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ATP Synthesis in Cells

All cells synthesize ATP via glycolysis. In the absence of oxygen, pyruvic acid undergoes fermentation, allowing for the regeneration of NAD+, which is essential for continuous ATP production through glycolysis. The net energy yield from fermentation is two ATP molecules per glucose molecule.

Types of Fermentation

Two main types of fermentation are:

1. Alcohol Fermentation: Occurs in yeast; produces ethanol and carbon dioxide. Pyruvic acid loses one carbon (as CO2) and is reduced to ethanol, regenerating NAD+ from NADH.
2. Lactic Acid Fermentation: Occurs in muscle cells; produces lactic acid. Pyruvic acid is reduced to lactate, also regenerating NAD+ from NADH.

Relationship Between Glycolysis and Fermentation

During glycolysis, NADH, ATP, and pyruvate are produced. In the absence of oxygen, NADH cannot be oxidized via the electron transport chain, leading to a depletion of NAD+. Fermentation is crucial to oxidize NADH, thus maintaining a supply of NAD+ for glycolysis, allowing ATP production to continue under anaerobic conditions.