Fermentation produces a net of 2 ATP molecules per molecule of glucose.
While glycolysis, the first stage of both cellular respiration and fermentation, yields 2 ATP, fermentation itself doesn't directly produce any additional ATP. Instead, its crucial role is to regenerate the NAD+ necessary for glycolysis to continue. Here's a more detailed breakdown:
Glycolysis: The Common Starting Point
- Glycolysis breaks down glucose into two molecules of pyruvate.
- This process yields a net gain of 2 ATP molecules and 2 NADH molecules.
The Role of Fermentation
- Under anaerobic (oxygen-lacking) conditions, the pyruvate doesn't proceed to the Krebs cycle and electron transport chain.
- Instead, fermentation occurs. Its primary function is to regenerate NAD+ from NADH. This is essential because glycolysis needs NAD+ to continue producing ATP.
- Different types of fermentation exist (e.g., lactic acid fermentation, alcoholic fermentation), but none of them directly generate ATP.
Why only 2 ATP?
Because fermentation doesn't involve the Krebs cycle or the electron transport chain (which requires oxygen), the potential energy stored in pyruvate remains largely untapped. These processes, used in aerobic respiration, are far more efficient at extracting energy from glucose, leading to a much higher ATP yield.
In summary, although glycolysis initially produces 2 ATP, fermentation allows glycolysis (and thus ATP production) to continue in the absence of oxygen by regenerating NAD+.
