-
Origin
- Arose 2.0 - 1.9 BYA
- Eukaryotes came after:
- - the rise of atmospheric oxygen
- - the invention of respiratory metabolism in Bacteria
- - the development of enzymes such as superoxide dimutase, which detoxifies oxygen radicals generated as a by-product of aerobic repsiration
- Oldest known microfossil is ~2billion years old
- Fossils of increasing complexity are evdident from 1.9 to 1.4 BYA
-
Characteristics
- Contain a membrande-enclosed nucleus, mitochondria, chloroplats (phototrophs), Golgi complex, peroxisomes, lysosomes, endoplasmic reticula, micotubules, and microfilaments
- Includes: protists, fungi, unicellular red algae, and unicellular green algae
-
Mitochondrian
- Repsiratory organelle of aerobic Eukarya
- site of respiratory enzymes and oxidative phosphorlyation
- Cristae- internal membranes, sites of enzymes for respiration and ATP synthesis
- Matrix- enzymes for oxidation of organic compounds
- Evolutionary origin- falcutatively aerobic Alphaproteobacterium ~2BYA
-
Chloroplast
- Organelle of photosynthesis in phototrophic Eukarya
- Stroma- lumen of chloroplast, site of enzymes of the Calvin cycle
- Thylakoids- flattened membrane discs, site of chlorophyll and other components involved in capturing light engergy
- Evolutionary origin- a cyanobacterium ~1.5BYA
-
Endosymbiotic theory
- 1. Mitochondria and chloroplasts have DNA for rRNAs, tRNAs, and respiration/photosynthesis
- 2. Eukaryotic nucleus contains bacterial genes derived from mt and chl
- 3. Mt and chl have their own ribosomes with 70S size like in Bacteria
- 4. Antibiotics that kill or inhibit Bacterial 70S ribosome function also interfere with protein synthesis in mt and chl
- 5. Phlyogenetic analysis based on 16S rRNA gene sequencing places mt and chl in domain Bacteria
-
Hydrogensomes
- Certain Eukarya thought to lack mitochondria have been found to have hydrogensomes
- Found in obligate or aerotolerant anaerobes (in anaerobic Eukarya)
- Lack enzymes of the citric acid cycle, usually lack cristae, and oxidizes pyruvate to acetate, H2 and CO2
- Allows ATP to be made by SLP
- Contain DNA and ribosomes and functions as a fermentive organelle
- Metabolically degenerate mitochondria
-
Mitosomes
- Relic mitochondria
- Found in some eukaryotes that lack mitochondria and hydrogensomes
- Clustered mitochondria-like proteins surrounded by tiny double membrane sacs
- Derived from mitochondria, but even more degenerate than hydrogensomes
-
New Hypothesis
- 1. Aquisition of the mitochondrian led to the origin and massive evolutionary radiation of Eukarya
- 2. Later aquistion of the chloroplast by one of the Eukarya lineages resulted in phototrophic eukaryotes
-
Nucleus Hypothesis
A nucleus bearing cell spontaneously arose from an early kind of cell before the divergence of Bacteria and Archaea in response to teh increasing genome size of the early eukaryote
-
Hydrogen Hypothesis
A hydrogen-dependent host aquired a facultatively aerobic symbiont
-
Chimeric Nature of Eukaryotic Cell
- SSU rRNA gene sequence is mor similar to Archaea than Bacteria
- Transcription/translation apparatus has many similarities to Archaea
- Lipids are ester-linked like Bacteria
- Energy metabolism is mor similar to Bacteria
|
|