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The Origin of Eukaryotic Cells
Serial Endosymbiotic Theory (SET): Chloroplasts and Mitochondria evolved from symbiotic bacteria that lived inside of a larger prokaryote
Clay-mation• https://www.youtube.com/watch?v=EgaGh9-mFnQ
Outline•What is the evidence for endosymbiosis?•What role did endosymbiosis play in the origin of life?•How does endosymbiosis change our view of the branching pattern on the tree of life?
Discuss•“Nothing in molecular biology makes sense expect in light of the evolutionary history of organisms” • -Russian-American geneticist Theodosius Dobzhansky
Domains of Life: Carl Woese (1977)
Moving Beyond Coacervates- The First Cell:Enclosed self-replicating RNA in membrane
Prokaryotic Cells- Archaea & Bacteria
• Ancient, diverse, abundant, ubiquitous, small size, motile• Extremophiles (“extreme-lovers”):
live in high-salt, high-temperature, low-temp, or high-pressure habitats • Inform origin of life research• Used as a model organism in search
for extraterrestrial life-likely that first life forms lived at high temperatures and high in anoxic environments (no oxygen)
Thermal Hot Springs, Yellowstone National Park
Commercial applications (Taq polymerase- enzyme isolated from Thermus aquaticus bacteria in hot springs, Yellowstone National Park
The First Eukaryotic Cells• Evolved 2.7 billion years ago• Larger and more complex than bacteria, Have a nucleus, complex
organelles, cytoskeleton
Origin of Mitochondria and Chloroplasts
• Chloroplasts evolved from cyanobacteria (+ photosynthesis)• Mitochondria evolved from aerobic bacteria (+ cellular respiration to
make ATP)• + = advantage
Evidence• Membranes- Have double cell
membranes• DNA- Have circular DNA, like
bacterial genome• Reproduction- via budding,
just like bacteria• Size- similar size to bacteria
( 1-10 microns)
Advantages of Multicellularity• Cell specialization, larger size, more complexity• Volvox algae with division of labor-with two cell functions: swimming (somatic
cells) & reproduction (gonidium)
What Makes a World Habitable?
• Temperature• Water• Atmosphere• Energy• Nutrients
Case Study: Protists • Unicellular, diverse• Abundant in water, motile
• Medically important• 1845 Irish Potato Famine- protist Phytophthora infestans• Malaria parasite- Plasmodium • Toxin producing algal blooms- Dinoflagellates
• Ecologically important (primary producers)• Critical to understanding evolution of plants, fungi, animals
Case Study: Protists Plant-like: Euglena Animal-like: Ameoba