Endosymbiotic Theory Short Lecture

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endosymbiotic theory for introductory college biology class

endosymbiotic theory for introductory college biology class

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  • 1. The Endosymbiotic Theory and the Origin of Eukaryotic Cells BIO 101: General Biology I
  • 2. Earth’s Earliest Inhabitants
    • Earliest direct evidence of life dates from 3.5 billion years ago (BYA)
    • Prokaryotic organisms were the sole inhabitants of Earth until around 2.1 BYA
    • These anaerobic prokaryotic organisms transformed life on Earth
      • Helped create hospitable environment for other types of organisms
  • 3. Oxygen Revolution
    • Most atmospheric oxygen (O 2 ) comes from a biological source
    • Levels of atmospheric O 2 increased slowly from 2.7 to 2.3 BYA, then shot up quickly
      • Ancestors of modern cyanobacteria (O 2 -releasing, photosynthetic bacteria) contributed to this O 2 increase
  • 4. The Changing Atmosphere and the Endosymbiotic Theory
    • Some anaerobic prokaryotes adapted to the new environment
      • Cellular respiration is a process in which oxygen is used to harvest energy from organic molecules
    • How did aerobic prokaryotic cells living in this changed environment lead to eukaryotic cells?
    • The Endosymbiotic Theory
      • Endosymbiont is a cell that lives within another cell, referred to as a host cell
  • 5. Development of Endosymbiosis
    • Aerobic heterotrophic prokaryotes were engulfed by other cells
    • Provide oxygen utilization to an anaerobic host cell enabling it to survive in the more oxygen rich environment
    • Mitochondria - the site of cellular respiration
  • 6. Development of Endosymbiosis
    • Evidence supporting the Endosymbiotic Theory:
    • Enzymes and transport systems are homologous to those in living prokaryotes
    • Replicate by binary fission
    • Contain own DNA and ribosomes
  • 7. Modern Model of Endosymbiosis & Eukaryotic Cell Origin
    • Crithidia deanei – protozoan parasite of insects
      • Harbors obligate intracellular bacterium, an endosymbiont
    • Endosymbiont contains it own DNA but cannot survive and replicate outside of host protozoa
    • Endosymbiont is replicated and passed to daughter cells
  • 8. Endosymbiont Passed to Daughter Cells
    • Image legend: N=nucleus; S=symbiont
    • Model for studying eukaryotic cell evolution
    • Understanding could tell us something about how mitochondria and chloroplasts came to be eukaryotic organelles.
    • Motta, et al . PLoS ONE. 2010; 5(8)
  • 9. References
    • Reece, J., et al. Campbell’s Biology, 9 th ed. San Francisco: Pearson Benjamin Cummings; 2011.
      • Source of all figures unless otherwise cited
    • Motta MCM, Catta-Preta CMC, Schenkman S, Martins ACdA, Miranda K, et al . The bacterium endosymbiont of Crithidia deanei undergoes coordinated division with the host cell nucleus. PLoS ONE. 2010; 5(8):e12415. doi:10.1371/journal.pone.0012415. Accessed March 26, 2011.