Endosymbiosis & The Origin of Eukaryotic Cells

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