Early evolution of life on Earth Wachtershauser. Miller and Urey experiment.
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Transcript of Early evolution of life on Earth Wachtershauser. Miller and Urey experiment.
![Page 1: Early evolution of life on Earth Wachtershauser. Miller and Urey experiment.](https://reader033.fdocuments.in/reader033/viewer/2022061612/56649d0a5503460f949dc292/html5/thumbnails/1.jpg)
Early evolution of life on Earth
Wachtershauser
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Miller and Urey experiment
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Early catabolism
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Evolution of cell types
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Primitive Metabolism
• Early catabolism must make use of chemical disequilibria
• Later, photosynthetic energetics may have evolved– First photosynthetics were undoubtedly anaerobic
photosynthetic bacteria
– Later, oxygenic photosynthesis changed the chemistry of the Earth
• In addition to O2 being an electron acceptor for respiration, it caused development of an O3 layer
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Summary
First evidence for potential life 3.8 billion yrs ago
• other fossil evidence • molecular fossils • chemolithotrophy vs heterotrophs, who
came first? • anoxygenic photosynthesis • oxygenic photosynthesis • Banded iron formations (BIFs)-red beds
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Evolution of cell types
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Endosymbiosis
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Taxonomy
• Until recently, life on Earth in 5 kingdoms:– Bacteria
– Fungi
– Protists
– Plants
– Animals
• Division between Bacteria, Archaea, and Eukarya more profound than former kingdoms: level called domains
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Taxonomic Ranks
• Empire or Domain• Kingdoms (Bacteria and Eukarya not yet divided
into kingdoms)• Phylum• Class• Order• Family• Genus• Species (name is binomial: genus + epithet)
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Bacterial Taxonomy
• Bacterial species is the base unit for taxonomy– Definition of any given species is subjective– >70% sequence similarity of genome– >98% sequence similarity of rRNA– Each species is phenotypically distinct
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Evolutionary Chronometers
• Phenotypic characteristics
• Mole percent Guanine + Cytosine
• DNA sequence similarity (gross sequence similarity)– Good at the species level
• Small-subunit RNA (16S rRNA of prokaryotes; 18S of eukaryotes)
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Phenotypic Taxonomies• Phenotype determination is classic taxonomic
method• Today more reliance on molecular methods for
taxonomies above the genus level– Still, phenotypic differentiation is considered
requirement for separation of species
• Some methods collect large amounts of phenotypic data quickly– FAME analysis– Pyrolysis/GC– Automated testing of enzymatic activities
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Range of G+C contents
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DNA hybridization
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16S rRNA as evolutionary chronometer
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Evolution of sequences
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Evolutionary distance and correction for back- or multiple mutations
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Generation of evolutionary trees
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Molecular microbial ecology
• Signature sequences identify phylogenetic groups– 16S & 18S sequences identify Bacteria, Archaea, and Eucarya
• Probes can be developed for FISH (fluorescent in situ hybridization)
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Community analysis by molecular methods