Which processes involve substrate-level phosphorylation?

Which processes involve substrate-level phosphorylation?

• A. Glycolysis and oxidative phosphorylation
• B. Glycolysis and TCA cycle
• C. Oxidative phosphorylation only
• D. Glycolysis only

Answer: (D)

Substrate-level phosphorylation is the direct transfer of a phosphate from a high-energy substrate to ADP to form ATP, without using a proton gradient. In glycolysis, this happens twice: during the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate and again when phosphoenolpyruvate donates a phosphate to ADP to form pyruvate. In the tricarboxylic acid cycle, succinyl-CoA synthetase cleaves a thioester bond in succinyl-CoA and transfers the energy to GDP (or ADP) to make GTP (or ATP). By contrast, oxidative phosphorylation relies on the proton gradient to drive ATP synthesis via ATP synthase, not by transferring a phosphate from a substrate. So the processes that involve substrate-level phosphorylation are glycolysis and the TCA cycle.

Substrate-level phosphorylation is the direct transfer of a phosphate from a high-energy substrate to ADP to form ATP, without using a proton gradient. In glycolysis, this happens twice: during the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate and again when phosphoenolpyruvate donates a phosphate to ADP to form pyruvate. In the tricarboxylic acid cycle, succinyl-CoA synthetase cleaves a thioester bond in succinyl-CoA and transfers the energy to GDP (or ADP) to make GTP (or ATP). By contrast, oxidative phosphorylation relies on the proton gradient to drive ATP synthesis via ATP synthase, not by transferring a phosphate from a substrate. So the processes that involve substrate-level phosphorylation are glycolysis and the TCA cycle.