Final answer:
Two out of the six CO₂ molecules produced from the complete oxidation of one glucose molecule are from the oxidation of pyruvate to acetyl CoA, which represents one-third or 33.33% of the CO₂ produced during respiration when glucose is the sole energy source.
Step-by-step explanation:
Understanding the Oxidation of Pyruvate to Acetyl CoA
In cellular respiration, glucose undergoes a series of metabolic pathways to be converted into carbon dioxide (CO₂) and water (H₂O). The question asks what fraction of the CO₂ exhaled by animals is produced during the conversion of pyruvate to acetyl coenzyme A (acetyl CoA) when glucose is the only energy source. During this reaction, one CO₂ molecule is produced for each pyruvate molecule oxidized. Since one glucose molecule yields two pyruvates, this means two CO₂ molecules are released at this stage for every glucose molecule metabolized.
The oxidation of pyruvate to acetyl CoA is a step in the broader context of the citric acid cycle (also known as the Krebs cycle or TCA cycle), which produces four additional CO₂ molecules from the acetyl CoA derived from one glucose molecule. Therefore, two out of the total six CO₂ molecules produced from one glucose molecule are from the oxidation of pyruvate to acetyl CoA, which is one-third or 33.33%.
Importantly, this conversion is also where the chemical potential energy of glucose begins to be transferred to electron carriers like NADH, which will eventually contribute to the production of ATP through oxidative phosphorylation. For every complete oxidation of one glucose molecule, a total of six CO₂ molecules are produced, with two being released during the conversion of pyruvate to acetyl CoA.