Q.95 Glucose and hexanoic acid, each having six carbon atoms can undergo complete biological
oxidation. In terms of net ATP generation, which of the following statements is CORRECT?
(A) Glucose produces more ATP than hexanoic acid
(B) Only glucose can generate ATP
(C) Both glucose and hexanoic acid produce same amount of ATP
(D) Hexanoic acid produces more ATP than glucose
Hexanoic acid generates more net ATP than glucose despite both having six carbons, due to fatty acids’ higher energy density from beta-oxidation producing more reducing equivalents (NADH/FADH2).
Glucose yields ~30-32 ATP; hexanoic acid yields ~48-52 ATP via efficient fat catabolism.
Correct Answer
(D) Hexanoic acid produces more ATP than glucose
Option Analysis
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(A) Glucose produces more ATP than hexanoic acid: Incorrect—glucose glycolysis nets 2 ATP + 2 NADH, TCA cycle yields 2 GTP + 8 NADH + 2 FADH2 (total ~30-32 ATP); fats generate more reducing equivalents per carbon.
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(B) Only glucose can generate ATP: False—both substrates feed oxidative phosphorylation; fatty acids via beta-oxidation → acetyl-CoA → TCA, producing substantial ATP.
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(C) Both glucose and hexanoic acid produce same amount of ATP: Wrong—same C6 doesn’t mean equal energy; hexanoic acid (C6H12O2) activation costs 2 ATP but beta-oxidation of 3 acetyl-CoA units + extra FADH2 gives ~48-52 ATP vs. glucose’s 30-32.
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(D) Hexanoic acid produces more ATP than glucose: Correct—Hexanoic acid undergoes 2 beta-oxidation cycles (4 NADH + 1 FADH2 + 3 acetyl-CoA), TCA yields 24 ATP equivalents + ETC from reducers = 48-52 total ATP vs. glucose’s lower yield.
ATP Yield Calculation
Glucose (C6H12O6): Glycolysis (2 ATP + 2 NADH) + 2 pyruvate → 2 acetyl-CoA (2 NADH) + 2 TCA cycles (6 NADH + 2 FADH2 + 2 GTP) = ~30-32 ATP.
Hexanoic acid (C6H12O2): Activation (-2 ATP) + 2 β-ox cycles (2 NADH + 2 FADH2) + 3 acetyl-CoA → TCA (24 ATP equiv.) = ~48-52 ATP.
Glucose Hexanoic Acid ATP: Fats Win Energy Yield
Glucose hexanoic acid ATP comparison reveals why fats excel as energy storage. Despite identical C6 formulas, hexanoic acid yields 48-52 ATP vs. glucose’s 30-32 through beta-oxidation’s FADH2-rich pathway.
Yield Breakdown
| Substrate | Pathway | Net ATP | Why? |
|---|---|---|---|
| Glucose | Glycolysis + TCA | 30-32 | Oxygen-heavy, fewer reducers |
| Hexanoic acid | β-oxidation + TCA | 48-52 | More NADH/FADH2 per carbon |
| Difference | Fats 60% more efficient | +18-22 ATP | Hydrophobic storage bonus |
Glucose hexanoic acid ATP math proves evolutionary fat preference. Beta-oxidation generates 3 acetyl-CoA + extra FADH2 from acyl-CoA dehydrogenase, maximizing ETC proton pumping.
GATE Prep Insights
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Hexanoic: CH3(CH2)4COOH → 2 β-ox (4 NADH + 2 FADH2) + 3 acetyl-CoA.
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Glucose: C6 → 2 pyruvate → 2 acetyl-CoA (less FADH2).
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Key: Fats ~9 kcal/g vs. carbs 4 kcal/g; test reducing equivalents.
