Final answer:
Under anaerobic conditions, pyruvate is converted to lactic acid through fermentation, allowing for the continuation of glycolysis and ATP production. In contrast, under aerobic conditions, pyruvate enters the mitochondria and participates in aerobic respiration, converting into acetyl CoA for the citric acid cycle.
Step-by-step explanation:
Under anaerobic conditions, the conversion of pyruvate to acetyl CoA ceases and anaerobic respiration takes place. In anaerobic respiration, pyruvate is converted into lactic acid in a pathway known as fermentation. This process serves two main purposes: it keeps pyruvate levels low to ensure the continuation of glycolysis, and it regenerates NAD+ from NADH, which is crucial for glycolysis to continue producing ATP.
Erythrocytes, which lack mitochondria, and muscle cells during intense exercise, when oxygen delivery is slow, rely on this form of anaerobic ATP production. These cells use fermentation to meet their energy needs temporarily and produce lactic acid as a byproduct. The lactic acid is then transported to the liver via the bloodstream and can be converted back into pyruvate or glucose through the Cori cycle.
In contrast, under aerobic conditions, pyruvate is transported into mitochondria, where it is converted into acetyl CoA. This acetyl CoA is then used in the citric acid cycle as part of aerobic respiration, which ultimately leads to the production of a large number of ATP molecules via oxidative phosphorylation with oxygen as the final electron acceptor.