The phosphate group is transferred to GDP to form GTP and succinic acid. The dehydrogenase that catalyzes this reaction is bound to the inner mitochondrial membrane. Water is added to fumaric acid which rearranges its chemical bonds to form malic acid. Malic acid is oxidized and NAD is reduced. A molecule of NADH is produced.
Oxaloacetic acid is regenerated to begin the cycle again.
Two different carbons leave as carbon dioxide. One ATP molecule is produced by substrate level phosphorylation. Oxaloacetic acid is regenerated. For every glucose molecule split during glycolysis, two acetyl fragments are produced. Thus, it takes two turns of the cycle to complete the oxidation of glucose.