Early Earth and the origin of life.
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Physical conditions on the early earth differed significantly from today, especially in the lack of atmospheric oxygen -
Organic molecules can form spontaneously under such conditions with energy input -
Several steps important to life have been demonstrated to self-organize in the laboratory, such as the catalysis of reactions, creation of internal environments, and the formation of protobionts -
RNA might have served as the earliest genetic material and enzymes (ribozymes)
Prokaryotes (=Monera) represent the simplest life forms, and fossils indicate they were the earliest living things.
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They lack membrane-bound organelles, and elements of their ribosomes function differently -
They have structures athat are either unique or are constructed in a unique way (pili, endospores, capsules, cell walls)
They can be characterized by their shapes (coccus, bacillus or spirillum), reactions to dyes (e.g. Gram stain) and colony shape and color or molecular tools.
They obtain nutrition a variety of ways: (chemo- and, photo-autotrophic and, heterotrophic) -
Two domains: Bacteria and Archaea; -
Archaea are simpler, but show molecular homologies with eukaryotes; mostly extreme environments (thermophiles, halophiles) -
Bacteria are important in food chains, as disease organisms (and potential biological weapons), or environmental remediation -
Know differences between Bacteria and Archaea (16.8)!
Eukaryotes have true organelles
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The eukaryotic cell probably originated as a community of prokaryotes (mitochondria and chloroplasts from symbiotes) -
The simplist groups of eukayotes are termed "Protists", but this is probably a polyphyletic group -
Three main divisions based on feeding and size: Protozoa (single-celled heterotrophs), Algae (single-celled autotrophs) and Seaweeds (multi-celled autotrophs)
Multicellular life likely evolved from colonial protists
- True multicellularity requires specialization of cells, interdependence and coordination
- multicellular life evolved from colonial protists several times independently
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