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Lecture 4

BIOL215 Lecture 4 Notes.pdf

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Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 4 Notes The consequences of O p2oduction includes: • Allowed for the evolution of a new type of metabolism - aerobic metabolism: greater energy yield per mol of C substrate consumed 2- • Changed ocean chemistry: S and N oxidation (SO 4 collects in ocean) • Allowed for the formation of the ozone layer - O protection from UV 3 • Poisoned environment - anaerobic organisms became confined to refuge habitats • Organisms had to evolve mechanisms to detoxify the noxious by-products of O -2superoxide, hydrogen peroxide... • The release of O2by photosynthesis is perhaps the single most significant effect of life on the geochemistry of the Earth In Phanerozoic period, the increased fluctuation of oxygen in the environment allowed for the evolution of larger animals Origins of Eucaryotes: • Cells existing prior to 1.8 (2.7) bya were all prokaryotes: bacteria and archaea • Eukaryotes appear in the fossil record ca. 1.8 bya • Chemical markers (steranes) produced only by eukaryotes are detected in rocks (roughly 2.7 bya) • How did eucaryotes differ? • Prokaryotes have no nucleus, organelles, or microtubules and have 70S ribosomes. They have an outer cell wall composed of peptidoglycan (bacteria, but not archaea). They are generally small, <2 micrometer in diameter • Eukaryotes were much larger (100-1000x larger in size), have a nucleus, have lots of organelles and microtubules. Endosymbiotic theory of origin of eucaryotes: • Theory proposed by Lynn Marguilis • Mitochondria and chloroplasts of eucaryotes were at one time free-living bacteria that were engulfed by an archaea and evolved an obligatory symbiosis (a relationship between two organisms that benefits both) • Mitochondria - proteobacterium Chloroplast - cyanobacaterium • • Theory very strongly supported by data • Theory believed that host archaeon with membranes, cytoskeleton, and a nucleus then engulfed either a proteobacterium or cyanobacterium Evidence for endosymbiotic theory: • Organelles (chloroplasts and mitochondria): 1. Contain own DNA, similar to bacterial DNA, no histones, circular 2. Are surrounded by a double membrane - the inner one looks like a bacterial membrane 3. Show antibiotic sensitivity (use antibiotics and show that you can inhibit their replication like with bacteria) 4. Have ribosomes (70S) like bacteria (eukaryotes have 80S) Secondary endosymbiosis: In 2 groups of protists, we can still see the evidence of a second endosymbiotic event. The • nucleomorph: a remnant of the nucleus of the endosymbiotic in the chloroplast! Biodiversity I Method for organizing information • Grouping similar organisms together • Historically, it involved grouping organisms into different categories based on their physical characteristics (hard for microbes) Ideally it should reflect the evolutionary distances and relationships among organisms • Predict characteristics of newly described organisms • Understand the history of life Difficulty in classifying microorganisms: • Morphologically simple - they have fewer obvious features that can be used to measure relatedness of species • RNA proposed because it is found in all organisms • Transmission of genetic information captures ancestral relationships • Slowly changing • Large enough to record useful information on evolutionary change Two kingdoms of organisms: • Created by Aristotle • Plantae and Animalia • 20th Century • Single-celled organisms (prokaryotes) and single and multicellular organisms (eukaryotes) • Problem with two kingdoms became five • Prokaryotes are NOT monophyletic (a group of organisms that contains all its descendants and its ancestor) branches of the tree of life; they are two separate lineages that evolved similar character states (polyphyletic) • Five kingdoms, one for prokaryotes and four (protists, fungi, plants, and animals) to cover eukaryotes Molecular phylogeny: • RNA sequence analysis identifies 3 major lineages (called domains) (Carl Woese 1977): • Bacteria (prokaryote) • Archaea (prokaryote) • Eucarya (eukaryote) Classification within each domain is based on rRNA or more recently using a number of different • genes Horizontal gene transfer and the tree of life: • What if the genes were not only transferred vertically from parent to offspring (ancestor to descendent)? • During endosymbiosis genes transferred from the endosymbiont to the host genome (EGT) plus EGR (Endosymbiotic gene replacement) •HGT is also effected by a virus or a small, circular DNA particle known as a plasmid that contains a foreign gene that can be transferred • 20% of the E. coli genome can be traced to HGT • 1/3 of the genome of some prokaryotic organisms has been acquired through HGT Archaea: •Archaea are hypothesized hosts that evolved with bact
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