The net ATP yield when one molecule of pyruvate is completely oxidized to CO2 & H2O is:
**Core Concept**
The question tests the understanding of cellular respiration, specifically the citric acid cycle and oxidative phosphorylation. The complete oxidation of pyruvate to CO2 and H2O involves the conversion of pyruvate to acetyl-CoA, which then enters the citric acid cycle, followed by the electron transport chain.
**Why the Correct Answer is Right**
The correct answer is based on the fact that one molecule of pyruvate yields one molecule of acetyl-CoA, which produces 3 NADH, 1 FADH2, and 1 GTP (via the citric acid cycle). The electron transport chain then generates approximately 2.5 ATP per NADH and 1.5 ATP per FADH2. Calculating the total ATP yield from these coefficients gives a net yield of 32.5 - 33 ATP per pyruvate molecule, but considering the transport of NADH from the cytosol into the mitochondria, the yield is around 32-33, but most commonly rounded to a specific number for simplicity.
**Why Each Wrong Option is Incorrect**
**Option A:** This option underestimates the ATP yield from the complete oxidation of pyruvate.
**Option B:** This option overestimates the yield, not accounting for the inefficiencies in the electron transport chain.
**Option D:** This option severely underestimates the ATP yield, not considering the major contribution of the electron transport chain.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the complete oxidation of one glucose molecule (via glycolysis, pyruvate oxidation, and the citric acid cycle) yields approximately 36-38 ATP, with the majority coming from the oxidation of pyruvate in the mitochondria.
**Correct Answer:** Correct Answer: C. 32-33 ATP