Question

Substrate level phosphorylation occurs during which step of Krebs' cycle?

• A. Succinyl $CoA\to$ Succinic acid
• B. Isocitric acid $\to$ Oxalosuccinic acid
• C. Oxalosuccinic acid $\to \alpha$-ketoglutaric acid
• D. Malic acid $\to OAA$

Answer 1

Answer: (A)

During Krebs' or citric acid cycle, succinyl-$CoA$ is acted upon by enzyme succinyl-CoA synthetase to form succinate (a $4C$ compound). The reaction releases sufficient energy to form $ATP$ (in plants) or $GTP$ (in animals) by substrate level phosphorylation. $GTP$ can form $ATP$ through a coupled reaction.