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2013-04-29 17:09:46

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  1. Determine oxygen toxicity in strict anaerobes, aerobes, and aerotolerants
    • Strict anaerobes: killed by toxic forms of oxygen
    • Superoxide radicals (O2-*) - forms because e- transferred to oxygen one at a time
    • Hydrogen peroxide (H2O2) - form when superoxide radicals are reduced
    • Hydroxyl radicals (OH-*) - forms when H2O2 in presence of transition metals
    • Aerobes and aerotolerants posses enzymes that remove these forms of oxygen.
    • Superoxide dismutases: 2 O2-* +2H -> H2O2 + O2
    • Found in aerobes and aerotolerants
    • Catalases: 2 H2O2 -> 2H2O + O2
    • Found in aerobes
  2. Why is fermentation a less energy efficient process than aerobic or anaerobic processes?
    • Most reactions take place in cytoplasm
    • ATP is made by substrate-level phosphorylation
    • No ETC = no proton gradient = very small amount of ATP production
  3. What is fermentation? Who can do it?
    • A way to regen NAD+ and other electron carriers under anaerobic conditions
    • Different types of carbohydrates yield different products
    • prokaryotes, yeast, muscle cells, and RBCs can ferment
    • Products can be used by other anaerobes in "anaerobic food chain"
    • Important in recycling of organic C
  4. Describe an electron sink
    • In aerobic organisms e- are transported to oxygen or nitrate during respiration
    • In fermentation there are no exogenous e- acceptors, "electron sinks" are the electron acceptors made by fermentors
    • Reduced products (alcohols, acids, solvents) are excreted from cell
  5. Describe proprionate fermentation via the acrylate pathway
    • 3 lactate oxidized to 2 propionate, 1 acetate, 1 CO2, and 1 ATP
    • Fermentation pathway of genus Clostridium
    • Gram positive, endospore forming anaerobes
    • Live in anaerobic soil
    • Can't use SO42- as final e- acceptor, therefor cannot perform anaerobic respiration
  6. Describe propionate fermentation via the succinate-propionate pathway
    • Yields more ATP/mol propionate than acrylate pathway
    • Pathway in genus propionbacterium (acne)
    • Gram positive, non-endospore forming anaerobes
    • Live in rumen of herbivores, human skin, dairy products
  7. Describe acetate formation
    • Acetogenesis: When CO2 is used as an electron sink and is reduced to ACETATE (not farther) via acetyl-CoA pathway
    • oxidation of pyruvate -> acetate
  8. Describe lactate fermentation (general)
    • Lactobacilllus, Streptococcus, Leuconostoc, Bifidobacterium
    • Aerotolerants, ferment glucose -> lactate
    • Found on skins of animals, GI tract, mouth
    • Medically / commercially important: food, normal microbiota
    • Two types: homofermentative (uses glycolysis) and heterofermentative (uses PPP)
  9. Describe homofermentative lactate fermentation (detail)
    • End product is lactic acid
    • 2 ATP by substrate-level phosphorylation
    • Uses glycolytic pathway
  10. Describe heterofermentative lactate fermentation (detail)
    • Pathway converts glucose to ethanol, lactate, and CO2
    • Uses phosphokefolase pathway NOT glycolytic pathway
    • Leuconostoc
    • Only one ATP / glucose
  11. Mixed acid fermentation info (general)
    • End products are succinate, CO2, H2(g), acetate, lacate, and ethanol
    • Succinate from PEP
    • All others from pyruvate
  12. Describe butanediol fermentation
    • Characteristic of pathway in production of acetioin and 2,3 butanediol
    • Pyruvate produced via glycolysis
    • 3 fates of pyruvate...
    • 1. reduction to lactate
    • 2. split -> formate and acetyl-Coa
    • 3. Converted to 2,3 butanediol
  13. Describe butyrate fermentation
    • Carried out by butyric acid clostridia
    • Some can...
    • 1. ferment sugars -> butyric acid
    • 2. break down proteins (putrefication) -> H2S, NH3
    • End products: H2, CO2, and butyric acid
    • Produces 3 ATP / glucose

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