The common metabolite to the respiration-mediated breakdown of fats, carbohydrates, and proteins is acetyl-CoA.
Acetyl-CoA is a key intermediate in cellular metabolism and serves as the entry point for the citric acid cycle (also known as the Krebs cycle) in aerobic respiration. It is produced through the breakdown of various macronutrients:
- Fats: Fatty acids are broken down through beta-oxidation, producing acetyl-CoA molecules.
- Carbohydrates: Glucose, the primary carbohydrate fuel for cells, undergoes glycolysis, producing pyruvate. Pyruvate is then converted to acetyl-CoA before entering the citric acid cycle.
- Proteins: Proteins are broken down into amino acids, some of which can be converted to intermediates that enter the citric acid cycle as acetyl-CoA. This conversion involves removing the amino group from the amino acid, producing a compound that can be further metabolized to generate acetyl-CoA.
Once acetyl-CoA is formed, it enters the citric acid cycle, where it undergoes a series of reactions to produce energy in the form of ATP and reducing equivalents such as NADH and FADH2, which are used in oxidative phosphorylation to generate more ATP.