The cycle that breaks down pyruvic acid into carbon dioxide and produces NADH, FADH2, and ATP is the Krebs cycle, also known as the citric acid cycle.

Here's a breakdown of the process:

1. Pyruvate Oxidation: Pyruvic acid, produced from glycolysis, is transported into the mitochondria. It undergoes oxidative decarboxylation, losing a carbon atom as CO2 and becoming acetyl-CoA. This process also generates NADH.

2. Citric Acid Cycle: Acetyl-CoA enters the Krebs cycle and combines with oxaloacetate to form citrate. Through a series of eight enzymatic reactions, the citrate molecule is progressively oxidized, releasing two CO2 molecules per cycle. In the process, electrons are extracted and used to reduce NAD+ to NADH and FAD to FADH2. Additionally, some ATP is directly produced through substrate-level phosphorylation.

Key Points:

* Location: The Krebs cycle takes place in the mitochondrial matrix.

* Energy Carriers: NADH and FADH2 carry electrons to the electron transport chain, which is the primary energy-producing pathway in cellular respiration.

* ATP Production: The Krebs cycle produces a small amount of ATP directly (one molecule per cycle), but its main contribution is the generation of electron carriers (NADH and FADH2) that fuel ATP synthesis in the electron transport chain.

* Carbon Dioxide Production: The Krebs cycle is a major source of CO2, which is released as a waste product during cellular respiration.

Overall, the Krebs cycle is a vital part of cellular respiration, playing a key role in the breakdown of glucose to extract energy and generate ATP.