Q.44 The number of cycles required for complete degradation of Palmitic acid (16 Carbon) by
β-oxidation is __________.
Palmitic acid, a 16-carbon saturated fatty acid, requires 7 cycles of β-oxidation for complete degradation. Each cycle removes 2 carbons as acetyl-CoA, leaving the final pair as the 8th acetyl-CoA without an additional cycle.
β-Oxidation Process
β-Oxidation occurs in mitochondria after fatty acid activation to acyl-CoA and transport via carnitine shuttle. Four enzymatic steps per cycle—dehydrogenation (FADH₂), hydration, oxidation (NADH), and thiolysis—shorten the chain by 2 carbons. For palmitoyl-CoA (C16), initial chain length demands repeated cycles until only acetyl-CoA (C2) remains.
Cycle Calculation
General formula: (n/2) – 1 cycles, where n = total carbons. For palmitic acid, n=16, so (16/2) – 1 = 7 cycles. This yields 8 acetyl-CoA: 7 from cycles + 1 final unit. Each cycle produces 1 NADH and 1 FADH₂ for ATP generation via electron transport.
Common Exam Distractors
Exams like CSIR NET test misconceptions. 8 cycles wrongly assumes a cycle for the last acetyl-CoA. 6 or fewer ignores full 16C breakdown. Activation costs 2 ATP equivalents but does not affect cycle count. Fill-in-the-blank expects 7; no options provided, but 7 matches standard derivation.
Energy Yield Context
7 cycles generate 7 NADH (21 ATP), 7 FADH₂ (14 ATP), plus 8 acetyl-CoA (96 ATP via TCA), totaling 131 ATP before subtracting 2 for activation, netting 129 ATP. This underscores why precise cycle counting matters for bioenergetics questions in competitive exams.
