Bis2C.Lecture13.followup

Bis2C.Lecture13.foll - Eukaryotic Plastid Symbioses Follow Up The last universal common ancestor(LUCA was the ancestor to all modern organism LUCA

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Eukaryotic Plastid Symbioses Follow Up
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Archaea Eukaryotes Bacteria LUCA The last universal common ancestor (LUCA) was the ancestor to all modern organism. LUCA was likely a single celled organism which had many features of modern organisms, including a DNA genome, transcription and translation, and a cell membrane (possibly a cell wall too). Here we are drawing just the DNA and the cell membrane and wall. DNA Membrane Cell wall
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Initially, after the eukarya lineage separated from the archaeal lineage, the cells of these organisms resembled those of bacteria and archaea. Archaea Eukaryotes Bacteria LUCA
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N Then some new features evolved in a common ancestor of all eukaryotes. This led to an organism with: A complex cytoskeleton. Loss of a cell wall (if it was present) Phagocytosis A membrane that separated its genome from the rest of the cell.
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N α Proteo This organism then encountered an alpha proteobacteria in its environment. Note - The proteobacteria was surrounded by two membranes (with a cell wall of peptidoglycan in between - as seen in Gram negative bacteria) and had its own genome.
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N This organism was brought into the host cell by phagocytosis α Proteo
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N α Proteo This became an intimate association of some kind (a symbiosis) although it could have initially been any kind of symbiosis (i.e., parasitic, mutualistic, or commensal). Note - Initially, the intracellular bacteria will be surrounded by three membranes and the peptidoglycan cell wall. The red represents the plasma membrane of the host
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N M Eventually, this became a mutualistic symbiosis and both partners (the original host and the alpha proteobacteria) became one organism. Thus what was once a proteobacteria became an organelle of the host. This organelle was the ancestor of the mitochondria. Note - once the symbiosis became a permanent mutualistic association, one of the two bacterial membranes and the cell wall was lost (it kept the host membrane and one bacterial membrane). This was the “primary symbiosis” in the history of mitochondria.
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Note - the evolutionary ancestry of the mitochondria has been traced to alpha proteobacteria using phylogenetic analysis of genes found in mitochondrial genomes
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Note - this organism was the common ancestor of all modern eukaryotes. It gave rise to the major lines of descent within eukaryotes. N M N M N M N M N M N M Archaea Eukarya Bacteria LUCA N M N M N M N M N M N M
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eukaryotic tree from the book. Note - this tree can be inferred from studies of either nuclear genes or mitochondrial genes - after the symbiosis occurred the two genomes follow the general history. N
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Bis2C.Lecture13.foll - Eukaryotic Plastid Symbioses Follow Up The last universal common ancestor(LUCA was the ancestor to all modern organism LUCA

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