Primordial%20Soup%20in%20the%20Kitchen%20of%20Life:

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Primordial Soup in the Kitchen of Life The
Origin of Life
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How Do We Classify Life ?
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Three Domains
Archaea
Eukarya
Bacteria
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Revised to
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And Viruses ?
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And nanobacteria ?
Nanobes growing on clay ?
Note Nanobacteria about 1,000 x smaller than
regular bacteria disagreement lies in whether
or not nanobes are Too small to contain genetic
material
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Recall Evolution of Earths Atmosphere

• Initial atmosphere much like Jupiter
• (rich in Hydrogen and Helium derived from solar
  nebula)
• - burned off by Solar Wind / escaped weak
  gravitational field
• 2. Second atmosphere much like Venus
• (dominated by carbon dioxide from Earths
  interior)
• - The Big Burp
• 3. Third and present atmosphere
• (rich in oxygen)
• - modified from second atmosphere due to rise of
  anaerobic,
• photosynthesizing organisms

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Some Basic Characteristics of Living Things

• Metabolism Living things harvest energy from
  environment, use energy to build, maintain their
  bodies.
• Regulation Living things have a complex,
  integrated system that controls conditions within
  their bodies.
• Replication Living things can produce offspring.
• Response to external stimuli Living things
  respond to conditions of their external
  environment as individuals and larger populations.

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Basic Stages Envisaged In The Development of Life
Raw Ingredients Monomers Polymers Cell
Membrane Reproduction Living Cell
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Raw Ingredients Monomers Polymers Cell
Membrane Reproduction Living Cell
Raw ingredients assumed to have been present in
atmosphere and hydrosphere of Early
Earth water carbon dioxide carbon
monoxide N-gases S-gases methane ?
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Raw Ingredients Monomers Polymers Cell
Membrane Reproduction Living Cell
Monomers demonstrated to be capable of forming
abiotically in Miller experiment (and
variants) gas mixture including water, methane,
ammonia, hydrogen energy yields amino acids,
sugars, nucleic acid bases, lipids
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Miller-Urey Experiment (Spontaneous Generation)
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Products of Miller-Urey Experiments (1953-59)
Most important Amino acids (building blocks of
proteins) (alanine, glycine)
Ponnamperuma et al (1963) - used high energy
electrons on a mixture of methane, water and
ammonia - adenine, ribose and deoxyribose
synthesised abiotically.
Problem Ingredients used not concentrated in
volcanic emissions (therefore probably not in
early atmosphere either)
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Raw Ingredients Monomers Polymers Cell
Membrane Reproduction Living Cell

• Polymers assumed to form through
• concentration, dehydration of monomers
• through
• Evaporation of solution near hot springs
• Freezing and concentration of solution in cold
  environments
• Adsorption onto charged mineral surfaces

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Areas where monomers could be concentrated
Deep sea vents ?
Hot springs ?
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Ponds in Cold areas ?
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Polymerization of Simple Organic Molecules By
Mineral Templates ?
Clay minerals
Feldspar
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Big Problem Polymerization to Form Genetic
Material
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Raw Ingredients Monomers Polymers Cell
Membrane Reproduction Living Cell
Cell membrane was required to form the first
isolated cell (to contain the necessary complex
molecules). Lipids can spontaneously form
liposomes (hollow spheres of lipids) . Also,
proteins will form microspheres when dehydrated
and agitated. Important Properties of these
tiny spheres 1. Maintain separate stable phases
in water 2. Membrane maintains electric, pH and
redox gradients.
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Coacervates Cell Wall ?
Can be produced from amino acids (like oil in
salad dressing)
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Raw Ingredients Monomers Polymers Proto-Cell
Reproduction Living Cell
Advent of Reproduction very problematic in
abiogenic models. Main Problem Chicken and
Egg
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CHICKEN-EGG PROBLEM
Synthesis and replication of RNA today happens
with help of enzymes (proteins). Proteins are
synthesized using coded information in RNA or DNA
RNA
proteins
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RNA World (The Naked Gene)

• RNA can function as both
• information molecules
• that can be replicated
• and
• 2. catalysts (like protein enzymes)
• as ribozymes

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Rationale of Naked Gene Hypothesis 1. Earliest
life form was an energy-harvesting RNA molecule
that could catalyze its own replication. 2. The
RNA molecules most efficient at energy
harvesting and protecting themselves from
environmental changes would win over less
effective individuals. 3. Natural selection
would build complex metabolic and regulation
systems incorporating protein enzymes. 4. RNA
that could replicate in double-stranded form
would proliferate since these forms would have
two copies of each code, allowing better
detection of errors in code
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Making genetic material abiotically isnt
impossible, but it aint walk in the park
either Problems 1. RNA, DNA very complex
molecules 2. Need high concentrations of
building blocks to concentrate and
polymerize. 3. Replication of RNA a TWO STEP
process Single strand of RNA present, each of
its links attract complimentary link (mirror
image) out of prebiotic soup like making a
zipper from one side as template for the
other Process would have to be repeated using
new mirror image to duplicate original side
(requires enzymes).
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Did replication start from proteins ? (Scenario
by Sydney Fox)

• Imagine
• Sheltered lagoons filled with tiny proteinoid
  microspheres.
• 2. Protenoids catalyze chemical reactions and
  form outer surfaces acting like cell membranes.
• Nucleic acids (DNA, RNA) formed on proteinoid
  enzyme templates.
• 4. DNA (or RNA) evolve to function as
  replicator molecules.
• Splitting and fusion of microspheres with
  exchange of material

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Another Approach The Clay Critter Revisited

• Properties of mineral crystals
• The result of atoms naturally organizing
  themselves
• Organization at micro- and macro- scale
• Clay minerals electrostatically charged, grow by
  adding
• layers to themselves (like pages in a book).
• 4. When broken, the fragments can continue to
  grow
• on their own (abiotic reproduction).

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Clay Critter Scenario

• Growing clay crystals compete with each other for
  resources as they grow.
• 2. Crystals break apart, be transported in new
  area where they continue to grow and fragment
  again in effect, the world is populated with
  competing clay beings.
• 3. Genetic code in effect, charged mineral
  surfaces.
• 3. Eventually, clay critters begin to adsorb and
  incorporate carbon based molecules to apparatus
  (e.g. proteins).
• 4. Synthesis of DNA or RNA to augment and
  ultimately replace clay-based genes.

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Panspermia Hypothesis (Earths Life Originated
Elsewhere)
Fossils from ALH84001
KINDA COOL, BUT DODGES THE FUNDAMENTAL QUESTIONS
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END OF LECTURE