From two molecules of pyruvic acid derived from one glucose, the oxidative decarboxylation step in mitochondria produces how many NADH molecules?

The correct option is 2.

Explanation

Oxidative decarboxylation, commonly known as the "link reaction," connects glycolysis to the Krebs cycle (Citric Acid Cycle). This process takes place in the mitochondrial matrix, where pyruvic acid is converted into Acetyl-CoA under the influence of the pyruvate dehydrogenase enzyme complex.

Detailed Analysis

• Input from Glycolysis: The breakdown of one molecule of glucose during glycolysis yields two molecules of pyruvic acid (pyruvate).
• Reaction Mechanism: During the link reaction, pyruvate undergoes decarboxylation (removal of CO₂) and oxidation (removal of hydrogen). The hydrogen is transferred to NAD⁺ to form NADH.
• Stoichiometry per Pyruvate:
  Pyruvate + NAD⁺ + CoA → Acetyl-CoA + NADH + H⁺ + CO₂
  Thus, 1 NADH is produced for every single molecule of pyruvic acid.
• Total Yield: Since the question specifies "two molecules of pyruvic acid" (derived from one glucose), the reaction occurs twice.
  Total NADH = 1 NADH × 2 = 2 NADH molecules.

Key Takeaway: The oxidative decarboxylation step for one glucose molecule (involving two pyruvates) produces a net total of 2 NADH, 2 Acetyl-CoA, and 2 CO₂ molecules.