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Lecture 10

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Biology 1002B
Tom Haffie

Lecture 10: Evolution of Eukaryotes  Evolution of Eukaryotes o Eukaryotes have more morphology within the domain o Why is there a lot of morphology complexity? o Bacteria and Archaea are unicellular, and eukaryotes are multicellular  The paradox o All morphologically complex life is eukaryotic o All eukaryotes share common complex traits  Nucleus, trafficking, sex, phagocytosis, organelles, cytoskeleton o Prokaryotic cells show no tendency  They don’t have any of the “cool” stuff in the eukaryotes o Why don’t they if evolution is stepwise?  What drove the evolution of eukaryotes? o Oxygen is the key, something changed 2 bya o Earliest bacteria were anaerobic  They get there ATP from glycolysis; fermentation o 2.2 billion years ago cyanobacteria appeared, prokaryotes  They do oxygenic photosynthesis  They release oxygen, they have PS2 and PS1, similar to the chloroplast  Gave rise to oxygen in the atmosphere o Bacteria that undergo aerobic respiration  Now have a lot of oxygen and it can be used as terminal electron acceptor in respiration  With CAC and oxidative phosphorylation generates way more ATP than glycolysis, for the same amount of input substrates  Oxidative phosphorylation in bacteria o Prokaryotes are very small, much smaller than eukaryotes o The protons are pumped out of the cell, and when the protons follows back into the bacteria, it generates ATP o They have their ETC and ATP synthase on their plasma membrane (oxidative phosphorylation) o As the cell gets bigger, the surface area goes up, up volume will increase way faster than the surface area  More volume, more proteins, more organelles in cell, need more energy to support them o The surface area of the plasma membrane is providing the energy, for the cell o The surface area is the constraint that limit the size of the bacteria cells  SA = 4 pi r ^2 V = 4/3 pi r ^3 o Thus the volume cannot get as big because it will not have enough energy to support it because lack of surface area compared with the volume. Thus the bacteria are small o Need to maintain a high plasma membrane surface area/volume  Eukaryotes have (much) bigger genomes o Eukaryotes have 500 – millions times bigger than prokaryotes o The range of genome size in eukaryotes are way bigger than the range of genome size in prokaryotes o Eukaryotes have more energy (ATP) to support a larger genome o Prokaryotes, energy are constricted, so that the genome might be constantly regulated  Must maintain high PM SA/V  Eukaryotic cells –more energy! o The smaller the sphere, the ratio of surface area to volume is much higher o Eukaryotes are fine with low plasma membrane surface area/volume  They can do this because they have mitochondria  A typical human liver cell have about two thousand mitochondria  The membrane surface area of mitochondria is gigantic o In prokaryotes, getting enough energy is a problem, and eukaryotes can get enough energy, energy is sufficient in eukaryotes than prokaryotes o Eukaryotes can support a Larger genome, more genes, more protein coding genes, eukaryotes can support more protein  Endergonic process of protein synthesis takes about 75% of cell’s energy; very energy hungry, thus prokaryotes cannot support as much as eukaryotes o Eukaryotes have more protein diversity than prokaryotes o The thing that constraints bacteria size is energy, their plasma membrane that generates energy, so that they can’t get bigger because the ratio will be lower and not enough energy can be generated and they’ll die o Eukaryotes have a lot more ribosomes than prokaryotes  Endosymbiosis o Ancestral bacterium -> infolding plasma membrane -> nuclear envelope and endoplasmic reticulum ->  Nuclear envelope can control transcription and translation because they’re not in the same place; better control when we can separate the two o Through phagocytosis the cell brings in aerobic bacterium o Cyanobacterium was engulfe
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