Question

Although rare, mutations in citric acid cycle enzymes have been documented. Defective ?-ketoglutarate dehydrogenase, succinyl-CoA synthetase, and succinate dehydrogenase typically affect the central nervous system and result in movement disorders and neurodegeneration. In addition, mutations in fumarase and isocitrate dehydrogenase have been linked to carcinogenesis.

(A) Why do mutations in this pathway have such severe consequences?

(B) Why would a deficiency in succinate dehydrogenase lead to a shortage of free coenzyme A?

(C) How would a fumarase deficiency affect the levels of pyruvate, fumarate, and malate in cells?