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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
nucleoid
70S ribosomes
Krebs Cycle
ETS + Ox Phos
Cell Membrane
Murein Wall
Typical Bacterial CellMurein WallNaked Circular DNA genome70S RibosomesCarries out Aerobic RespirationEnzymatic Glycolysis and Krebs Cycle in CytosolElectronic ETS and Ox Phos in/across MesosomesHighly efficient ATP production from simple fuel
molecules36 ATP per glucose
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Three Prokaryotic Cells
nucleoid
70S ribosomes
Calvin Cycle
Light Reactions + Photo Phos
Cell Membrane
Murein Wall
Typical Cyanobacterial CellMurein WallNaked Circular DNA genome70S RibosomesCarries out PhotosynthesisEnzymatic Calvin Cycle and Condensation Reactions in
CytosolElectronic Light Reactions and Photo Phos in/across
Thylakoid MembranesHighly efficient ATP production Highly efficient synthesis of a wide range of organic
molecules from CO2
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Three Prokaryotic Cells
nucleoid
80S ribosomes
Glycolysis + Fermentation
Endomembrane System
Cell Membrane
None (Contractile Vacuole)
Archaeon CellNo Wall (Contractile Vacuole avoids
burst)Multiple protein-bound DNA molecules
in genome70S becoming 80S RibosomesMetabolism by Fermentation OnlyEnzymatic Glycolysis and Fermentation
Reactions in CytosolComparatively inefficient ATP
production 2 ATP per glucoseMust consume huge amounts of fuelHighly 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
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Three Prokaryotic Cells
Binary Fission of Organelle
Endocytosis
Wall LossCritical Gene Movement
Many critical genes moved into the host nucleoid/nucleusThe endosymbiont has become an organelle...no longer capable of independent respirationThe mitochondrion has two bounding membranesThe host vesicle membraneThe endosymbiont cell membrane
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Three Prokaryotic Cells
Binary Fission of Organelle
Endocytosis
Wall LossCritical Gene Movement
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 photosynthesisThe chloroplast has two bounding membraneshost vesicle membrane and endosymbiont cell
membrane
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Three Prokaryotic CellsThe 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 CellsThe 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!