Final answer:
GTP or ATP is produced during the conversion of succinyl-CoA to succinate in the citric acid cycle, involving an enzyme-catalyzed reaction that generates a high-energy phosphate.
Step-by-step explanation:
GTP or ATP is produced during the conversion of succinyl-CoA to succinate. This is the only step in the citric acid cycle that directly generates a molecule of high-energy phosphate.
In the enzymatic conversion of succinyl-CoA to succinate, the high-energy bond of succinyl-CoA is broken, and this energy is used to form GTP from GDP and inorganic phosphate. This GTP can then be used to generate ATP, which means that the production of GTP is equivalent to the production of ATP.
The overall reaction that leads to the production of GTP (and subsequently ATP) in the citric acid cycle is catalyzed by the enzyme succinyl-CoA synthetase. This is a two-step reaction where a phosphate group replaces the -S-CoA group to initially form succinyl phosphate and then the transfer of this phosphate group to GDP, generating GTP.