A fatty acid with 14 carbon atoms will undergo how many cycles of beta-oxidation?

Question

BlackTom AI · Accepted Answer

Beta-oxidation removes two carbon units (as acetyl-CoA) from the carboxyl end of a saturated even-chain fatty acid each cycle. Key points: each cycle shortens the chain by 2 carbons; the total number of acetyl-CoA molecules produced from an even-numbered saturated fatty acid of n carbons is n/2; the number of beta-oxidation cycles required equals the number of acetyl-CoA produced minus 1 because the final cleavage yields two acetyl-CoA in the last step.

Step-by-step reasoning and calculations:
1. Assume a saturated even-chain fatty acid with n = 14 carbons.
2. Calculate total acetyl-CoA molecules produced: n/2 = 14/2 = 7 acetyl-CoA.
   - Intermediate: 14 carbons → 7 × 2-carbon acetyl-CoA units.
3. Determine number of beta-oxidation cycles:
   - Each cycle produces one acetyl-CoA and shortens the chain by 2 carbons, but the final cycle cleaves the remaining 4-carbon fragment into two acetyl-CoA in one last cleavage, so cycles = (number of acetyl-CoA) − 1.
   - cycles = 7 − 1 = 6 cycles.

Why this is correct:
- Conceptually, after 6 cycles removing 2 carbons each, 12 carbons have been removed leaving a 2-carbon unit that, together with the last cleavage, yields the final acetyl-CoA pair, totaling 7 acetyl-CoA. The formula (n/2) − 1 for even saturated fatty acids gives the correct cycle count.

Why the other choices are incorrect:
- a. 7 cycles: would imply one cycle per acetyl-CoA produced, but the final cleavage produces two acetyl-CoA in the last reaction, so cycles are one fewer.
- b. 4 cycles and d. 5 cycles: these undercount the required cleavages; they would not reduce a 14-carbon chain fully to acetyl-CoA units.

Conclusion: A 14-carbon fatty acid undergoes 6 cycles of beta-oxidation, matching the provided correct answer (c. 6 cycles).

A fatty acid with 14 carbon atoms will undergo how many cycles of beta-oxidation?单项选择题

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