Oxidative Decarboxylation
ஆக்சிஜனேற்ற கார்பாக்சில் நீக்கம்
Stop confusing Glycolysis with the Krebs cycle. Pyruvate is not the fuel for the Krebs cycle; Acetyl-CoA is. Oxidative decarboxylation is the mandatory bridge between the cytoplasm and the mitochondrial matrix.
The idea
Pyruvate enters the mitochondrial matrix. The Pyruvate Dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate. This reaction produces Acetyl-CoA, CO2, and NADH + H+. It requires cofactors like Mg2+, NAD+, and Coenzyme A.
Why it matters
It acts as a bridge reaction connecting glycolysis to the Krebs cycle, preparing the pyruvate molecule for complete oxidation.
NEET lens
NEET focuses on the cofactors and the location of the reaction. Remember: this is the 'Link Reaction'. Do not miss the production of NADH; it is a frequent calculation trap in respiration questions.
Clinical significance
Deficiency in the Pyruvate Dehydrogenase complex leads to lactic acidosis. The brain, which relies heavily on aerobic respiration, suffers severe neurological damage when this conversion fails. Energy production halts at the pyruvate stage.
Introduction
Oxidative decarboxylation is the process where an organic acid loses a CO₂ (decarboxylation) while being simultaneously oxidized (losing electrons to NAD⁺ → NADH), connecting glycolysis to the Krebs cycle.
Core concept
Key reactions in respiration involving oxidative decarboxylation: (1) Pyruvate → Acetyl-CoA: pyruvate (3C) → acetyl-CoA (2C) + CO₂ + NADH (by PDC). (2) Isocitrate → α-ketoglutarate: isocitrate (6C) → α-ketoglutarate (5C) + CO₂ + NADH (in Krebs). (3) α-ketoglutarate → succinyl-CoA: (5C) → succinyl-CoA (4C) + CO₂ + NADH (in Krebs). Total CO₂ released from glucose: glycolysis = 0, pyruvate oxidation = 2, Krebs = 4. Total = 6 CO₂.
Go deeper
All three oxidative decarboxylation reactions in respiration are irreversible and use similar multienzyme complexes: PDC and α-ketoglutarate dehydrogenase complex are structurally homologous, using same cofactors (TPP, lipoic acid, CoA, FAD, NAD⁺).
From Class 10
Between glycolysis and the Krebs cycle, pyruvate loses a carbon as CO₂ while being oxidized. This two-step process — decarboxylation and oxidation — is called oxidative decarboxylation.