CMMB 343 Lecture 4: History and Diversity — Part 4
19 Jan 2019
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History and Diversity — Part 4
ENDOSYMBIOTIC ORIGIN OF EUKARYOTES
- Endosymbiosis
- Well-supported hypothesis for origin of eukaryotic cells
- Contends that mitochondria and chloroplasts arose from symbiotic association of prokaryotes
within another type of cell
- There was some type of archaean like organism that started to swallow smaller bacteria, to
make a cell with organelles — similar thing happened with chloroplasts
- Cyanobacterium swallowed by eukaryotes in chloroplasts
- Cyanobacterium are the ancestors of chloroplasts
- This happened 1.8 billion years ago
- Two hypotheses differ slightly in the history of the symbioses, but the fundamental idea is the
same
- The key point is that we have something on the eukaryotic branch that swallows an H2-
producing bacterium which becomes mitochondria. Then it swallows a cyanobacterium to
become a chloroplast
- Somewhere in there, the organism also got a membrane-bound nucleus, although we don't
know how this happened yet
ENDOSYMBIOTIC ORIGIN OF EUKARYOTES
- Both hypotheses suggest eukaryotic cell is chimeric
- Mother cell (eukaryotic) started to engulf another cell (Bacteria)
- This is supported by several features
- Eukaryotes have lipids and energy metabolisms similar to those of Bacteria
- Energy metabolism is a property of the mitochondria (originally bacteria) that was
swallowed
- Eukaryotes have transcription and translational machinery most similar to those of Archaea
- DNA processing method not affected by endosymbiosis
- Looks like archaeal DNA processing
- Mitochondria and chloroplasts contain their own genomes (circular, like prokaryotes) that
contain bacterial SSU rRNA (16S rRNA) genes
- Mitochondria and chloroplasts have small circular genomes, which are remnants of the
original bacteria that were swallowed
- These genome still have their own 16S rRNA
- When genes of mitochondria are sequenced, see that ancestor was proteobacterium for
mitochondria
- Chloroplasts were originally cyanobacteria
- Microbes evolved many different ways to do photosynthesis
DIVERSITY OF BACTERIA
- Contains at least 80 major evolutionary groups (phyla)- possibly as many as 1500
- More than 90% of characterized genera and species come from four phyla
find more resources at oneclass.com
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Document Summary
Well-supported hypothesis for origin of eukaryotic cells. Contends that mitochondria and chloroplasts arose from symbiotic association of prokaryotes within another type of cell. There was some type of archaean like organism that started to swallow smaller bacteria, to make a cell with organelles similar thing happened with chloroplasts. Two hypotheses differ slightly in the history of the symbioses, but the fundamental idea is the same. The key point is that we have something on the eukaryotic branch that swallows an h2- producing bacterium which becomes mitochondria. Then it swallows a cyanobacterium to become a chloroplast. Somewhere in there, the organism also got a membrane-bound nucleus, although we don"t know how this happened yet. Both hypotheses suggest eukaryotic cell is chimeric. Mother cell (eukaryotic) started to engulf another cell (bacteria) Eukaryotes have lipids and energy metabolisms similar to those of bacteria. Energy metabolism is a property of the mitochondria (originally bacteria) that was swallowed.
