Wk 7 Lec 1

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 The oldest life-forms Remain the most numerous and widespread organisms today Survive in environments too extreme for eukaryotes Despite being small, prokaryotes have an 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 are the two main branches of prokaryotic evolution Domains Bacteria and Archaea Probably evolved from a common ancestor Differ in nucleotide sequences and other molecular features Peptidoglycan present in bacteria but not archaea Archaea are more like eukaryotes than like bacteria
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Prokaryote Structure Prokaryotes come in 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 be covered by a capsule that aids in protection, adhesion Distinguished as gram positive or 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 Have a propeller-like structure very different from eukaryotic flagella Internal organization Simpler than eukaryotic cells in both structure and organization of genome About one-thousandth as much DNA as eukaryote Some have specialized membranes that perform metabolic functions
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Prokaryote Reproduction In favorable environments 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 use CO 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 are so diverse that almost any organic molecule can serve as food for some species Example: E. coli
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The Ecological Importance of Prokaryotes Some bacteria cause disease Pathogenic bacteria cause about half of human disease , mostly by producing poisons Exotoxins Secreted by cells Produce some of the most toxic poisons known Example: Staphylococcus aureus Harmless bacteria can also develop pathogenic strains
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This note was uploaded on 09/23/2011 for the course BIO 141 taught by Professor Brown during the Fall '08 term at Drexel.

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

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