Link Reaction
- The end product of glycolysis is pyruvate
- Pyruvate contains a substantial amount of chemical energy that can be further utilised in respiration to produce more ATP
- The enzymes and coenzymes that are required for the link reaction are found in the mitochondrial matrix
- When oxygen is available pyruvate will enter the mitochondrial matrix and aerobic respiration will continue
- Pyruvate moves across the double membrane of the mitochondria via active transport
- It requires a transport protein and a small amount of ATP
- Once in the mitochondrial matrix pyruvate takes part in the link reaction
Pyruvate enters the mitochondrial matrix from the cytosol (cytoplasm) by active transport
- The link reaction takes place in the matrix of the mitochondria
- It is referred to as the link reaction because it links glycolysis to the Krebs cycle
- The steps are:
- Pyruvate is oxidised (hydrogen is removed) by enzymes to produce acetate, CH3CO(O) (also known as acetic acid)
- Pyruvate is also decarboxylated (carbon is removed) in the form of carbon dioxide
- Reduction of NAD to NADH or reduce NAD by collecting hydrogen from pyruvate
- Acetate combines with coenzyme A to form acetyl coenzyme A (acetyl CoA)
- No ATP is produced during the link reaction
- It produces:
- Acetyl coA
- Carbon dioxide (CO2)
- Reduced NAD (NADH)
pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD
The link reaction occurs in the mitochondrial matrix. It dehydrogenates and decarboxylates the three-carbon pyruvate to produce the two-carbon acetyl CoA that can enter the Krebs Cycle
- Every molecule of glucose produces two pyruvate molecules
- The link reaction and the Krebs cycle will therefore occur twice for every molecule of glucose
- Thus, each molecule of glucose will produce:
- Two molecules of acetyl CoA
- Two molecules of CO2
- Two molecules of reduced NAD