Which cycle produces CO2 from acetyl-CoA?

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is the correct choice for this question because it specifically involves the conversion of acetyl-CoA into carbon dioxide (CO2) as a major byproduct of cellular respiration. Acetyl-CoA, derived from carbohydrates, fats, and proteins, enters the Krebs cycle where it undergoes a series of enzymatic reactions.

During these reactions, acetyl-CoA combines with oxaloacetate to form citrate, which is then transformed through multiple steps back into oxaloacetate. Throughout the cycle, two molecules of CO2 are released for each acetyl-CoA that is oxidized. This means that the Krebs cycle plays a crucial role in energy production and is a key metabolic pathway through which cellular respiration extracts energy from food.

In contrast, glycolysis primarily breaks down glucose into pyruvate and does not produce CO2. The electron transport chain is focused on ATP production through the transfer of electrons and does not involve the conversion of acetyl-CoA to CO2. Fermentation occurs in the absence of oxygen and converts pyruvate into lactate or ethanol, without producing CO2 from acetyl-CoA.