


For the most part, the major foodstuffs (Cellular respiration consists of three metabolic processes: glycolysis, the tricarboxylic acid cycle (TCA cycle; also known as the Krebs, or citric acid, cycle), and oxidative phosphorylation (respiratory-chain phosphorylation). Glucose and other organic fuel molecules from carbohydrates, fats, and proteins ) are made available for the energy-yielding process by degradation to a two-carbon fragment (acetyl group) that, when combined are broken down during glycolysis. Energy released during glycolysis is captured in ATP. In the presence of oxygen, molecules of pyruvate (pyruvic acid) produced during glycolysis enter the mitochondria, where they are each converted into a compound known as acetyl coenzyme A, provides the fuel for an important sequence of metabolic reactions called the tricarboxylic acid cycle (TCA cycle)which then enters the TCA cycle.
