Question

As someone already mentioned in one of the following questions, the TCA circuit generates GTP in addition to NADH and FADH2. The fate of NADH and FADH2 is clear: they are used to pump protons in the electron transfer system. Why is GTP, not ATP, produced in Gluconeogenesis & TCA Cycle? However, the fate of GTP seems less clearly described. I have seen a weak statement that 1 mol of GTP can produce 1 mol of ATP, but I do not know when, where, what, and how the energy of GTP is diverted to the production of ATP. So. My question;When, where, what and how GTP generated in the TCA circuit is used to generate ATP .

Answer 1

The GTP produced in the TCA cycle is converted to ATP in the mitochondrial matrix through a nucleoside diphosphate kinase reaction. This process of converting GTP to ATP is a part of substrate-level phosphorylation. The NADH and
`FADH_2` also produced in the TCA cycle contribute to ATP production through oxidative phosphorylation in the electron transport chain.

Step-by-step explanation:

The GTP generated in the TCA cycle is used to produce ATP through a nucleoside diphosphate kinase reaction where GTP donates a phosphate to ADP, forming ATP and GDP. This occurs in the mitochondrial matrix where the citric acid cycle also takes place. The enzyme involved in this reaction is succinate thiokinase, also known as succinyl-CoA synthetase. The GTP that is produced is equivalent to one ATP, and this transformation is a substrate-level phosphorylation event.

During the oxidative phosphorylation stage, NADH and
`FADH_2`generated in the TCA cycle transfer electrons to the electron transport chain (ETC), leading to the pumping of protons across the mitochondrial membrane and subsequently producing ATP through a gradient-driven mechanism known as chemiosmosis. The TCA cycle contributes to the total ATP yield from the catabolism of glucose by providing GTP, NADH, and
`FADH_2.`