Question

During which stage in the complete oxidation of glucose is 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 $4$ ATP and $2NAD{H}_2$ molecules are formed. These $2NAD{H}_2$ 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 $2ATP,6NAD{H}_2$ and $2FAD{H}_2$ molecules are formed from two molecule 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 $3ATP$ and $2ATP$ molecules per $NAD{H}_2$ and $FAD{H}_2$ respectively.
Thus,
$4ATP$ are formed in glycolysis
$2ATP$ in Krebs cycle and
$34ATP$ from electron transport chain
$40ATP$
$2ATP$ molecules are used during glycolysis.
So, net gain of $ATP$ molecules during one complete oxidation of a glucose molecule is $38ATP$.