Which of the following is the best description of substrate-level phosphorylation in glycolysis?

• A. The transfer of electrons from glucose to oxygen, producing water.
• B. The direct transfer of a phosphate group from a phosphorylated substrate to ADP, forming ATP.
• C. The oxidation of NADH to NAD\(^+\) coupled with ATP synthesis.
• D. The generation of ATP using a proton gradient across the mitochondrial membrane.

Answer: (B)

Verified step by step guidance

1. Understand the concept of substrate-level phosphorylation: It is a process where a phosphate group is directly transferred from a phosphorylated substrate to ADP to form ATP, without the involvement of an electron transport chain or a proton gradient.
2. Review the context of glycolysis: Glycolysis is a metabolic pathway that occurs in the cytoplasm and involves the breakdown of glucose into pyruvate, producing ATP and NADH in the process.
3. Identify the key feature of substrate-level phosphorylation in glycolysis: This process occurs during specific steps of glycolysis, such as when phosphoenolpyruvate (PEP) donates a phosphate group to ADP to form ATP.
4. Eliminate incorrect options: For example, the transfer of electrons from glucose to oxygen producing water describes oxidative phosphorylation, not substrate-level phosphorylation. Similarly, the generation of ATP using a proton gradient across the mitochondrial membrane refers to chemiosmosis, not glycolysis.
5. Select the correct description: The direct transfer of a phosphate group from a phosphorylated substrate to ADP, forming ATP, is the best description of substrate-level phosphorylation in glycolysis.