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Fermentation Overview

• Fermentation is a metabolic pathway to regenerate NAD⁺ for glycolysis under anaerobic conditions.

Differences from Cellular Respiration

• Fermentation yields only 2 ATP per glucose, compared to 29 ATP in aerobic respiration.

• No terminal electron acceptor in electron transport chain (ETC) leads to fermentation.

NAD⁺ Regeneration

• NAD⁺ is crucial for glycolysis; without it, ATP production halts.

• Fermentation reduces pyruvate to regenerate NAD⁺ by utilizing NADH from glycolysis.

Types of Fermentation

• Lactic Acid Fermentation:

  • Occurs in muscle cells; pyruvate is reduced to lactate.

  • Lactic acid can return to pyruvate when oxygen becomes available.

• Alcohol Fermentation:

  • In yeast (e.g., Saccharomyces cerevisiae), pyruvate converts to acetaldehyde and then ethanol, regenerating NAD⁺.

  • Produces CO₂, causing bread to rise. Ethanol is excreted as waste.

Role of Anaerobes

• Obligate anaerobes rely solely on fermentation.

• Found in intestines and cow’s rumen, useful for energy production from fermentation by-products.

Facultative Anaerobes

• Organisms can switch between fermentation and aerobic respiration based on oxygen availability.