Fermentation

Overview of Fermentation

  • Fermentation is an anaerobic process that takes place when oxygen (O$_2$) is not available for cellular respiration.

  • It allows cells to convert glucose into usable energy through different pathways.

Glycolysis

  • The process begins with glycolysis, which breaks down glucose (a 6-carbon sugar) into pyruvate, yielding:

    • 2 molecules of ATP

    • 2 molecules of NADH

  • Full glycolysis equation:
    \text{Glucose} \rightarrow 2\text{Pyruvate} + 2\text{ATP} + 2\text{NADH}

Pyruvate Metabolism

  • After glycolysis, the fate of pyruvate varies by organism and cell type, leading to two major fermentation pathways:

1. Lactic Acid Fermentation

  • Process: Pyruvate (3 carbons) is converted into lactate (3 carbons) without the use of oxygen.

  • This reaction also regenerates NAD$^+$ from NADH, which is used in glycolysis to keep the cycle going:

    • Reaction:
      \text{Pyruvate} \rightarrow \text{Lactate} + NAD^+ + H^+

  • Characteristics:

    • Lactic acid fermentation occurs in red blood cells.

    • Lactate can be converted back to pyruvate when oxygen becomes available again, allowing for cellular respiration to resume.

2. Alcohol Fermentation

  • Process: Pyruvate (3 carbons) is converted into ethanol (2 carbons) and carbon dioxide (CO$_2$) in the absence of oxygen.

  • This pathway also regenerates NAD$^+$ from NADH to continue glycolysis:

    • Reaction:
      \text{Pyruvate} \rightarrow \text{Ethanol} + \text{CO}_2 + NAD^+ + H^+

  • Applications:

    • This type of fermentation is utilized in the production of alcoholic beverages and is also involved in the making of bread.

    • Yeast is primarily responsible for alcohol fermentation in bread-making.