Pyruvate is actively transported from the cytoplasm, through the outer and inner membranes of a mitochondrion and into the mitochondrial matrix. Here it is decarboxylated, dehydrogenated and combined with coenzyme A (CoA) to give acetyl coenzyme A. This is known as the link reaction and is an important part of respiration

pyruvate + CoA + NAD -> acetyl CoA + CO2 +NADH2