Eukaryote SET Flashcards
When did Eukaryotes emerge?
Evidence for Eukaryotes 1.7 billion years ago
What features do prokaryotes have that would support SET?
Prokaryotes live in communities (biofilms) - live in close to each other
Share ‘common goods’. - genes
Lots of opportunities for symbiotic relationships to evolve.
What is the Black Queen Theory?
Prokaryotes can loose genes over time and rely on those produced in the community
They become symbiotic and reliant on the community.
What is endosymbiosis?
Cell lives within another cell, so if there was a situation where cells are in close proximity and have membranes that are flexible, its possible the cell was taken up by another larger cell and then lived within it.
SET step 1
Infolding of the plasma membrane of ancestral prokaryote (probably an archaea).
This could lead to the formation of→ Endoplasmic reticulum, Nuclear envelope, Nucleus.
SET step 2
Ancestral prokaryote engulfed an aerobic heterotrophic Prokaryote
Became the Mitochondrion
The creation of → Ancestral Heterotrophic Eukaryote
SET step 3 (plants)
Ancestral Heterotrophic Eukaryote then engulfed a
Photosynthetic prokaryote (Cyanobacteria)
→ Plastid
Lead to formation of=→ Ancestral Photosynthetic Eukaryote
What is secondary symbiosis?
Evidence chloroplasts of some algae not derived in a 1o endosymbiosis
Engulfed photosynthetic eukaryotes. (eukaryotic cell engulfed another eukaryotic cell)
Vestige of a nucleus - nucleomorph
Evidence for SET
Mitochondria and chloroplast contain DNA that is closed circular like that found in bacteria. – degenerated bacteria
Mitochondrial DNA in the nucleus resembles bacterial gene sequences.
70s ribosomes are found in mitochondria and chloroplasts (Eukaryotic ribosomes are 80s).
Phylogeny of mitochondria RNA fits early endosymbiosis.
What are the main differences between prokaryotic and Eukaryotic cells?
Prokaryotic smaller (Eukaryote 10-100 times bigger)
Prokaryotic cell has nucleoid and plasmids.
Eukaryotic cell has mitochondrion, nuclear membrane, nucleus, endoplasmic reticulum, and Golgi complex.
Eukaryotes differentiate into different types of cells and for multicellular organisms.
Prokaryotes have 70s ribosomes, eukaryote have 80s.
Eukaryotes have membrane bound organelles
Eukaryotes have cytoskeleton and in folding membranes (larger surface area for reactions)
What happened on the planet approximately 2 billion years ago to favour the evolution of the eukaryotic cell?
Increased oxygen levels – cyanobacteria released oxygen
Oxygen best oxidiser - more energy from metabolism, larger cells, complex, multicellular.
Oxygen can form ozone, that can block UV light (UV light can damage DNA, prohibiting life on the surface)
Why do we think the bacteria that later became mitochondria were incorporated into the eukaryotic cell before cyanobacteria that later became chloroplasts?
There are cells with just mitochondria and without chloroplasts.
If chloroplasts came first you would expect all cells to have chloroplasts.
