Part 2: Chemoorganotrophic fermentation Flashcards
Why do most anaerobes lack a full array of enzymes?
Anoxic conditions prevent a high energy yield, meaning that anaerobes must use energy sparingly - therefore most lack a full complement of enzymes.
Which group of organisms lack a respiratory chain?
Fermentors.
List 5 economical uses for fermenting bacteria (with examples).
1) Lactic acid fermentation (yoghurt, salami, sauerkraut)
2) Alcoholic fermentation (beer, wine, cider)
3) Propionic acid fermentation - cheese
4) Citric acid fermentation - “lemon juice”
5) Acetone formation - industrial solvent
Give an example of a food-spoiling fermenter and its effects.
Clostridium botulinum - fermentation product is a nerve toxin.
What acts as the electron donor and electron acceptors in fermentation?
The fermentation acts as both donor and acceptor - some C atoms are oxidised, some reduced.
Compare the ATP yield of lactic acid fermentation and aerobic respiration.
Lactic acid fermentation is very inefficient - only 2 ATP per glucose molecule. Respiration yields roughly 25 ATP.
How much more efficient is propionic acid fermentation than lactic acid fermentation?
2.7 ATP per glucose for propionic compared to 2 for lactic.
Why is conversion of pyruvate to formate a problem in fermentation?
An excess electron is produced which cannot be removed by formation of H2, since H2 has a lower redox potential than NADH.
How do fermenters overcome the problem of additional electrons released during fermentation?
Fermenters react with methanogen spp. who are able to take up the additional H2 and who then return some energy to the fermenter.