TCA cycle means Tricarboxylic Acid Cycle. It is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins, acetyl-CoA, is the starting point for the TCA cycle, acetyl-CoA is the product of the reaction. Succinic acid (4C) undergoes oxidation to form Fumaric acid (4C) in the presence of enzyme Succinate dehydrogenase. The hydrogen released is accepted by coenzyme FAD (Flavin Adenine Dinucleotide) and it gets reduced to form ${\mathrm{F}\mathrm{A}\mathrm{D}\mathrm{H}}_2$ .

All enzymes required for Krebs' cycle are present in the mitochondrial matrix except succinate dehydrogenase. Succinate dehydrogenase enzyme is attached to the inner mitochondrial membrane.