Fermentation Flashcards
Define fermentation
- anaerobic catabolism of organic compound which serves as electron donor and acceptor
Anaerobic prokaryotes re-oxidize ____ by respiration or _______.
- NADH by fermentation
What does adding mineral oil do?
- decreases O2 and inhibits growth of aerobic organisms
What happens in the absence of an external electron acceptor?
- organic compounds can be catabolized ONLY by fermentation
only certain compounds are fermentable, what is required for most fermentations?
- energy-rich organic intermediate formed that can yield ATP by substrate-level phosphorylation
- redox balance
What is a means of disposing excess electrons?
- production of H2, associated with presence of iron-sulfur protein ferredoxin
What is ferridoxin?
- very low potential electron carrier
What is the transfer of electrons from ferredoxin to H2 catalyzed by?
- hydrogenase
How do you protect from too much acidity?
- remove electron acceptors
What is a key product of many fermentative processes?
- pyruvate
What has fermentative metabolism?
- acids and ethanol
What puts holes in swiss cheese?
- propionibacterium
What are carbohydrate fermentations?
- lactic
- ethanol
- butyric
- mixed acid
- propionic
- homeoacetic
What does it mean that there is considerable diversity in fermentation?
- product of one organisms fermentation is fermented by a second organism
- some employ ion gradients as basis for energetics across membrane
What happens when inadequate energy is released?
Coupled to ATP synthesis directly by substrate-level phosphorylation
What compounds can still support growth of the organism with inadequate energy?
- succinate and oxalate
What ferments succinate?
- propionigenium modestrum
What does chemiosmotic ATP formation result from?
- Na+ pump (decarboxylation of organic acids)
-ex. decarboxylation of succinate coupled to export of sodium across cytoplasmic membrane
What happens during oxalate decarboxylation?
- decarboxylated to formate = build-up of proton motive force from exportation of formate
Explain the anaerobic food chain
- fermentation of amino acids, carbs, purines and pyrimidines to organic acids and alcohols followed by conversion to CO2, H2, and acetate
- methanogens convert compounds to CH4 and CO2
What is the fermentation pathway of Clostridium propionicum?
- lactate oxidized to pyruvate
- pyruvate oxidized to acetyl-CoA and CO2
- acetyl-CoA converted to acetate and ATP by acetyl-P
- lactate acquires CoA from propionyl-CoA
- lactyl-CoA dehydrated to acrylyl-CoA –> reduced to propionyl-CoA
What is the overall equation for fermentation of clostridium propionicum?
- 2 lactate –> 2 propionate + acetate + CO2 + H2O (3ATP)
What is the simplified pathway of fermentation of clostridium propionicum?
- Lactate –> pyruvate = 3 ATP and acetate
- feeds back on self, picks up CoA to generate propionate and CoA transfer
How many moles of ATP per molecule of acetate are generated when bacteria are growing on glucose using the EMP pathway?
- 2
