Question

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

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

Answer 1

Answer: (C)

Electron transport chain

In glycolysis 4 ATP and 2NADH2 molecules are formed. These 2NADH2 molecules go to electron transport chain. In oxidative decarboxylation no ATP molecule is formed but two molecules of 2NADH2 are formed from two molecules of pyruvate. These two NADH2 go to electron transport chain. In Kreb's cycle 2 ATP, 6NADH2 and 2FADH2 molecules are formed from two molecule of acetyl Co-A. These NADH2 and 2FADH2 go to electron transport chain. In electron transport chain all 2NADH2 and 2FADH2 pass to electron carriers and yield 3 ATP and 2 ATP molecules per 2NADH2 and 2FADH2 respectively. Thus, 4 ATP are formed in glycolysis, 2 ATP in Krebs cycle and 34 ATP from electron transport chain. 40 ATP and 2 ATP molecules are used during glycolysis. So, net gain of ATP molecules during one complete oxidation of a glucose molecule is 38 ATP.

So, the correct answer is 'Electron transport chain'.