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Unformatted text preview: 3/16/11 1 Lecture 28: Friday March 18, 2011 Biology 171 Origins of Eukaryotes and the Diversity of Protists Announcements Next Week in Discussion: Phylogenies Endosymbiotic Origins of Eukaryotes Protist Diversity - New Molecular Perspectives Photosynthesis & 2ndary Endosymbioses Malaria Milkweed disease Text Reading Chapter 29 (519-543) Bacterial Cell. Eukaryotic Cells represent a quantum leap in size and complexity. When and how did they evolve? Animal Eukaryotic Cell A Lot of Important Stuff Happened During the Proterozoic Eukaryotes evolved about 2.1 billion years ago Multicellular eukaryotes evolved between 1.2 and 1.5 billion YA Diversifcation oF eukaryotes was slow until the end oF snowball earth towards the end oF the Proterozoic Prof. Lynn Margulis (University of Massachusetts, Amherst) In 1967, she proposed an endosymbiotic hypothesis For the origin oF mitochondria : these organelles evolved from free-living bacteria that long ago entered into a symbiosis with ancestral eukaryotes . Similar proposals had previously been made For chloroplasts . She was criticized as a radical, and her scientific work was rejected by mainstream biology for many years. Her work has more recently received widespread support and acclaim and is generally accepted by most scientists Her hypothesis that the current eukaryotic cell arose from a symbiotic union with a primitive bacterial cell has been hailed as one of the great achievements of twentieth-century evolutionary biology Richard Dawkins 3/16/11 2 bacterium bacterium A model of the origin of eukaryotes through serial endosymbiosis. Evolution of Eukarya Do the Data Support the Endosymbiosis Theory? Mitochondria and chloroplasts are about the size of an average bacterium Both organelles replicate by fission, as do bacteria, and have their own ribosomes to manufacture their own proteins Both organelles have double membranes , consistent with the engulfing mechanism Mitochondria and chloroplasts have genes that code for the enzymes needed to replicate and transcribe their own genomes...
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