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Ethanol fermentation

Fermentation is an anaerobic pathway of producing energy for the cells from sugars. Lactic acid or alcohol are produced as byproducts. Fermentation can be harnessed to produce dairy products such as yogurt using specific strains of bacteria or alcoholic drinks using yeast such as Saccharomyces cerevisiae. The carbon dioxide that is also produced is used in breadmaking.

In alcohol fermentation, yeast converts pyruvate into ethanol (ethyl alcohol), releasing carbon dioxide in the process. There are two steps involved in pyruvate conversion:

  • Release of carbon dioxide from pyruvate, which is converted to the two-carbon compound acetaldehyde
  • Acetaldehyde reduction by NADH to ethanol.

These steps provide a continuous supply of NAD+ for ATP generating glycolysis.

Alcohol fermentation diagram. Thick arrow at top is labelled glycolysis which converts glucose into pyruvate, producing 2 ATP. In this reaction 2 ADP and 2 phosphates join together to create 2 ATP. Below the glycolysis arrow are two arrows forming a circle between 2 NAD plus and 2 NADH and 2 H plus. To the right of the circle is a box indicating that 2 pyruvate from glycolysis are converted to 2 acetaldehyde and 2 carbon dioxide molecules. Below this circle is an arrow from the acetaldehyde to a structure of ethanol labelled alcohol fermentation. Ethanol can be used as a biofuel. The enzyme dehydrogenase converts acetaldehyde into ethanol in order to perform ethanol fermentation.

Figure 1: Alcohol fermentation pathway