Question

Substrate-level ATP gain during complete oxidation of 1 molecule of glucose is

• A. 8 ATP
• B. 6 ATP
• C. 4 ATP
• D. 2 ATP

Answer 1

Answer: (C)

4 ATP

In substrate-level phosphorylation, the involved organic compound itself serves as both electron donor (becomes oxidized) and an electron acceptor (becomes reduced) and its high energy phosphate bonds are transferred to ADP to form ATP.

• During glycolysis, the enzyme phosphoglycerate kinase transfers the high energy phosphoryl group from the carboxyl group of 1, 3- bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate.
  
• During glycolysis, the enzyme pyruvate kinase transfers the high energy phosphoryl group from phosphoenolpyruvate to ADP, forming ATP and pyruvate.
  
• During TCA cycle (Citric acid cycle; Kreb’s cycle), the enzyme succinyl-CoA synthetase breaks the thioester bond of succinyl-CoA and the energy released in this breakage is used to drive the synthesis of a phosphoanhydride bond in 2 GTP or 2 ATP. Succinate is the product in the process.
  
• So the correct option is '4 ATP'.