Chapter 1, Section 6: Alcoholic Fermentation

Alcoholic Fermentation is another way cells can produce energy without oxygen. It’s used by organisms like yeast and some bacteria. This process is important not only in biology but also in brewing and baking!

What is Alcoholic Fermentation?

Alcoholic fermentation is a type of anaerobic respiration (energy production without oxygen) where cells convert pyruvate into alcohol (ethanol) and carbon dioxide (CO₂). This process also regenerates NAD⁺, allowing glycolysis to keep running and produce a small amount of ATP.

How Alcoholic Fermentation Works:

1. Glycolysis: Just like in lactic acid fermentation, glycolysis breaks down glucose into two pyruvate molecules, producing 2 ATP and 2 NADH.

2. Conversion to Alcohol: When oxygen isn’t available, pyruvate can’t enter the mitochondria for further breakdown. Instead, it’s converted into ethanol (alcohol) and CO₂ by enzymes in the cytoplasm. During this process, NADH donates electrons to pyruvate, turning it back into NAD⁺.

• Pyruvate → Ethanol + CO₂ + NAD⁺

3. Regenerating NAD⁺: This step is essential. By turning NADH back into NAD⁺, the cell can continue glycolysis, allowing it to keep making a small amount of ATP without oxygen.

Where Does It Occur?

• Yeast: Yeast cells use alcoholic fermentation to produce energy without oxygen. This is why yeast is used in brewing (to produce alcoholic drinks like beer and wine) and in baking (the CO₂ makes bread rise).

• Some bacteria: Certain bacteria can also use alcoholic fermentation, but yeast is by far the most well-known organism for this process.

Why Alcoholic Fermentation Matters:

• Energy Production: Though it’s not very efficient (only 2 ATP per glucose), alcoholic fermentation allows cells to produce energy when oxygen is unavailable.

• Food and Beverage Production: Humans have used alcoholic fermentation for centuries to produce bread, beer, and wine. The ethanol gives alcoholic beverages their effect, while the CO₂ helps leaven bread.

Summary: Alcoholic fermentation is an anaerobic process where cells convert pyruvate into ethanol and CO₂, regenerating NAD⁺ so glycolysis can continue to produce ATP in low-oxygen conditions.