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

Q. 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 CoA

(b) Electron transport chain

(c) Glycolysis

(d) Krebs cycle

Solution :

Correct option : B 
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.