What is substrate level phosphorylation?

Substrate level phosphorylation is the process by which ATP is generated during glycolysis and the citric acid cycle. It occurs when a high-energy phosphate group from a substrate molecule is transferred directly to ADP to form ATP.

In glycolysis, substrate level phosphorylation occurs twice, once during the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate and again during the conversion of phosphoenolpyruvate to pyruvate. In the citric acid cycle, substrate level phosphorylation occurs during the conversion of succinyl-CoA to succinate.

Compared to oxidative phosphorylation, which generates the majority of ATP in cells, substrate level phosphorylation produces a smaller amount of ATP but does not require the use of an electron transport chain or a proton gradient across a membrane.

Overall, substrate level phosphorylation plays a crucial role in generating ATP during cellular respiration and providing a quick source of energy for cells.