In this video, we're going to briefly introduce lactic acid fermentation. Lactic acid fermentation is when pyruvate is reduced by NADH to form lactic acid or lactate along with NAD+ that's ultimately going to help drive glycolysis. Notice in our image below that we're showing you lactic acid fermentation. Notice that when there's absolutely no oxygen, the normal processes that we've talked about for aerobic cellular respiration such as pyruvate oxidation, the Krebs cycle, and the electron transport chain in chemiosmosis cannot occur. However, glycolysis is going to be able to occur and the reason for that is because lactic acid fermentation, represented by this red arrow right here, is going to ultimately generate lactic acid or lactate, and the pyruvate here is going to get reduced instead of being oxidized like it was normally with step 2 of aerobic cellular respiration. So the pyruvate is going to get reduced because it's going to be gaining electrons and ultimately it's gonna be converted to lactic acid. And through this lactic acid fermentation here, the big part is that it regenerates the NAD+ here, the empty electron taxicab. And this empty electron taxicab, the NAD+, is needed in order for glycolysis to continue forward. Ultimately, lactic acid fermentation is allowing for glycolysis to produce 2 ATP molecules. And a little bit of ATP is certainly better than no ATP molecules at all. Lactic acid fermentation will allow for a small amount of ATP to be made via glycolysis.
Lactic acid fermentation actually occurs in human muscle cells, but it can also occur in bacteria as well. When it does occur in bacteria, this is what gives yogurt its sour taste. Notice down below on the right-hand side of the image, we're showing you a human muscle to remind you that lactic acid fermentation will occur in our muscle cells during strenuous exercise when our muscles are low on oxygen. Lactic acid fermentation allows our muscles to still produce a little bit of energy via ATP. However, the small amount of ATP produced via glycolysis is not going to be enough to sustain our muscle cells for a long time. Then we'll have to stop performing the exercise so that we can get more oxygen and allow our normal aerobic cellular respiration to take place. Lactic acid fermentation can also occur in bacteria found in yogurt, which gives yogurt, once again, its sour taste. This concludes our brief introduction to lactic acid fermentation, and in our next video, we'll talk about alcohol fermentation. So I'll see you all there.