When oxygen is available, pyruvate is converted to which molecule to enter the Krebs cycle?

When oxygen is available, pyruvate is converted to acetyl CoA before it enters the Krebs cycle. This conversion occurs in the mitochondria, where the enzyme pyruvate dehydrogenase facilitates the decarboxylation of pyruvate, resulting in the release of carbon dioxide and the generation of acetyl CoA. Acetyl CoA acts as a key entry point into the Krebs cycle, combining with oxaloacetate to form citric acid, which undergoes further reactions in the cycle.

This process is crucial because acetyl CoA is the primary substrate that feeds into the Krebs cycle, allowing for the continuation of aerobic respiration and the production of energy in the form of ATP. The conversion of pyruvate to acetyl CoA is an important regulatory step that links glycolysis (which occurs in the cytoplasm) to the Krebs cycle (which occurs in the mitochondria), highlighting the intricate coordination between aerobic metabolism and energy production.

In situations where oxygen is not present, pyruvate would instead be converted into lactic acid in animals or ethanol in yeast, but those pathways are not the focus when oxygen is available and the Krebs cycle is active.