Which two routes can pyruvic acid take after glycolysis?

After glycolysis, pyruvic acid can undergo different pathways depending on the availability of oxygen. If oxygen is present, pyruvic acid is transported into the mitochondria where it undergoes aerobic respiration. This involves conversion to acetyl-CoA, which then enters the Krebs cycle, producing energy in the form of ATP and electron carriers (NADH and FADH2) that feed into the electron transport chain.

Conversely, if oxygen is not available (anaerobic conditions), pyruvic acid does not enter the Krebs cycle. Instead, it is converted into lactate in animals (through lactic acid fermentation) or ethanol and carbon dioxide in yeast (alcoholic fermentation). Both of these processes allow for the regeneration of NAD+, which is necessary for glycolysis to continue producing ATP.

Thus, the two routes that pyruvic acid can take—depending on oxygen availability—are through aerobic respiration and anaerobic fermentation. This highlights the importance of oxygen in determining the metabolic fate of pyruvic acid following glycolysis.