How many molecules of CO2 are produced directly from the citric acid cycle?

The citric acid cycle, also known as the Krebs cycle, is a crucial metabolic pathway that takes place in the mitochondria and is essential for energy production. During one complete turn of the cycle, two molecules of carbon dioxide (CO2) are released. This process begins with the conversion of acetyl-CoA into citrate, and as the cycle progresses, citrate undergoes several transformations.

Key steps in which CO2 is released include the decarboxylation reactions where isocitrate is converted into alpha-ketoglutarate and subsequently where alpha-ketoglutarate is converted into succinyl-CoA. Each of these steps involves the removal of a carbon atom in the form of CO2, leading to a total of two CO2 molecules produced for each turn of the cycle.

Thus, when considering the net production of CO2 directly from the citric acid cycle, the correct answer is that two molecules of CO2 are produced. This highlights the importance of the cycle not only in energy metabolism but also in the carbon balance of cellular respiration.