Question

During which stage in the complete oxidation of glucose, are the greatest number of ATP molecules formed from ADP?

• A. Conversion of pyruvic acid to acetyl Co-A
• B. Electron transport chain
• C. Glycolysis
• D. Krebs cycle

Answer 1

Answer: (B)

In glycolysis, four ATP and two $NAD{H}_2$ molecules are formed. These two $NAD{H}_2$ molecules go to electron transport chain. In oxidative decarboxylation, no ATP molecule is formed but two molecules of $NAD{H}_2$ are formed from two molecules of pyruvate. These two $NAD{H}_2$ go to electron transport chain. In Krebs cycle, two ATP, six $NAD{H}_2$ and two molecules are formed from two molecules of acetyl Co-A. These $NAD{H}_2$ and $FAD{H}_2$ go to electron transport chain. In electron transport chain, all $NAD{H}_2$ and $FAD{H}_2$ pass to electron carriers and yield three ATP and two ATP molecules per $NAD{H}_2$ and $FAD{H}_2$ respectively. Thus, $4$ ATP are formed in glycolysis $2$ ATP in Krebs cycle and $34$ ATP from electron transport chain $40$ ATP Two ATP molecules are used during glycolysis. So, net gain of ATP molecules during one complete oxidation of a glucose molecule is $38$ ATP.