Question

Substrate-level phosphorylation does not occur in the following reactions of aerobic respiration:

• A. 1,3 bisphosphoglyceric acid → 3 phosphoglyceric acid
• B. 3 phosphoglyceric acid → 2 phosphoglyceric acid
• C. Phosphoenol pyruvic acid → Pyruvic acid
• D. Succinyl CoA → Succinic acid

Hint:

Substrate-level phosphorylation occurs in glycolysis and the Krebs cycle, generating ATP without an electron transport chain.

Answer 1

The Correct Option is B

Step 1: Understanding Substrate-Level Phosphorylation
Substrate-level phosphorylation (SLP) is a process in which a phosphate group is directly transferred from a high-energy substrate to ADP, forming ATP. This occurs in glycolysis and the Krebs cycle.
Step 2: Analyzing the Reactions
- 1,3-bisphosphoglyceric acid → 3-phosphoglyceric acid:
Substrate-level phosphorylation occurs here (ATP is generated).
- 3-phosphoglyceric acid → 2-phosphoglyceric acid:
This is a simple isomerization reaction and does not involve ATP formation.
- Phosphoenol pyruvate → Pyruvic acid:
ATP is generated via substrate-level phosphorylation.
- Succinyl CoA → Succinic acid:
ATP (or GTP) is generated in this step via substrate-level phosphorylation.
Thus, the reaction where substrate-level phosphorylation does not occur is option (B).