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Acetyl-CoA is a molecule that plays a crucial role in cellular metabolism. It is a thioester of coenzyme A and an acetyl group. This compound is central to the breakdown of carbohydrates, fats, and proteins, providing the primary fuel source for the citric acid cycle. In aerobic respiration, glucose is first broken down into pyruvate through glycolysis. Pyruvate then enters the mitochondria and is converted into acetyl-CoA by the pyruvate dehydrogenase complex. Similarly, fatty acids are broken down into acetyl-CoA through a process called beta-oxidation, and amino acids can also be catabolized to produce acetyl-CoA. Once formed, acetyl-CoA enters the citric acid cycle, also known as the Krebs cycle or TCA cycle, where it is oxidized to produce ATP, the cell's main energy currency, along with reduced electron carriers like NADH and FADH2. These electron carriers then go on to fuel the electron transport chain, generating even more ATP. Beyond energy production, acetyl-CoA is also a precursor for the synthesis of various biomolecules, including fatty acids, cholesterol, and neurotransmitters like acetylcholine. Its central position makes it a critical hub in cellular metabolism, linking catabolic and anabolic pathways.