<P> Several of the citric acid cycle intermediates are used for the synthesis of important compounds, which will have significant cataplerotic effects on the cycle . Acetyl - CoA cannot be transported out of the mitochondrion . To obtain cytosolic acetyl - CoA, citrate is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol . There it is cleaved by ATP citrate lyase into acetyl - CoA and oxaloacetate . The oxaloacetate is returned to mitochondrion as malate (and then converted back into oxaloacetate to transfer more acetyl - CoA out of the mitochondrion). The cytosolic acetyl - CoA is used for fatty acid synthesis and the production of cholesterol . Cholesterol can, in turn, be used to synthesize the steroid hormones, bile salts, and vitamin D . </P> <P> The carbon skeletons of many non-essential amino acids are made from citric acid cycle intermediates . To turn them into amino acids the alpha keto - acids formed from the citric acid cycle intermediates have to acquire their amino groups from glutamate in a transamination reaction, in which pyridoxal phosphate is a cofactor . In this reaction the glutamate is converted into alpha - ketoglutarate, which is a citric acid cycle intermediate . The intermediates that can provide the carbon skeletons for amino acid synthesis are oxaloacetate which forms aspartate and asparagine; and alpha - ketoglutarate which forms glutamine, proline, and arginine . </P> <P> Of these amino acids, aspartate and glutamine are used, together with carbon and nitrogen atoms from other sources, to form the purines that are used as the bases in DNA and RNA, as well as in ATP, AMP, GTP, NAD, FAD and CoA . </P> <P> The pyrimidines are partly assembled from aspartate (derived from oxaloacetate). The pyrimidines, thymine, cytosine and uracil, form the complementary bases to the purine bases in DNA and RNA, and are also components of CTP, UMP, UDP and UTP . </P>

Nucleotides provide substrates for the citric acid cycle