidal Pyrite <ul><li>Self-organization:   “the autonomous passage of a system from an unpatterned to a patterned stat...
Framboidal Pyrite <ul><li>Closely-packed, spheroidal clusters of 100-100,000 pyrite microcrystals </li></ul><ul><li>May be...
Framboidal Pyrite <ul><li>Forms instantaneously in anoxic sediments </li></ul><ul><li>Texture is result of rapid nucleatio...
A porous, catalytic scaffold… <ul><li>Fatty Acid vesicles can be forced to divide by extrusion through porous substances… ...
The First “Membranes” <ul><li>Spontaneously form proteinoid microspheres  (electrostatic interactions) </li></ul><ul><ul><...
Fatty Acid Vesicles <ul><li>Phosphates + Glycerol + Fatty Acids  </li></ul><ul><li>   Phospholipids </li></ul><ul><li>Clu...
Creation of Protocells <ul><li>Microsphere can pick up an ything … even liposomes </li></ul><ul><li>ATP + nucleotides    ...
Primitive Protocell Metabolism <ul><li>Precursors needed to maintain “membranes” </li></ul><ul><ul><li>Proteins, lipids & ...
Origin of Heredity & Metabolism <ul><li>RNA most likely not first genetic system </li></ul><ul><li>TNA suggested but linki...
A  T NA World? <ul><li>(L)- α –threofuranosyl-(3 1  2 1 ) oligonucleotide </li></ul><ul><ul><li>Threose is the sugar </li...
A  T NA World? <ul><li>Easily forms hairpins </li></ul><ul><li>much more stable to hydrolytic cleavage than are RNAs and m...
Mineral Catalysis…  remember the  framboidal pyrite ? <ul><li>A multifunctional surface! </li></ul><ul><ul><li>Implicated ...
Pyrite Catalysis <ul><li>Bases arranged in planar arrangement </li></ul><ul><li>Adsorbed purines (attached by van der Waal...
Pyrite Catalysis <ul><li>FeS+ H 2 S  FeS 2 </li></ul><ul><ul><li>Reducing power that could convert CO 2   C-containing m...
Pyrite Catalysis <ul><li>Fe implicated in e- transfer </li></ul><ul><ul><li>Light-driven generation of H 2  gas </li></ul>...
A tantalizing possibility! <ul><li>The first life form may have been photosynthetic!  You’re kidding, right? </li></ul>htt...
Earliest Photosynthesizers <ul><li>Anaerobic environment </li></ul><ul><li>1 st  photosynthesizers used H 2  or H 2 S as s...
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Prebiotic Pyrite Chemistry Molecular Scaffold & Catalyst 1 21

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Jordan-Ohmoto model of abiogenesis whereby framboidal pyrite serves as a photocatalytic scaffold in crucial prebiotic chemical reactions such as liposome nucleation, NTP hydrolysis, and peptide synthesis.

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Prebiotic Pyrite Chemistry Molecular Scaffold & Catalyst 1 21

  1. 1. The Prebiotic Chemistry of Pyrite: Molecular Scaffold & Catalyst ABIOL 570 November 21, 2004
  2. 2. Introduction <ul><li>Protocellular Scaffold </li></ul><ul><ul><li>Framboidal Pyrite </li></ul></ul><ul><ul><ul><li>A self-organizing system </li></ul></ul></ul><ul><ul><ul><li>Synthesized with or without oxygen </li></ul></ul></ul><ul><ul><ul><li>Physical properties of astrobiological significance </li></ul></ul></ul><ul><li>Catalysis </li></ul><ul><ul><li>Adsorption of 5’-AMP onto FeS 2 </li></ul></ul><ul><ul><ul><li>Modulation by acetate </li></ul></ul></ul><ul><ul><ul><ul><li>Readily synthesized under prebiotic conditions </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Common component of metabolic pathways </li></ul></ul></ul></ul><ul><ul><ul><li>Simulated prebiotic environment </li></ul></ul></ul><ul><ul><ul><ul><li>5’-AMP inihibitor (DMF) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Interactions on mineral surface </li></ul></ul></ul></ul>
  3. 3. Phase Separation <ul><li>Adsorption on a surface </li></ul><ul><ul><li>Mineral-H 2 O </li></ul></ul><ul><ul><li>Air-H 2 O </li></ul></ul><ul><ul><li>FeS 2 -H 2 O </li></ul></ul><ul><li>Trapping in a container </li></ul><ul><ul><li>Oil droplets </li></ul></ul><ul><ul><li>Proteinoids </li></ul></ul><ul><ul><li>Amphiphile vesicles </li></ul></ul>http://tycho.bgsu.edu/~laird/ast305/class/IVC-5.html
