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Chapter 22 The Origin of Eukaryotes
Chapter 22The Origin of Eukaryotes<br />
Quick Review<br />Prokaryotes<br />Simple<br />Lack nucleus or any membrane enclosed organelles<br />Eukaryotes<br />Complex<br />Contain nucleus and membrane enclosed organelles<br />
Origin of Eukaryotes<br />Arose during the Proterozic eon<br />Not fully understood how first cell originated<br />DNA sequences examined<br />Studies show that nuclear, mitochondrial and chloroplast genomes are derived from cells that were once separate but then came together<br />All eukaryotes contain DNA in nucleus and mitochondria<br />Plants have DNA in chloroplasts as well<br />
Origin of Nuclear Genome<br />Derived from ancient bacteria and archea<br />Bacteria<br />Lipid biosynthesis and genes encoding proteins for metabolic pathways<br />Archea<br />Genes related to transcription and translation<br />Possibilities for relationship between bacteria and archea<br />Symbiotic<br />Endosymbiotic<br />
Symbiosis<br />2 different species live in direct contact with each other<br />Hypothesis<br />Ancient bacterium and archaeon formed a symbiotic relationship<br />A fusion event combined the genetic material of the organisms<br />Natural selection favored retention of genes involved with translation and transcription, metabolism and lipid biosynthesis<br />
Endosymbiosis<br />Relationship in which a smaller organism (endosymbiont) lives within a larger organism (host)<br />Hypothesis<br />An ancient archeon engulfed a small bacterium into its cytoplasm<br />Possibly occurred via endocytosis<br />Eventually genes were transferred from the bacterium to the host archeon resulting in the nuclear genome<br />
Origin of Mitochondrial and Chloroplast Genomes<br />Russian botanist suggested an endosymbiotic origin<br />Discovery of genetic material in chloroplasts and mitchondria supported this theory<br />Mitochondria in eukaryotes likely derived from bacterial species similar to a-proteobacteria<br />Bacteria that utilizes oxidative phosphorylation to make ATP<br />
Mitochondrial and Chloroplast Genomes, cont.<br />2 possible hypotheses<br />An endosymbiotic event involving an a-proteobacteria resulted in the first eukaryotic cell and the first mitochondrian was a by-product<br />OR<br /> A symbiotic or endosymbiotic event produced the first eukaryote, and then a subsequent endosymbiosis produced the first mitochondria<br />
DNA Sequencing<br />DNA sequencing of mitochondrial and prokaryotic genomes has been used to determine which hypothesis is correct<br />Data from DNA sequencing has indicated that chloroplasts originate from an endosymbiotic event between a eukaryote and a cyanobacterium<br />
IS IT POSSIBLE?<br />In 2001, an endosymbiotic relationship between two different proteobacteria was reported<br />Mealybugs<br />Bacteria survive within cytoplasm of large host cells of bacteriome<br />Due to this observation, it is now known that endosymbiosis can occur between two different prokaryotic species<br />