In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.

Generally, it is always difficult, requiring a large amount of energy to extract electrons from a 2C compound like acetyl CoA, because they are held closer to the nucleus. Therefore C02 production is difficult. However, in compounds with more than 2C atoms it is easier because the attractive forces of the nucleus on the electrons are reduced, and removal of electrons for C02 production will be easy.

Therefore, it is logical to add 2C acetyl CoA to 4C oxaloacetate to form 6C-Citrate, and electrons extracted for C02 molecules liberation as 6C-succinate is converted to 5C-alpha-ketoglutaric and when the latter compound is converted to 4C-succinate. These are many Carbon compounds with easy electrons loss for the liberation of C02 in sequence.

The above steps will be easier than the direct oxidation of 2C acetyl CoA to liberate two molecules of C02.

Explanation: