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Chapter 22 The Origin of Eukaryotes
 

Chapter 22 The Origin of Eukaryotes

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Chapter 22 The Origin of Eukaryotes Chapter 22 The Origin of Eukaryotes Presentation Transcript

  • Chapter 22The Origin of Eukaryotes
  • Quick Review
    Prokaryotes
    Simple
    Lack nucleus or any membrane enclosed organelles
    Eukaryotes
    Complex
    Contain nucleus and membrane enclosed organelles
  • Origin of Eukaryotes
    Arose during the Proterozic eon
    Not fully understood how first cell originated
    DNA sequences examined
    Studies show that nuclear, mitochondrial and chloroplast genomes are derived from cells that were once separate but then came together
    All eukaryotes contain DNA in nucleus and mitochondria
    Plants have DNA in chloroplasts as well
  • Question #1
  • Origin of Nuclear Genome
    Derived from ancient bacteria and archea
    Bacteria
    Lipid biosynthesis and genes encoding proteins for metabolic pathways
    Archea
    Genes related to transcription and translation
    Possibilities for relationship between bacteria and archea
    Symbiotic
    Endosymbiotic
  • Symbiosis
    2 different species live in direct contact with each other
    Hypothesis
    Ancient bacterium and archaeon formed a symbiotic relationship
    A fusion event combined the genetic material of the organisms
    Natural selection favored retention of genes involved with translation and transcription, metabolism and lipid biosynthesis
  • Endosymbiosis
    Relationship in which a smaller organism (endosymbiont) lives within a larger organism (host)
    Hypothesis
    An ancient archeon engulfed a small bacterium into its cytoplasm
    Possibly occurred via endocytosis
    Eventually genes were transferred from the bacterium to the host archeon resulting in the nuclear genome
  • Symbiosis & Endosymbiosis
  • Origin of Mitochondrial and Chloroplast Genomes
    Russian botanist suggested an endosymbiotic origin
    Discovery of genetic material in chloroplasts and mitchondria supported this theory
    Mitochondria in eukaryotes likely derived from bacterial species similar to a-proteobacteria
    Bacteria that utilizes oxidative phosphorylation to make ATP
  • Mitochondrial and Chloroplast Genomes, cont.
    2 possible hypotheses
    An endosymbiotic event involving an a-proteobacteria resulted in the first eukaryotic cell and the first mitochondrian was a by-product
    OR
    A symbiotic or endosymbiotic event produced the first eukaryote, and then a subsequent endosymbiosis produced the first mitochondria
  • DNA Sequencing
    DNA sequencing of mitochondrial and prokaryotic genomes has been used to determine which hypothesis is correct
    Data from DNA sequencing has indicated that chloroplasts originate from an endosymbiotic event between a eukaryote and a cyanobacterium
  • IS IT POSSIBLE?
    In 2001, an endosymbiotic relationship between two different proteobacteria was reported
    Mealybugs
    Bacteria survive within cytoplasm of large host cells of bacteriome
    Due to this observation, it is now known that endosymbiosis can occur between two different prokaryotic species