  4. 4. Framboidal Pyrite <ul><li>Self-organization: “the autonomous passage of a system from an unpatterned to a patterned state without the intervention of an external template”. </li></ul>
  5. 5. Framboidal Pyrite <ul><li>Closely-packed, spheroidal clusters of 100-100,000 pyrite microcrystals </li></ul><ul><li>May be synthesized in 1 of 2 ways: </li></ul><ul><ul><li>FeS (ppt) + S (aq)  Fe 3 S 4  FeS 2 (Low [O 2 ]) </li></ul></ul><ul><ul><ul><li>Greigite = magnetic thiospinel; formation determines rxn rate in the presence of oxygen </li></ul></ul></ul><ul><ul><li>FeS (mk) + H 2 S (aq)  FeS 2(py) + H 2(aq) (no O 2 ) </li></ul></ul><ul><ul><ul><li>Most rapid rxn </li></ul></ul></ul>
  6. 6. Framboidal Pyrite <ul><li>Forms instantaneously in anoxic sediments </li></ul><ul><li>Texture is result of rapid nucleation where pyrite is supersaturated </li></ul><ul><ul><li>Normal saturation: single crystals form </li></ul></ul>
  7. 7. A porous, catalytic scaffold… <ul><li>Fatty Acid vesicles can be forced to divide by extrusion through porous substances… </li></ul><ul><li>Liposomes range in size from 50-60 nm up to Giant Vesicles of 30-100 um </li></ul><ul><li>Framboidal or weathered FeS 2 fits the bill! </li></ul>
  8. 8. The First “Membranes” <ul><li>Spontaneously form proteinoid microspheres (electrostatic interactions) </li></ul><ul><ul><li>Able to take up molecules & have electrical potentials across “membranes” </li></ul></ul><ul><ul><li>Respond to changes in osmotic pressure </li></ul></ul>http://www.biologie.uni-hamburg.de/b-online/e41/3.htm
  9. 9. Fatty Acid Vesicles <ul><li>Phosphates + Glycerol + Fatty Acids </li></ul><ul><li> Phospholipids </li></ul><ul><li>Clumped together </li></ul><ul><ul><li>Phospholipid Bilayers </li></ul></ul><ul><ul><li> Liposomes </li></ul></ul><ul><ul><ul><li>Acquire many different solutes while drying </li></ul></ul></ul><ul><ul><ul><li>Preferred size in range of living cells! </li></ul></ul></ul>www.bio.davidson.edu/Courses/Molbio/MolStudents/.../Favorite_Molecular_Tool.html
  10. 10. Creation of Protocells <ul><li>Microsphere can pick up an ything … even liposomes </li></ul><ul><li>ATP + nucleotides  oligonucleotides (inside ingested liposome) </li></ul><ul><ul><li>Began to base pair with itself? </li></ul></ul><ul><li>Liposomes + hollow proteins  “membrane” pores </li></ul>http://www.stc.uniroma2.it/cfmacro/cfmacroindex.htm
  11. 11. Primitive Protocell Metabolism <ul><li>Precursors needed to maintain “membranes” </li></ul><ul><ul><li>Proteins, lipids & carbohydrates </li></ul></ul><ul><ul><li>First chemoorganotroph (popular; simple metabolism) </li></ul></ul><ul><ul><li>Protocells died when starved, became toxic, got too big or in wrong environment </li></ul></ul><ul><ul><li>Some grew faster than others, made products that facilitated growth, etc. </li></ul></ul>http://www.funhousefilms.com/sciencpg.htm
  12. 12. Origin of Heredity & Metabolism <ul><li>RNA most likely not first genetic system </li></ul><ul><li>TNA suggested but linking bases, sugars & PO 4 ’s has not been demonstrated </li></ul><ul><li>Mineral catalysis? </li></ul>http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=189
  13. 13. A T NA World? <ul><li>(L)- α –threofuranosyl-(3 1  2 1 ) oligonucleotide </li></ul><ul><ul><li>Threose is the sugar </li></ul></ul><ul><li>Simplest nucleic acid alternative </li></ul><ul><ul><li>Possible ancestor of RNA </li></ul></ul><ul><ul><li>Possible protector/regulator of RNA (binds to it) </li></ul></ul><ul><li>Forms base pairs </li></ul><ul><ul><li>G = C & T/U=A </li></ul></ul><ul><ul><li>Informational in anti-parallel </li></ul></ul><ul><ul><li>Cross-pairs with RNA & DNA </li></ul></ul><ul><li>A & T nucleobase analogs: </li></ul><ul><ul><li>2’-amino-(2’-NH2 TNA) </li></ul></ul><ul><ul><li>3’-amino-(3’-NH2 TNA) </li></ul></ul><ul><li>Bst PolI, bacteriophage T7 DNA Pol (exo-) & MMLV-RT </li></ul>Chaput, J.C., Ichida, J.K & Szostak, J.W. (2002) DNA Polymerase-Mediated DNA Synthesis on a TNA Template . J. AM. CHEM. SOC. 125, 856-857.
