Overview of Eukaryotes

Overview of Eukaryotes

Ecological relationships

• Symbiotic Relationship: two species living together in a close and long term biological interaction
• "Syn" = together
• Many prokaryotes are endosymbiotic: living within another organism
• Mutualism: Both species benefit
• Commensalism: one species benefits while the other is unaffected
• Competition: Both species are negatively affected
• Predation / parasitism: One species benefits, the other is negatively affected

Oxygen Revolution

• Cyanobacteria use photosynthesis and produce oxygen
• Oxygen accumulates in the earth atmosphere
• Oxygen was toxic to most early taxa
• Obligate anaerobes: intolerant of oxygen
• Took refuge in anaerobic environments
• Examples: Rotting substrates, animal guts
• Others adapted and began aerobic respiration
• Using oxygen to convert fuel into energy

Diversification of Eukaryotes

• 3.5 BYA Cyanobacteria began producing oxygen with photosynthesis
• 2 BYA Eukaryotes evolved and began using the oxygen
• Novel environment fueled diversification
• Metabolism changed from anaerobic to aerobic
• Led to more complex and diverse cells
• Membrane enclosed organelles appeared

Eukaryotic Features

• Linear DNA
• Membrane bound nucleus
• Membrane bound organelles
• Examples: Mitochondria and Chloroplasts
• Larger size than Prokaryotes
• Cytoskeleton evolved to produce more complex morphology

Origin of Eukaryotic Cells

• Infolding of cell membrane
• Created structures in the cell Examples: Endoplasmic Reticulum, Nuclear Envelope
• Endosymbiotic Theory
• A cell absorbed an endosymbiotic aerobic heterotrophic prokaryote
• likely an Archaea
• Enabled cells to produce energy from oxygen and organic matter
• Would eventually become mitochondria

• Photosynthetic Endosymbiosis
• Other cells absorbed different prokaryotes
• Likely Cyanobacteria, enabling these lineages to use photosynthesis to produce energy
• Would become chloroplasts
• Evidence for Endosymbiosis Theory
• Both Mitochondria and Chloroplasts
• Self replicate through binary fission
• Does not require DNA of the host cell
• Their DNA is circular (like prokaryotes)
• Similar size and structure to bacteria
• Contain 2 layers of cell membrane
• inner membrane is the prokaryotes original outer membrane
• outer membrane is from the host cell when it was being engulfed