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Evolution of Eukaryotic Cells Starting from Prokaryotic Cells!

Three Prokaryotic Cells nucleoid 70S ribosomes ~80S ribosomes Krebs CycleCalvin CycleGlycolysis + Fermentation ETS + Ox PhosLight Reactions + Photo PhosEndomembrane System Cell Membrane Peptidoglycan Wall None (Contractile Vacuole)

Three Prokaryotic Cells nucleoid 70S ribosomes Krebs Cycle ETS + Ox Phos Cell Membrane Peptidoglycan Wall 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

Three Prokaryotic Cells nucleoid 70S ribosomes Calvin Cycle Light Reactions + Photo Phos Cell Membrane Peptidoglycan Wall 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 CO 2

Three Prokaryotic Cells nucleoid ~80S ribosomes Glycolysis + Fermentation Endomembrane System Cell Membrane None (Contractile Vacuole) 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

Three Prokaryotic Cells Binary Fission of Organelle Endocytosis Wall Loss Critical Gene Movement 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

Three Prokaryotic Cells Binary Fission of Organelle Endocytosis Wall Loss Critical 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 photosynthesis The chloroplast has two bounding membranes host vesicle membrane and endosymbiont cell membrane

One Prokaryotic Cell 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!

One Prokaryotic Cell—finishing up! 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 genomic 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!