Evolution of Eukaryotic Cells

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Evolution of Eukaryotic Cells

• Starting from Prokaryotic Cells!

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Three Prokaryotic Cells
nucleoid nucleoid nucleoid
70S ribosomes 70S ribosomes 80S ribosomes
Krebs Cycle Calvin Cycle Glycolysis Fermentation
ETS Ox Phos Light Reactions Photo Phos Endomembrane System
Cell Membrane Cell Membrane Cell Membrane
Murein Wall Murein Wall None (Contractile Vacuole)
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Three Prokaryotic Cells
Typical Bacterial Cell Murein Wall Naked Circular
DNA genome 70S Ribosomes Carries out Aerobic
Respiration Enzymatic Glycolysis and Krebs Cycle
in Cytosol Electronic ETS and Ox Phos in/across
Mesosomes Highly efficient ATP production from
simple fuel molecules 36 ATP per glucose
nucleoid
70S ribosomes
Krebs Cycle
ETS Ox Phos
Cell Membrane
Murein Wall
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Three Prokaryotic Cells
Typical Cyanobacterial Cell Murein Wall Naked
Circular DNA genome 70S Ribosomes Carries out
Photosynthesis Enzymatic Calvin Cycle and
Condensation Reactions in Cytosol Electronic
Light Reactions and Photo Phos in/across
Thylakoid Membranes Highly efficient ATP
production Highly efficient synthesis of a wide
range of organic molecules from CO2
nucleoid
70S ribosomes
Calvin Cycle
Light Reactions Photo Phos
Cell Membrane
Murein Wall
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Three Prokaryotic Cells
Archaeon Cell No Wall (Contractile Vacuole avoids
burst) Multiple protein-bound DNA molecules in
genome 70S becoming 80S Ribosomes Metabolism by
Fermentation Only Enzymatic Glycolysis and
Fermentation Reactions in Cytosol Comparatively
inefficient ATP production 2 ATP per
glucose Must consume huge amounts of fuel Highly
evolved endocytosis (phagocytosis)--leading to
endosymbiosis Large cytoplasm requires highly
developed endomembrane system from
mesosomes Formation of nuclear envelope to avoid
digesting its own DNA Transposon system for
acquiring/incorporating more DNA into genome
nucleoid
80S ribosomes
Glycolysis Fermentation
Endomembrane System
Cell Membrane
None (Contractile Vacuole)
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Three Prokaryotic Cells
Wall Loss Critical Gene Movement
Endocytosis
Binary Fission of Organelle
Many critical genes moved into the host
nucleoid/nucleus The endosymbiont has become an
organelle ...no longer capable of independent
respiration The mitochondrion has two bounding
membranes The host vesicle membrane The
endosymbiont cell membrane
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Three Prokaryotic Cells
Wall Loss Critical Gene Movement
Binary Fission of Organelle
Endocytosis
A critical gene moved into the host
nucleoid/nucleus is the rubisco small subunit The
endosymbiont has become an organelle ...no longer
capable of independent photosynthesis The
chloroplast has two bounding membranes host
vesicle membrane and endosymbiont cell membrane
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Three Prokaryotic Cells
The fermentation-only archaeon has taken in a
bacterial cell and a cyanobacterial cell as
endosymbionts By not digesting them completely,
but removing the cell wall, the archaeon has
gained two gigantic biochemical pathways
respiration and photosynthesis By moving critical
genes from each endosymbiont, using its
transposon feature, the archaeon has trapped both
endosymbionts as permanent organelles This is
almost a eukaryotic plant cell!
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Three Prokaryotic Cells
The archaeon still needs to convert its
endomembrane system into endoplasmic
reticulum And consolidate the encircling
membranes into a nuclear envelope And make its
circular chromosomes linear with telomeres And
finish the evolution of the 80S ribosomes It also
needs to entrap some spirochetes for a
cytoskeleton and for a eukaryotic flagellum The
sequence of these steps relative to the
endosymbiont capture is still being resolved!