Where in the cell does pyruvate conversion to acetyl‑CoA occur under aerobic conditions, enabling entry into the citric acid cycle?

• A. In the extracellular space where pyruvate is oxidized by plasma enzymes before re-entering muscle cells for the TCA cycle.
• B. Within the sarcoplasmic reticulum where acetyl‑CoA is stored until needed for anaerobic glycolysis.
• C. In the rough endoplasmic reticulum by ribosomal enzymes that synthesize acetyl‑CoA directly from pyruvate.
• D. Inside the mitochondria (mitochondrial matrix), via the pyruvate dehydrogenase complex.

Answer: (D)