Wk 7 Lec 1 - C hapte 15 r TheEvolution of Microbial Life...

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Chapter 15 The Evolution of Microbial Life
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PROKARYOTES Theoldest life-forms Remain the most numerous and widespread organisms today Survive in environments too extremefor eukaryotes Despite being small, prokaryotes havean immense impact on life Cause serious illness Have beneficial relationships with other organisms Are essential in the decomposition of dead organisms
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Two Main Branches of Prokaryotic Evolution Bacteria and Archaea arethetwo main branches of prokaryotic evolution Domains Bacteria and Archaea Probably evolved from a common ancestor Differ in nucleotidesequences and other molecular features Peptidoglycan present in bacteria but not archaea Archaea aremore like eukaryotes than like bacteria
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Prokaryote Structure Prokaryotes comein a variety of shapes Prokaryotes may be shaped as Spheres (cocci) Rods (bacilli) Curves or spirals (vibrios, spirilla, spirochetes) Most are unicellular and very small (there are exceptions)
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Prokaryote Structure Various structural features contribute to the success of prokaryotes External structures Cell wall Maintains shape, protects, prevents lysis in hypotonic environment May becovered by a capsulethat aids in protection, adhesion Distinguished as gram positiveor gram negative Pili Help in adhesion to other bacteria or surfaces Provide links during conjugation
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Prokaryote Structure Motility Flagella Enable movement Havea propeller-like structurevery different from eukaryotic flagella Internal organization Simpler than eukaryotic cells in both structureand organization of genome About one-thousandth as much DNA as eukaryote Somehavespecialized membranes that perform metabolic functions
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Prokaryote Reproduction In favorableenvironments can reproduce exponentially very quickly by a process called binary fission Many have adaptations to withstand extreme environments Example: Bacterial endospore
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Nutritional Diversity of Prokaryotes Prokaryotes obtain nourishment in a variety of ways Types of Nutrition Autotrophs make their own organic compounds from inorganic sources Photoautotrophs harness sunlight for energy and useCO 2 for carbon Chemoautotrophs obtain energy from inorganic chemicals instead of from sunlight Heterotrophs obtain their carbon atoms from organic compounds Photoheterotrophs can obtain energy from sunlight Chemoheterotrophs areso diversethat almost any organic moleculecan serveas food for somespecies Example: E. coli
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The Ecological Importance of Prokaryotes Somebacteria causedisease Pathogenic bacteria causeabout half of human disease , mostly by producing poisons Exotoxins Secreted by cells Produce someof the most toxic poisons known Example: Staphylococcus aureus Harmless bacteria can also develop pathogenic strains
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The Ecological Importance of Prokaryotes Endotoxins
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