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Chapter 27

Chapter 27. Prokaryotes and the Origins of Metabolic Diversity. Overview: They’re (Almost) Everywhere!. Most prokaryotes are microscopic, but what they lack in size they make up for in numbers There are more in a handful of fertile soil than the number of people who ever lived

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Chapter 27

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  1. Chapter 27 • Prokaryotes and the Origins of Metabolic Diversity

  2. Overview: They’re (Almost) Everywhere! • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • There are more in a handful of fertile soil than the number of people who ever lived • Prokaryotes thrive almost everywhere, including places too acidic, too salty, too cold, or too hot for most other organisms • They have an astonishing genetic diversity

  3. Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success • Most prokaryotes are unicellular, although some species form colonies • Prokaryotic cells have a variety of shapes • The three most common of which are spheres (cocci), rods (bacilli), and spirals (spirilla).

  4. LE 27-2 1 µm 2 µm 5 µm Spiral (spirilla) Spherical (cocci) Rod-shaped (bacilli)

  5. Cell-Surface Structures • An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment • Using the Gram stain, scientists classify many bacterial species into groups based on cell wall composition, Gram-positive and Gram-negative

  6. Lipopolysaccharide Outer membrane Pepridoglycan layer Cell wall Cell wall Pepridoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria 20 µm Gram-negative Gram-positive

  7. The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein

  8. 200 nm LE 27-4 Capsule

  9. Some prokaryotes have fimbriae and pili, which allow them to stick to their substrate or other individuals in a colony

  10. LE 27-5 Fimbriae 200 nm

  11. Motility • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli

  12. LE 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane

  13. Internal and Genomic Organization • Prokaryotic cells usually lack complex compartmentalization • Some prokaryotes do have specialized membranes that perform metabolic functions

  14. 1 µm 0.2 µm LE 27-7 Respiratory membrane Thylakoid membranes Photosynthetic prokaryote Aerobic prokaryote

  15. The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

  16. Chromosome LE 27-8 1 µm

  17. Classification • Domain: Bacteria • Domain: Archaea • Kingdom: “Monera?” • Shape •cocci (sphere) •bacilli (rod) •helical (spiral)

  18. Structural characteristics • Cell wall~ peptidoglycan (sugars & proteins); • √ Gram +: w/peptidoglycan penicillin action • √ Gram -: little peptidoglycan, lipopolysaccharides; most pathogens; impede drug action • Capsule: adherence; protection • Pili: adherence; conjugation

  19. Motility • 1- Flagella • 2- Helical shape (spirochetes) • 3- Slime • 4-Taxis (movement away or toward a stimulus)

  20. Form & Function • Nucleoid region (genophore: non-eukaryotic chromosome) • Plasmids • Asexual reproduction: binary fission (not mitosis) “Sexual” reproduction (not meiosis): • transformation~ uptake of genes from surrounding environment • conjugation~ direct gene transfer from one prokaryote to another • transduction~ gene transfer by viruses • Endospore: resistant cells for harsh conditions (250 million years!)

  21. Nutrition & Metabolism • Photoautotrophs: photosynthetic; harness light to drive the synthesis of organics (cyanobacteria) • Chemoautotrophs: oxidation of inorganics for energy; get carbon from CO2 • Photoheterotrophs: use light to generate ATP but get carbon in an organic form • Chemoheterotrophs: consume organic molecules for both energy and carbon saprobes- dead organic matter decomposers parasites- absorb nutrients from living hosts • Nitrogen fixation: conversion of atmospheric nitrogen (N2) to ammonium (NH4+) • Oxygen relationships: obligate aerobes; facultative anaerobes; obligate anaerobes

  22. Prokaryotic ecology • Decomposers: unlock organics from corpses and waste products • Symbiosis~ •symbiont/host •mutualism (+, +) •parasitism (+, -) •commensalism (+, 0) • Disease •opportunistic: normal residents of host; cause illness when defenses are weakened •Koch’s postulates: criteria for bacterial disease confirmation •exotoxins: bacterial proteins that can produce disease w/o the prokaryote present (botulism) •endotoxins: components of gram - membranes (Salmonella)

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