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Evolution of Eukaryotes

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Western University
Biology 1002B
Tom Haffie

Evolution of Eukaryotes  Formation of Endomembrane System o Ancient prokaryotic cell o Through gradual in-folding of plasma membrane o Endomembrane system formed  Golgi apparatus  ER  Nuclear envelope  Energy-Transducing Organelles o Endosymbiosis  Prokaryotic ancestors of mitochondria and chloroplasts were engulfed by larger prokaryotic cells  Formed mutually advantageous relationship – symbiosis  Mitochondria came first - capable of using oxygen for aerobic respiration  Chloroplasts developed from ingested cyanobacteria o Theory Evidence  Morphology  Form or shape of both organelles is similar to prokaryotic cells  Reproduction  Mitochondria or chloroplasts are derived only from preexisting mitochondria and chloroplasts – divide by binary fission  Genetic Information  Both organelles contain their own DNA – codes for the proteins essential for the organelles function  Transcription & Translation  Contain a complete transcription and translational machinery – enzymes and ribosomes  Similar ribosomes to prokaryotic cells  Electron Transport  Can generate energy in the form of ATP through their own ETC Driving Evolution of Eukaryotes  Earliest prokaryotes were anaerobic  2.2 bya cyanobacteria evolve o Oxygenic photosynthesis o Atmosphere contains oxygen  Oxygen as terminal electron acceptor o Prokaryotes that undergo aerobic respiration  Oxygenic Phosphorylation o More ATP Eukaryotic Cells Are Bigger & More Complex  Endosymbiosis  cells overcame energy barrier  Prokaryotic cells made enormous amounts of ATP through mitochondrion  Prokaryotes o High plasma membrane surface area to support volume of cell  Energy supplied by plasma membrane supports volume of cell  Transporters also need enormous PM o Don't have a lot of energy  Make less protein  Eukaryotes o Low plasma membrane surface area to volume ratio o ETC is in mitochondrion membrane o More ATP = greater function o Complexity  Processes (Proteins are linked to function)  Tissue development  Multicellularity  Endomembrane system  Energy Required  Maintaining DNA & DNA replication o 2% of cell energy budget  Protein Synthesis o 75% of cell energy budget o Lots of ATP = lots of protein = greater function & bigger genome (genes code protein) Lateral Gene Transfer  Million years after endosymbiosis  Lots genes in both mitochondria and nucleus  Lateral Gene Transfer o Some genes in chloroplastic genome and mitochondrion genome have relocated into nucleus  Ex. Southern Blot (see picture) o Species B – lateral gene transfer has occurred o Species C – lateral gene transfer is occurring o Species A – lateral gene transfer has not occurred Earliest Eukaryotes  Diplomonads o Very primitive eukaryotes o Contains nucleus but lack mitochondria o Question: did it have them and then lost them or did it not
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