In glycolysis, substrate-level phosphorylation refers to the direct synthesis of ATP by transfer of a phosphate group from a high-energy intermediate to ADP. Which pair of glycolytic reactions produces ATP via substrate-level phosphorylation?

• A. Glucose → glucose-6-phosphate and fructose-6-phosphate → fructose-1,6-bisphosphate
• B. Fructose-1,6-bisphosphate → glyceraldehyde-3-phosphate + dihydroxyacetone phosphate and 2-phosphoglycerate → phosphoenolpyruvate
• C. Glyceraldehyde-3-phosphate → 1,3-bisphosphoglycerate and pyruvate → lactate
• D. 1,3-bisphosphoglycerate → 3-phosphoglycerate and phosphoenolpyruvate → pyruvate

Answer: (D)

Verified step by step guidance

1. Recall that substrate-level phosphorylation in glycolysis involves the direct transfer of a phosphate group from a high-energy intermediate to ADP, forming ATP without the involvement of the electron transport chain.
2. Identify the glycolytic intermediates known to have high-energy phosphate bonds capable of donating a phosphate group directly to ADP. These are 1,3-bisphosphoglycerate and phosphoenolpyruvate.
3. Recognize the specific reactions where these intermediates transfer their phosphate groups to ADP: 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate, and phosphoenolpyruvate is converted to pyruvate.
4. Understand that these two reactions each produce one molecule of ATP per molecule of substrate, making them the key substrate-level phosphorylation steps in glycolysis.
5. Conclude that the pair of reactions producing ATP via substrate-level phosphorylation are: 1,3-bisphosphoglycerate \(\rightarrow\) 3-phosphoglycerate and phosphoenolpyruvate \(\rightarrow\) pyruvate.