  14. 14. A T NA World? <ul><li>Easily forms hairpins </li></ul><ul><li>much more stable to hydrolytic cleavage than are RNAs and may be as stable as DNAs </li></ul><ul><li>TNA strands can be synthesized by template-controlled ligation with either complementary TNA or RNA strands as templates </li></ul><ul><li>corresponding formation of RNA sequences by ligation on a TNA template does also occur, although with less efficiency </li></ul>http://www.scripps.edu/research/sr2001/chm03.html
  15. 15. Mineral Catalysis… remember the framboidal pyrite ? <ul><li>A multifunctional surface! </li></ul><ul><ul><li>Implicated in: </li></ul></ul><ul><ul><ul><li>Reverse Citric Acid Cycle </li></ul></ul></ul><ul><ul><ul><li>LPS of bacteria in bioleaching </li></ul></ul></ul><ul><ul><ul><li>CO 2 fixation (+ H 2 S) </li></ul></ul></ul><ul><ul><li>Purine can adsorb to uncharged sites on FeS 2 surface! </li></ul></ul>
  16. 16. Pyrite Catalysis <ul><li>Bases arranged in planar arrangement </li></ul><ul><li>Adsorbed purines (attached by van der Waals interactions) may have paired with pyrimidines (H-bonding) </li></ul><ul><li>Enclosure by vesicles act as reaction vessels </li></ul><ul><li>Wachtershauser: 2-D surface ↑ organization </li></ul>
  17. 17. Pyrite Catalysis <ul><li>FeS+ H 2 S  FeS 2 </li></ul><ul><ul><li>Reducing power that could convert CO 2  C-containing metabolites </li></ul></ul><ul><ul><li>Directly to CO 2 failed but successful from CO (Stetter et al.) </li></ul></ul><ul><ul><li>CO 2 + FeS + 2 H 2 S  FeS 2 + 2 H 2 O + C </li></ul></ul><ul><ul><ul><li>FeS needs higher reductive power to fix CO 2 </li></ul></ul></ul><ul><ul><ul><li>Possible with additional energy input </li></ul></ul></ul>
  18. 18. Pyrite Catalysis <ul><li>Fe implicated in e- transfer </li></ul><ul><ul><li>Light-driven generation of H 2 gas </li></ul></ul><ul><ul><li>Oxidative/Reductive rxns catalyzed by Fe-S minerals (FeS 2 ) </li></ul></ul><ul><ul><ul><li>Adoption of Fe-S clusters in: </li></ul></ul></ul><ul><ul><ul><ul><li>Ferredoxines </li></ul></ul></ul></ul><ul><ul><ul><ul><li>N-fixing enzymes </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Many other cofactors </li></ul></ul></ul></ul><ul><ul><li>Solubilization of FeS 2 by Cys  dissolved chemical energy </li></ul></ul><ul><ul><li>Semiconducting Properties </li></ul></ul><ul><ul><ul><li>Adsorption Constant of α = 6E5 cm -1 for h v >1.8 eV) </li></ul></ul></ul><ul><ul><ul><li>High quantum efficiencies (up to 90% of adsorpbed photons generate e- hole pairs in the sulfide) </li></ul></ul></ul>
  19. 19. A tantalizing possibility! <ul><li>The first life form may have been photosynthetic! You’re kidding, right? </li></ul>http://www.bact.wisc.edu/bact330/lecturestaph
  20. 20. Earliest Photosynthesizers <ul><li>Anaerobic environment </li></ul><ul><li>1 st photosynthesizers used H 2 or H 2 S as substrates </li></ul><ul><li>Microbes still do this (H 2 S  H 2 + S) </li></ul><ul><ul><li>Purple & green sulfur bacteria </li></ul></ul>http://bio.winona.msus.edu/bates/Bio241/images/figure-08-12-2.jpg
  21. 21. Questions?

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