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MIBO 4300 Study guide 3

MIBO 4300 Study guide 3 - TEST 3 1 Two organisms grow in...

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TEST 3 1. Two organisms grow in the presence of air. One is an aerotolerant anaerobe and the other is a facultative aerobe. How might you tell which is which? The facultative aerobe will produce a higher yield of energy (ATP) than the aerotolerant anaerobe. 2. What is the rationale for magnetism in the magnetotactic bacteria? There is a row of iron-containing crystals aligned with the long axis of the cell, giving them the equivalent of an internal magnetic compass needle as consequence of metabolic byproduct. The magnetotactic bacteria we know about require low but very precise levels of oxygen to survive, and must live in sediments where the oxygen concentration is just right for their needs. Over much of the globe, the Earth’s magnetic field actually points down towards the centre of the planet, so by following these lines of magnetic flux, they are able to ensure that they bury themselves in the sediment, which is exactly where they want to be. Thus the majority of magnetotactic in the Northern Hemisphere are north seeking, and those in the Southern Hemisphere are south seeking. 3. Describe the magnetosome, what is it composed of and where it is found in the cell. A membranous prokaryotic organelle in magnetotatic bacteria that is composed of 15-20 magnetic crystals that align towards the magnetic field. Magnetosomes are invaginations of the inner membrane. 4. Describe the reactive intermediates formed during the reduction of O 2 . In the cell, what initiates the formation of these compounds? Reduction of O2 produces very reactive intermediates. Superoxide (O2)- anion formed by one electron reduction of O2 Hydrogen peroxide (H2O2)- one electron reduction from superoxide Hydroxyl Radical (OH)- one electron reduction of H2O2, extremely reactive and probable cause of major O2 toxicity Initiates by metal chelates 5. What are the mechanisms of O 2 toxicity? How do superoxide dismutase, catalase, and peroxidase protect against O 2 toxicity? For protection, they degrade the substrates for formation of OH radical and REDUCE the amounts of O2 in the cell. SOD- reduces O2- H2O2 + O2, Mn-SOD, Fe-SOD, Cu/Zn-SOD Catalase- degrades H2O2 to H2O and ½ O2 Peroxidase- degrades H2O2 with needed reductant to 2H2O
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6. Describe other methods bacteria protect themselves against O 2 toxicity. Why might anaerobes be especially O 2 sensitive? Carotenoids- long, conjugated alkenes that react w/ singlet O2 (photosynthetic bacteria and soil bacteria) Intracellular thiols- cystiene, glutathione (glycine-cysteine-glutamine), H2S, and coenzyme o Thiols react w/ O2 and lower [intracellular] o Thiols reduce disulfides (product of cystiene oxidation), formalydehyde Respiratory protection- aerobes that consume O2 via respiration faster than O2 can diffuse in the cell, thus, [O2] lower in cytoplasm, Anaerobes are sensitive to O2 b/c they: Strong reductants are necessary in their metabolism, and aerobes
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MIBO 4300 Study guide 3 - TEST 3 1 Two organisms grow in...

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