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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
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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
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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
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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
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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
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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
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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
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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)
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Describe homofermentative lactate fermentation (detail)
- End product is lactic acid
- 2 ATP by substrate-level phosphorylation
- Uses glycolytic pathway
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Describe heterofermentative lactate fermentation (detail)
- Pathway converts glucose to ethanol, lactate, and CO2
- Uses phosphokefolase pathway NOT glycolytic pathway
- Leuconostoc
- Only one ATP / glucose
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Mixed acid fermentation info (general)
- End products are succinate, CO2, H2(g), acetate, lacate, and ethanol
- Succinate from PEP
- All others from pyruvate
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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
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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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