Under aerobic conditions, most cells employ aerobic respiration to generate ATP (adenosine triphosphate). ATP provides the energy needed to fuel other cellular activities. However, when oxygen levels are insufficient for aerobic cellular respiration, some cells employ lactic acid fermentation to produce ATP. The amount of net ATP is greatly reduced in lactic acid fermentation compared to aerobic respiration.
Lactic acid fermentation yields only two molecules of ATP per molecule of glucose, while aerobic respiration produces 36 molecules of ATP, most of which comes from the electron transport chain.
Lactic acid fermentation derives its name from the lactic acid (or lactate) produced by the process. The lactic acid is a waste product of the process, which must be removed by the organism. The accumulation of lactic acid in muscle cells can be felt as a aching sensation during exercise. It also produces the sour taste of yogurt and spoiled milk.
The chemical formula of lactic acid is C3H6O3.
In lactic acid fermentation, glycolysis (which does not require oxygen) splits glucose into two pyruvate molecules. The lactic acid fermentation pathway then converts the pyruvate into lactate. The NAD+ consumed in glycolysis is replenished by lactic acid fermentation.
Some bacteria and fungi undergo lactic acid fermentation as do animal muscle cells.
