The Complete Oxidation of Pyruvic Acid

Pyruvic acid is the end product of glycolysis, which takes place in the cytoplasm of the cell. The complete oxidation of pyruvic acid takes place in the mitochondria, and it involves three steps:

1. Pyruvic acid decarboxylation: In this step, pyruvic acid loses a carbon atom in the form of CO2, and the remaining two-carbon acetyl group is attached to coenzyme A (CoA) to form acetyl-CoA.

2. Citric acid cycle: In this step, acetyl-CoA enters the citric acid cycle, which is also known as the Krebs cycle. During the citric acid cycle, acetyl-CoA is oxidized into CO2, and several molecules of NADH and FADH2 are produced.

3. Electron transport chain: In this step, the NADH and FADH2 produced during the citric acid cycle donate their electrons to the electron transport chain, which generates ATP through oxidative phosphorylation.

The Production of NADH and FADH2

During the complete oxidation of one molecule of pyruvic acid, the following molecules of NADH and FADH2 are produced:

- Pyruvic acid decarboxylation: One molecule of NADH is produced during pyruvic acid decarboxylation.

- Citric acid cycle: Two molecules of NADH and one molecule of FADH2 are produced during the citric acid cycle.

Therefore, the total number of molecules of NADH and FADH2 produced during the complete oxidation of one molecule of pyruvic acid is:

- NADH: 1 (from pyruvic acid decarboxylation) + 2 (from the citric acid cycle) = 3

- FADH2: 1 (from the citric acid cycle) = 1

Therefore, the correct answer is option D, which states that four molecules of NADH and one molecule of FADH2 are produced during the complete oxidation of one molecule of pyruvic acid in mitochondria.

One NADH + H⁺ produced in link reaction and 3NADH + H⁺ and one FADH + H⁺ produced in Krebs cycle.