Final answer:
If oxygen is available, pyruvic acid can continue through aerobic respiration pathways, leading to the production of acetyl CoA and entry into the citric acid cycle. In the absence of oxygen, pyruvate is converted to lactic acid in anaerobic respiration or fermentation.
Step-by-step explanation:
If oxygen is available, pyruvic acid can continue through aerobic respiration pathways. In eukaryotic cells, pyruvate produced at the end of glycolysis is transported into the mitochondria, where it undergoes several transformations. The most significant of these is its conversion into acetyl CoA, a compound that plays a central role in metabolism. Acetyl CoA then enters the citric acid cycle (also known as the Krebs cycle or TCA cycle), where it contributes to the complete oxidation of glucose to carbon dioxide and water while generating high energy molecules like ATP, NADH, and FADH2.
Conversely, in the absence of oxygen, cells shift to anaerobic respiration or fermentation. In this process, pyruvic acid is converted into lactic acid. This conversion is crucial as it helps regenerate NAD+ needed for glycolysis to continue, allowing cells to glean some energy in the form of ATP even when oxygen is scarce. However, this pathway is less efficient and can only sustain the energy needs of cells for short durations, such as during intense muscle activity.