The link reaction oxidizes and decarboxylates pyruvate in the mitochondrial matrix, forming acetyl-CoA for Krebs cycle entry, supporting usable cellular work and measurable biological activity.
Coverage 2012–2024 · Updated 15 Jul 2026
In the mitochondrial matrix, the link reaction oxidizes and decarboxylates pyruvate and transfers the remaining two-carbon acetyl group to coenzyme A.
One carbon is released as carbon dioxide, hydrogen/electrons reduce NAD, and the 2C acetyl group joins coenzyme A to form acetyl-CoA for entry into the Krebs cycle.
Per pyruvate: one CO₂, one reduced NAD and one acetyl-CoA; no ATP is formed directly. Per glucose, these outputs double because glycolysis produces two pyruvate.
Carbohydrate-derived pyruvate and fatty-acid breakdown can both supply 2C acetyl groups; coenzyme A carries those groups into the Krebs cycle.
The link reaction is not a cycle and does not directly synthesize ATP. It links glycolysis or lipid breakdown to acetyl-group oxidation.
This objective is assessed through structured response, commonly using Label / State / Identify.
Label / State / Identify / Describe / Explain / Outline
Build the answer around this relationship: The link reaction occurs in the mitochondrial matrix.
Representative question
C3. Explain the link reaction that occurs between glycolysis and the Krebs cycle.
In HL respiration, carbon and hydrogen are followed separately. Glycolysis turns glucose into pyruvate, net ATP, and reduced NAD. Without oxygen, pyruvate becomes lactate in humans or ethanol and carbon dioxide in yeast to regenerate NAD. With oxygen, pyruvate enters the link reaction, forming acetyl-CoA, carbon dioxide, and reduced NAD. The Krebs cycle releases more carbon dioxide and reduced coenzymes. Electron transport uses reduced NAD/FAD to pump protons, chemiosmosis through ATP synthase makes ATP, and oxygen accepts electrons and protons to form water. Substrate comparisons depend on ATP yield, oxygen demand, water production, and speed. Regenerated NAD allows glycolysis to continue. Fermentation regenerates NAD for glycolysis and is used in baking and brewing. Electron transfers release energy while coenzymes are reoxidized.
