When oxygen is available, the pyruvate from glycolysis is actively transported into the mitochondrial matrix, where the link reaction takes place. It links glycolysis to the Krebs cycle.In the link reaction, each pyruvate (3C) is:
• decarboxylated: a carbon atom is removed as carbon dioxide;
• dehydrogenated: hydrogen is removed and accepted by NAD, forming reduced NAD.This leaves a 2-carbon acetyl group (acetate), which combines with coenzyme A to form acetyl coenzyme A (acetyl CoA). Coenzyme A carries the acetyl group into the Krebs cycle.
pyruvate + NAD + CoA → acetyl CoA + CO2 + reduced NAD Because one glucose gives two pyruvate, the link reaction happens twice per glucose. The products per glucose are:
• 2 acetyl coenzyme A
• 2 carbon dioxide
• 2 reduced NAD
• no ATPThe carbon dioxide diffuses out of the mitochondrion and the cell as a waste product. The reduced NAD carries hydrogen to the electron transport chain, where it is used to make ATP by oxidative phosphorylation.The link reaction needs oxygen indirectly: it only continues if NAD is regenerated by the electron transport chain, which requires oxygen as the final electron acceptor. The steps are catalysed by a large enzyme complex in the matrix.
• decarboxylated: a carbon atom is removed as carbon dioxide;
• dehydrogenated: hydrogen is removed and accepted by NAD, forming reduced NAD.This leaves a 2-carbon acetyl group (acetate), which combines with coenzyme A to form acetyl coenzyme A (acetyl CoA). Coenzyme A carries the acetyl group into the Krebs cycle.
• 2 acetyl coenzyme A
• 2 carbon dioxide
• 2 reduced NAD
• no ATPThe carbon dioxide diffuses out of the mitochondrion and the cell as a waste product. The reduced NAD carries hydrogen to the electron transport chain, where it is used to make ATP by oxidative phosphorylation.The link reaction needs oxygen indirectly: it only continues if NAD is regenerated by the electron transport chain, which requires oxygen as the final electron acceptor. The steps are catalysed by a large enzyme complex in the matrix.