Q.Do you know any step in the TCA cycle where there is substrate level phosphorylation. Which one?

Yes, the citric acid cycle has one clear substrate-level phosphorylation step.

• It occurs during the conversion of succinyl-CoA to succinic acid.
• This reaction directly generates a molecule of GTP. …

Most of the ATP eventually gained from the citric acid cycle comes indirectly, through the NADH and FADH2 it generates being oxidised later at the electron transport system. But the cycle also includes one reaction that produces an energy-rich phosphate compound directly, without involving electron transport at all.

This happens during the conversion of succinyl-CoA to succinic acid. As this step proceeds, a molecule of GTP is synthesised directly. Because this synthesis comes from transferring a phosphate group within the reaction itself rather than through a membrane-based electron transport chain, it counts as substrate-level phosphorylation, exactly analogous to the two substrate-level phosphorylation steps seen earlier in glycolysis. …

Method 1

1. Recall the TCA-cycle step converting succinyl-CoA to succinic acid.
2. Note this step directly generates GTP — a substrate-level phosphorylation, with no ETS/membrane involved. …