Early Earth

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					Hypotheses of Early Life: Cenancestor
             formation
         (4 main phases)
      1. Abiotic synthesis (inorganic > organic)
          Oparin & Haldane hypothesis
          (1920s)
          Urey & Miller (1953)

      • Joining of monomers > polymers
           Fox (1950s-60s)

      • Packaging of protobionts
          Oparin hypothesis (1920s)
          Fox (1950s-60s)

      • Self-replicating molecules
          Cech (1980s)
          Altman (1980s)
Hypotheses of Early Life: Cenancestor
             formation
         (4 main phases)
      1. Abiotic synthesis (inorganic > organic)
          Oparin & Haldane hypothesis
          (1920s)
          Urey & Miller (1953)

      • Joining of monomers > polymers
           Fox (1950s-60s)

      • Packaging of protobionts
          Oparin hypothesis (1920s)
          Fox (1950s-60s)

      • Self-replicating molecules
          Cech (1980s)
          Altman (1980s)
   Abiotic synthesis: Early Earth
            environment

• Oparin & Haldane Hypothesis (1920s)
• No O   2

• Reducing environment favors synthesis
• CO NH H H O CH H S
     2       3   2   2   4   2

• Lightning, UV irradiation, etc.
• “Primordial Soup” hypothesis
     Miller and Urey,
• Bottom flask 1953 vaporization
               heated >
• Electric sparks applied to top flask
• Ran for 1 week
• Results:
     • Water became pink, then red,
       and turbid
     • Analysis of contents reveals
       organic compounds
        • amino acids (alanine and
          glycine)
        • sugars
        • lipids
        • building blocks of nucleic acids




   Stanley Miller, Age 23
Hypotheses of Early Life: Cenancestor
             formation
         (4 main phases)
      1. Abiotic synthesis (inorganic > organic)
          Oparin & Haldane hypothesis
          (1920s)
          Urey & Miller (1953)

      • Joining of monomers > polymers
           Fox (1950s-60s)

      • Packaging of protobionts
          Oparin hypothesis (1920s)
          Fox (1950s-60s)

      • Self-replicating molecules
          Cech (1980s)
          Altman (1980s)
Sydney Fox: Simple polymers (1950s)
       • amino acids (monomers)
       • Heat
        • Hot sand, clay, rock
       • polypeptides (polymers)
     *dripped amino acids over hot sand, clay, rock
     and found that given the proper conditions,
     monomers would join to form polymers
     *in same manner were able to form proteinoids
     (a type of protobiont) as outlined in next section
Hypotheses of Early Life: Cenancestor
             formation
         (4 main phases)
      1. Abiotic synthesis (inorganic > organic)
          Oparin & Haldane hypothesis
          (1920s)
          Urey & Miller (1953)

      • Joining of monomers > polymers
           Fox (1950s-60s)

      • Packaging of protobionts
          Oparin hypothesis (1920s)
          Fox (1950s-60s)

      • Self-replicating molecules
          Cech (1980s)
           Altman (1980s)
Protobionts: aggregates of abiotically
 produced molecules surrounded by
• Oparin (1920s)membrane
                coined the term
•   “bubble hypothesis”
•   Sydney Fox (1950s-60s) demonstrated with
    proteins as “membrane” (proteinoids)
•   Maintain internal chemical environment
    separate from surroundings
•   Some properties associated with life
    •   reproduction- can “duplicate” & “divide”
    •   “metabolism”- can take up substances;
        can set up simple metabolic reactions
        inside
                     Protobionts
 •synonyms and different names depending on what
 “membrane” is made of:
coacervates, proteinoids, micelles, liposomes, microspheres
          Liposome formation
• Amphiphilic lipids form micelles and
  liposomes
• Hydrophilic (water-loving) heads and
  hydrophobic (water-hating) tails self-
  assemble in agitated H2O
• Can grow and shrink in the presence of
  salts
Protobionts: fossil evidence
   3.5 billion years ago
Hypotheses of Early Life: Cenancestor
             formation
         (4 main phases)
      1. Abiotic synthesis (inorganic > organic)
          Oparin & Haldane hypothesis
          (1920s)
          Urey & Miller (1953)

      • Joining of monomers > polymers
           Fox (1950s-60s)

      • Packaging of protobionts
          Oparin hypothesis (1920s)
          Fox (1950s-60s)

      • Self-replicating molecules
          Cech (1980s)
          Altman (1980s)
   Ribozymes & the “RNA World”

Ribozymes = RNA as an enzyme


  • RNA-directed catalysis discovered in
    nature (1980s)
       • Tom Cech - self splicing introns
       • Syndey Altman - tRNA cleavage
  Self-replicating Ribozyme (2001)
“RNA polymerase ribozyme” made in
                  lab
                   “R
        Ribozymes & the “RNA World”
•   RNA may have been the first genetic material
    •   RNA simpler than DNA
    •   error-prone polymerization produces “mutations”-
        diversity in “offspring”
    •   natural selection of “offspring” with more efficient
        catalysis leads to “evolution”
    •   idea that enzymatic activity appears first and
        specificity evolves later
       Ribozymes & the “RNA World”

Modern precedent for idea of RNA as self-
replicating genetic material
   •   RNA viruses: RNA as sole genetic material
       (no DNA intermediates)
   •   RNA molecules involved in many types of
       polymerization in “modern” cells
       •   Telomere (DNA end structures) replication
       •   Ribosome and tRNA (Translation)
  What is missing from early Earth
atmosphere that we need in order to
   progress to the 3 Domains?
Hypothesis: Going from Cenancestor to 3
                Domains
I. Prokaryotes oxygenate the atmosphere

•cellular metabolism evolved in
prokaryotes
•first organisms are chemoheterotrophs
    •no oxygen in atmosphere (so
    anaerobic)
    •only food is organic matter in
    primordial soup
                Domains
I. Prokaryotes oxygenate the atmosphere


•second to evolve are simple autotrophs
   •give off oxygen as by product
   •this leads to the oxygenation of atmosphere
   •some hypothesize that these were
   photosynthetic Cyanobacteria-like organisms
   •third to evolve are heterotrophs that use
   oxygen (aerobic)
Hypothesis: Going from Cenancestor to 3
                Domains
I. Prokaryotes oxygenate the atmosphere



This is the Heterotroph Hypothesis:

chemoheterotrophs > autotrophs > heterotrophs
  no O2 present     produce O2    use O2
   Hypothesis: Going from Cenancestor to 3
                   Domains
   II. Going from prokaryotes to eukaryotes

•First, membrane in-folding created
endoplasmic reticulum and nucleus
      Hypothesis: Going from Cenancestor to 3
                      Domains
      II. Going from prokaryotes to eukaryotes
  Endosymbiotic Theory
 •second, endosymbiosis
 led to formation of
 mitochondria and
 chloroplasts
                                       chloroplasts
                                           from
mitochondria from                     photosynthetic
  heterotrophic                         prokaryote
    (aerobic)                        (Cyanobacteria
    prokaryote                               ?)
  Modern evidence for Endosymbiotic
               Theory
Mitochondria and chloroplasts are prokaryote-
                    like

				
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posted:4/11/2012
language:English
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