Source:http://linkedlifedata.com/resource/umls/id/C1510758
NCI: Acetyl-CoA is produced in mitochondria through the metabolism of fatty acids and the oxidation of pyruvate to acetyl-CoA. When ATP is needed, this acetyl-CoA can enter the Krebs cycle to drive oxidative phosphorylation. When ATP supplies are abundant, the acetyl-CoA can be diverted to other purposes like energy storage in the form of fatty acids. The biosynthesis of fatty acids from this acetyl-CoA cannot take place directly however, since it is produced inside mitochondria while fatty acid biosynthesis occurs in the cytosol. Also, there is not a mechanism that directly transports acetyl-CoA out of mitochondria. To be transported, the acetyl-CoA must be chemically converted to citric acid using a pathway called the tricarboxylate transport system. Inside mitochondria, the enzyme citrate synthase joins acetyl-CoA with oxaloacetate to make citrate. This citrate is transported from the mitochondria to the cytosol, thus transporting the acetyl-CoA in the form of citrate. Once in the cytosol, the citrate is c