1. Chapter 22The Origin of Eukaryotes

2. Quick Review Prokaryotes Simple Lack nucleus or any membrane enclosed organelles Eukaryotes Complex Contain nucleus and membrane enclosed organelles

3. 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

4. Question #1

5. 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

6. 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

7. 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

8. Symbiosis & Endosymbiosis

9. 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

10. 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

11. 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

13. 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