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Chapter 26 powerpoint-early earth and origin of life

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					Early Earth and Origin of Life

          Chapter 26
• Earth’s original organisms are microscopic and
  unicellular.
• Life on Earth originated b/w 3.5- 4 billion years ago.
• Earth formed 4.5 billion years ago.

• Evidence of ancient prokaryotes found in rocks called
  stromatolites- banded domes of sedimentary rock
  similar to layered mats formed today in salt marshes
  and some warn ocean lagoons by colonies of bacteria
  and cyanobacteria. The layers are sediments that
  stick to jelly-like coats of motile microbes, which
  continually migrate out of one layer of sediment and
  form a new one above, producing the banded pattern
          Major episodes in the history of life
•   1. Origin of Earth
•   2. Earth cool enough for crust to solidify
•   3. Origin of life (prokaryotes)
•   4. RNA sequence data shows prokaryotes split into 2 groups: bacteria and
    archae
•   5. Production of oxygen by early photosynthetic prokaryotes create
    aerobic atmosphere, and organisms must adapt to being aerobic, and
    species set to evolve
•   6. Origin of eukaryotes: protists- large, disparate group of unicellular
    eukaryotes and some closely related multicellular organisms
•   7. Origin of multicellular organisms: Plant, fungi, and animals. (fungi more
    related to animals than plants) in PreCambrian
•   8. Late PreCambrian: oldest animal fossils
•   9. Plants and symbiotic fungi colonize land: Paleozoic
•   10. Extinction of Dinosaurd at end of Mesozoic
•   11. First humans at end of Cenozoic
First organisms were products of chemical evolution in
                       4 stages:

• 1. The abiotic (nonliving) synthesis and accumulation of small
  organic molecules (monomers) such as amino acids and
  nucleotides

• 2. Joining of these monomers into polymers (proteins and
  nucleic acids)

• 3. Aggregation of abiotically produced molecules into droplets
  (protobionts) that had chemical characteristics different from
  surroundings.

• 4. Origin of heredity (before droplet stage)
              Oparin-Haldane Hypothesis

• In the present atmosphere, oxygen is rich and attach
  chemical bonds, extracting electrons. Before oxygen
  producing photosynthesis, Earth had a much less
  oxidizing atmosphere. Such a reducing (electron
  adding) atmosphere would have joined simple
  molecules to form complex ones. This requires a lot of
  energy, possible provided from lightning, intense UV
  radiation, and volcanic vapors from the atmosphere
  back then. Today, the oxygen has produced an ozone
  layer that prevents UV radiation.
              Stanley Miller and Harold Urey

• They tested Oparin-Haldane hypothesis by creating
  experiment similar to Earth’s early atmosphere: used an
  apparatus where a warm flask of water represented the sea.
  The atmosphere had (H20-water, H2-hydrogen, CH4-methane,
  and NH3-ammonia). Sparks were discharged in the fake
  atmosphere to mimic lightning. A condenser cooled the
  atmosphere, raining water and other dissolved compunds
  back to the sea. As material circulated through the apparatus,
  the solution in flask turns clear murky brown. After one
  week, variety of organic compounds including amino acids
  that make up proteins of organisms, were found.
                          Protobionts

• Living cells may have been preceded by protobionts
  (abiotically produced molecules)- cannot reproduce, but
  maintain internal environment diff. from surroundings and
  exhibit some properties similar to life such as metabolism and
  excitability.

• Coacervate (a protobiont) is a stable droplet that tends to self-
  assemble when a suspension of macromolecules is shaken.
  Hydrophobic macromolecules surround coacervate, which
  absorb substrates from enzymes and release products of
  reactions catalyzed by the enzymes.
• Protobionts could have formed spontaneously from abiotically produced
  organic compounds:

• Microspheres made by cooling solutions of proteinoids (polypeptides
  created abiotically from amino acids polymerized on hot surfaces).
  Microspheres grow by absorbing free proteinoids until they reach unstable
  size, and split to form daughter microspheres.

• In aqueous environ., certain lipids self-assemble to form liposomes, which
  some grow by engulfing smaller liposomes and then splitting, other times
  giving birth” to smaller liposomes.
            RNA is first genetic material


• RNA is autocatalytic, and in prebiotic world,
  RNA molecules capable of self-replication:
• RNA acts as template for making
  polypeptides; and in turn the polypeptides act
  as enzymes that aid in the replication of RNA
  molecules.
• Within a membrane, polypeptides aid the
  replication of only the template RNA genes.
    Were RNA or DNA genes preceded by simpler
               hereditary systems?


• Amino-adenosine triacid ester (AATE) ,
  consists of amino adenosine and an ester.
• AATE can catalyze synthesis of another AATE
  by acting as a template.
             THE END



• This has been a slideshow by SUPER-
  LAUREN! She rox sox!

				
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posted:12/18/2011
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