Final answer:
The three fates of pyruvate in carbohydrate metabolism include entry into the TCA cycle as acetyl-CoA when the cell's energy is low, conversion to lactate by lactate dehydrogenase during oxygen-limited conditions, and conversion to alanine or packaging as lipid when energy is abundant.
Step-by-step explanation:
The three fates of pyruvate in carbohydrate metabolism are a crucial regulatory point for energy production. When a cell has low energy (high ADP; low ATP), pyruvate is converted into acetyl-CoA via the pyruvate dehydrogenase complex and enters the TCA cycle, fully oxidizing to CO₂ and H₂O to yield energy. If the cell has high energy, pyruvate can be transformed into acetyl-CoA and then stored as lipid.
During oxygen-limited conditions, such as intense exercise, pyruvate is converted to lactate by lactate dehydrogenase. Lastly, pyruvate can also be converted to the amino acid alanine through transamination. Phase 1 of carbohydrate metabolism, glycolysis, produces pyruvate which then undergoes different fates based on the cell's energy needs and oxygen availability.