Pyruvate oxidation, also known as the link reaction, is a crucial step linking glycolysis to the citric acid cycle. It converts pyruvate, produced during glycolysis, into acetyl-CoA, which can then enter the citric acid cycle to further generate energy. This process occurs within the mitochondrial matrix in eukaryotes. The steps involved are as follows:
Steps of Pyruvate Oxidation:
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Decarboxylation: Pyruvate (a 3-carbon molecule) enters the mitochondrial matrix. A carboxyl group (-COO⁻) is removed from pyruvate and released as carbon dioxide (CO₂). This is the first time carbon dioxide is released during cellular respiration.
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Oxidation: The remaining two-carbon fragment (an acetyl group) is oxidized. During this oxidation, electrons are transferred to NAD⁺ (nicotinamide adenine dinucleotide), reducing it to NADH. This is a redox reaction where the acetyl group loses electrons (oxidation) and NAD⁺ gains electrons (reduction). NADH carries these electrons to the electron transport chain for ATP production.
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Acetyl-CoA Formation: The oxidized acetyl group (two-carbon molecule) binds to Coenzyme A (CoA), a large organic molecule. This forms acetyl-CoA (acetyl coenzyme A). Acetyl-CoA is a high-energy molecule due to the unstable thioester bond between the acetyl group and CoA. This energy is used to transfer the acetyl group to oxaloacetate in the first step of the citric acid cycle.
Summary Table:
| Step | Description | Reactants | Products |
|---|---|---|---|
| Decarboxylation | Removal of a carbon atom from pyruvate, releasing carbon dioxide. | Pyruvate | Acetyl group, CO₂ |
| Oxidation | Oxidation of the acetyl group, reducing NAD⁺ to NADH. | Acetyl group, NAD⁺ | Acetyl group, NADH |
| Acetyl-CoA Formation | Binding of the oxidized acetyl group to Coenzyme A to form acetyl-CoA. | Acetyl group, CoA | Acetyl-CoA |
In essence, pyruvate oxidation transforms a 3-carbon pyruvate molecule into a 2-carbon acetyl-CoA molecule, releasing one molecule of CO₂ and one molecule of NADH in the process. This process is a critical preparatory step for the citric acid cycle and further ATP production.
