Q.28 Determine the correctness or otherwise of the following Assertion [a] and the
Reason [r].
Assertion [a]: On a per carbon basis, palmitic acid yields more ATP than glucose.
Reason [r]: Carbons in palmitic acid are more reduced than those in glucose.
(A) Both [a] and [r] are true and [r] is the correct reason for [a]
(B) Both [a] and [r] are true but [r] is not the correct reason for [a]
(C) [a] is true but [r] is false
(D) [a] is false but [r] is true

Both Assertion [a] and Reason [r] are true, and [r] is the correct reason for [a]. The correct answer is (A).

Palmitic acid yields more ATP per carbon than glucose upon complete oxidation due to its more reduced carbon atoms, which release greater energy during oxidation to CO₂ and H₂O. This higher reduction state in fatty acids compared to carbohydrates explains the superior energy efficiency on a per-carbon basis.​

ATP Yield Calculations

Palmitic acid (C₁₆H₃₂O₂) undergoes β-oxidation, producing 8 acetyl-CoA, 7 NADH, and 7 FADH₂, yielding 131 ATP minus 2 for activation, for a net of 129 ATP (or ~106-108 ATP in some estimates using updated NADH/FADH₂ ratios of ~2.5/1.5 ATP). Glucose (C₆H₁₂O₆) yields ~32-38 ATP net via glycolysis, pyruvate oxidation, and TCA cycle.​

Per carbon:

• Palmitic acid: 129 ATP / 16 carbons ≈ 8.06 ATP/C

• Glucose: 32 ATP / 6 carbons ≈ 5.33 ATP/C (or 38/6 ≈ 6.33 ATP/C)

Thus, [a] is true.​

Oxidation State Comparison

Carbons in palmitic acid are more reduced, with oxidation states mostly -2 or -3 due to more C-H bonds (fewer oxygens: 2 O per 16 C). Glucose carbons average less reduced states (-1, 0, +1) with more C-O bonds (6 O per 6 C). More reduced carbons transfer more electrons to O₂ via ETC, generating extra FADH₂/NADH and thus more ATP.​

This directly causes higher ATP yield per carbon, making [r] true and the correct explanation for [a].

Option Analysis

• (A): Correct—Both true, [r] explains [a] via reduction driving electron flow and ATP.​

• (B): Incorrect—[r] is the direct biochemical reason (more electrons from reduced C → more reducing equivalents → more ATP).​

• (C): Incorrect—[r] is true (confirmed by oxidation states and O:C ratios).​

• (D): Incorrect—[a] is true (8.06 > 5.33-6.33 ATP/C).​

Introduction to Energy Yield in Metabolism

Palmitic acid ATP yield per carbon surpasses glucose due to more reduced carbons, a key concept in bioenergetics for CSIR NET Life Sciences. This assertion-reason question tests fatty acid oxidation efficiency versus carbohydrate metabolism. Understanding oxidation states clarifies why fats store more energy.​

Why Palmitic Acid Outperforms Glucose

Complete oxidation of palmitic acid (16 C) nets ~129 ATP via 7 β-oxidation cycles (7 NADH + 7 FADH₂ = 35 ATP) + 8 acetyl-CoA (96 ATP) – 2 activation. Glucose (6 C) nets 32 ATP. Per-carbon superiority (8 vs ~5 ATP/C) stems from fatty acids’ higher H:C ratio.​

• β-oxidation produces more FADH₂ (bypasses Complex I, but overall higher electrons).

• Fewer activation costs relative to carbons.

Role of Carbon Reduction State

Palmitic acid: C₁₆H₃₂O₂ (oxidation states -2/-3 for most C). Glucose: C₆H₁₂O₆ (+1/-1 average). Reduced C-H bonds release more energy oxidizing to CO₂.​

Implications for CSIR NET Preparation

This topic integrates biochemistry (β-oxidation, TCA), bioenergetics, and redox chemistry. Practice similar assertions on stearic acid or unsaturated fats.​