4 Origin of Prokaryotes and Eukaryotes Flashcards
What is the evidence for prokaryotic life?
Suitable age rocks contain three types of fossil evidence:
1) Fossil stromatolites - covered in cyanobacteria
2) Fossil microorganisms - silicified in cherts; acritarchs (resistant cell walls) preserved in siltstone
3) Carbonaceous matter identified chemically as product of ancient life - organic or inorganic formation
What is the importance of rubisco relating to ancient life?
Rubisco selectively takes in Carbon-12 - this allows for life to occur
When did prokaryotes evolve?
Very early - remain relatively unchanged to the present day
What are the two communities of advanced prokaryotic life in the oceans by 3500Mya?
Complex and diverse stromatolites on the floors of shallow seas
Free living prokaryotes floating around in the oceans (anaerobic)
What do the both communities of advanced prokaryotic life contain?
Autotrophic cyanobacteria - produce O2 as biproduct of photosynthetic metabolism
Heterotrophic consumers - sweep up waste products
What were the early oxygen sinks?
1) Volcanic gases comprising early atmosphere readily combine with O2 - forms –NO, NO2, H–H2O, CH4–CO2 etc
2) Dissolved iron - scavenged O2 to form BIFs
3) Aerobic respiration of microorganisms - would switch back to anaerobic fermentation when O2 in short supply
What are BIFs?
Banded iron formations
- Chemical sediment containing stores of iron
Where did the evidence for early oxygen sinks comes from?
BIFs
Pyritic conglomerates - iron pyrite pebbles indicating no O2 in atmosphere
Red beds - O2 in atmosphere needed to oxidise the iron
- Indicates a massive switch from an anaerobic to an aerobic world
What was ‘The Great Oxygenation Event’?
2.4-1.8 Mya
The environment becomes aerobic
Coincides with the Huronian Ice Age caused by elimination of atmospheric methane during the GOE
What do we have to consider with the origin of eukaryotes?
When were conditions suitable - can’t have evolved until after GOE
Fossil evidence for eukaryotes
What are the theories of how the eukaryotic cell originated?
1) Symbiosis
- Proto-eukaryote engulfs Thermoplasma-like Archaebacterium (containing DNA material)
2) Elaboration of cell membrane
- Cell membrane folds in on itself and separates off DNA material, forming nucleus
3) Multiple symbiotic events
- Different parts of cells formed in these events when Earth switched from anaerobic to aerobic
What is the symbiotic origin of mitochondria?
Facultative aerobe-proteobacterium
- Alpha subdivision of the purple non-sulphurs
- Mitochondria are very similar to these
What is the symbiotic origin of chloroplasts?
Closest to Cyanobacteria
Chloroplasts:
- Able to separate off when cell divides
- Have own DNA
- In anything that photosynthesises
What is the symbiotic origin of flagella and cilia?
Spirochaete bacteria
- Basal body sunk into the cell wall - divides when the cell divides - potentially contains RNA
What is the potential symbiotic origin of mitosis?
Centriole spindles are equivalent to tubules in cilia/flagella spirochaete bacterium
- Less evidence to prove this
What is the idea of circular phylogeny?
Bacteria and Archaea react symbiotically to form eukaryotes
