Question

Substrate Level Phosphorylation results in the production of ATP molecules.
During which of the following processes does substrate level phosphorylation occur?
1. Glycolysis
II. Krebs Cycle
III. Electron Transport Chain

• A. I only
• B. II only
• C. III only
• D. I and II only
• E. II and III only

Answer 1

Answer: (D)

I and II only

Substrate level phosphorylation is the formation of ATP by the direct transfer of phosphate group to ADP. There are total three reactions in respiration where substrate level phosphorylation occurs, two in glycolysis and one in krebs cycle. The reactions are:

1. In glycolysis:

(i) When 1,3-bisphosphoglycerate (BPG) is converted into 3-phosphoglycerate (3PG) by the enzyme Phosphoglcerate kinase.

(ii) When Phosphoenolpyruvate (PEP) is converted into pyruvate by the enzyme Pyruvate kinase.

2. In krebs cycle:

(i) When Succinyl-CoA is converted into Succinate by the enzyme Succinate thiokinase.

Hence, substrate level phosphorylation occurs in Glycolysis and Krebs cycle.

So, the correct answer is 'I and II only'.