Pyruvate (pyruvic acid)

By Levi Clancy for Student Reader on
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Pyruvic acid (pyruvate) can undergo any of three fates following glycolysis.

In anaerobic conditions, alcoholic fermentation ensues. In aerobic conditions, either lactic acid fermentation or cellular respiration occurs.

Alcoholic fermentation (anaerobic conditions)

Pyruvic acid is decarboxylated and reduced by NADH to form a molecule of carbon dioxide and one of ethanol via alcoholic fermentation. This occurs in yeast. The process is energetically wasteful because so much of the free energy of glucose (some 95%) remains in the alcohol (a good fuel!).

C3H4O3 + NADH + H+ → CO2 + C2H5OH + NAD+

Lactic acid fermentation (aerobic conditions)

Pyruvic acid is reduced by NADH forming a molecule of lactic acid via lactic acid fermentation. This occurs in muscle cells. This process is energetically wasteful since much free energy remains in the lactic acid molecule. Lactate produced in overworked muscles is transported out into the blood, which can cause a debilitating pH drop.

C3H4O3 + NADH + H+ → C3H6O3 + NAD+

Cellular respiration (aerobic conditions)

Pyruvic acid is oxidized completely to form carbon dioxide and water via cellular respiration. This occurs in mitochondria. Approximately 40% of the energy in the original glucose molecule is trapped in molecules of ATP.