Question

The number of ATP molecules produced by the electron transport system from Krebs cycle intermediates in a single turn is

• A. 11
• B. 14
• C. 12
• D. 16

Answer 1

Answer: (C)

12

A single turn of Krebs cycle produces 3 molecules of reduced coenzyme $NAD{H}_2$ and 1 molecule of reduced $FAD{H}_2$ besides 1 molecule of GTP is synthesized directly through substrate level phosphorylation. The reduced coenzymes ( $NAD{H}_2$ and FAD$H_2$) are oxidised by mitochondrial electron transport system in the inner mitochondrial membrane. 3 molecules of ATP are synthesized when one molecule of $NAD{H}_2$ is oxidised and 2 molecules of ATP are synthesized when one molecule of $FAD{H}_2$ is oxidised. Thus the total ATP produced on oxidation of reduced coenzymes produced in one turn of Krebs cycle are (3x3) + (2x1) + 1 i.e., 12 ATP molecules.