The Krebs cycle also occurs in the matrix of the mitochondria. Acetyl coA reacts with 4-carbon oxaloacetate to form 6-carbon citrate and coA is released.Citrate undergoes decarboxylation and dehydrogenation to form 5-carbon alpha ketoglutarate (αKG). Carbon dioxide is released and NAD is reduced.αKG undergoes decarboxylation and dehydrogenation to form 4-carbon compound (succinyl coA). Carbon dioxide is released and NAD is reduced.The 4-carbon compound is converted back into 4-carbon oxaloacetate in 4 steps. ATP is made and FAD and then NAD is reduced in the process.