21 Which of the following best describes the cellular location where pyruvate dehydrogenase is most likely active (a) A The mitochondrial matrix B The cytosol C The nucleus D The lysosomes

The correct answer is (a) The mitochondrial matrix.<br /><br />Pyruvate dehydrogenase is an enzyme complex that plays a crucial role in cellular respiration, specifically in the conversion of pyruvate to acetyl-CoA. This process occurs in the mitochondrial matrix, which is the innermost compartment of the mitochondria. The mitochondrial matrix is the site where the citric acid cycle (also known as the Krebs cycle or TCA cycle) takes place, and acetyl-CoA is a key substrate for this cycle. Therefore, pyruvate dehydrogenase is most likely active in the mitochondrial matrix.