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.

Since acetyl-CoA is a 2-carbon compound, it is easier to remove electrons and produce CO2 from 2-carbon compounds than 3 or more carbon compounds. Although it is possible to oxidize the Acetyl group which has 2 carbons of acetyl CoA into 2 CO2 molecules, this process becomes much more difficult than adding the Acetyl group to a four carbon acid to form a six carbon acid (citrate). The citrate may then be sequentially oxidized to release two CO2 molecules.

Explanation: