Overview
This lecture covers fermentation, its differences from aerobic and anaerobic respiration, the biological importance of fermentation, and its uses in food and health.
Respiration Overview
- Aerobic respiration uses oxygen as the final electron acceptor and generates 36-38 ATP per glucose.
- Anaerobic respiration uses non-oxygen inorganic substances (e.g., nitrate) as electron acceptors, yielding 5-36 ATP depending on the acceptor.
- Facultative anaerobes like E. coli can switch between aerobic and anaerobic respiration.
Fermentation Process
- Fermentation uses an organic molecule (often pyruvate) as the final electron acceptor.
- Glycolysis breaks down glucose into pyruvate, producing 2 ATP and 2 NADH.
- Fermentation regenerates NAD+ by converting pyruvate into products like lactate, allowing glycolysis to continue.
- No additional ATP is generated from fermentation itself.
Importance and Examples of Fermentation
- Lactic acid fermentation is the primary fermentation type discussed, converting pyruvate to lactate in low-oxygen conditions (e.g., muscle cells).
- Lactic acid bacteria ferment milk into yogurt or cheese by lowering pH and causing curdling.
- Lactic acid producers in the human gut and vaginal microbiome keep pH low, limiting pathogenic bacteria growth.
- Foods like sauerkraut, yogurt, and cheese are preserved by lactic acid fermentation due to low pH.
- Fermentation produces useful end products like solvents, ethanol, beer, wine, butter, pharmaceuticals, and Swiss cheese.
- Unlike respiration, fermentation leaves end products with much of their original energy.
Key Terms & Definitions
- Aerobic Respiration — Energy production using oxygen as the final electron acceptor.
- Anaerobic Respiration — Energy production using substances other than oxygen as the final electron acceptor.
- Facultative Anaerobe — An organism that can switch between aerobic and anaerobic metabolism.
- Fermentation — Anaerobic process that regenerates NAD+ by converting pyruvate into organic end products, enabling glycolysis.
- Lactic Acid Fermentation — Fermentation type converting pyruvate to lactic acid, crucial in muscles, food, and microbiomes.
- NAD+/NADH — Electron carriers; NAD+ is regenerated during fermentation.
Action Items / Next Steps
- Review glycolysis and its role in ATP and NADH production.
- Learn examples of fermentation in food and human health.
- Prepare for questions about the advantages and end products of fermentation vs. respiration.