Which statement best describes the oxidation of odd-chain fatty acids? The end products of the last cycle are propionyl CoA and Acetyl-CoA. One carbon is removed in one cycle. Hydroxy-fatty acids are produced. Additional specific enzymes are needed for the oxidation process compared to the process of oxidation of even-chain fatty acids.
The Correct Answer and Explanation is:
Correct Answer:
The end products of the last cycle are propionyl CoA and Acetyl-CoA.
Explanation
Fatty acid oxidation, specifically β-oxidation, is the process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH₂. This process differs slightly between even-chain and odd-chain fatty acids. While even-chain fatty acids are entirely converted into acetyl-CoA units, odd-chain fatty acids undergo a similar process with one key difference in the final step.
During β-oxidation of odd-chain fatty acids, the process removes two-carbon units as acetyl-CoA in successive cycles, just like even-chain fatty acids. However, because the number of carbon atoms is odd, the final cycle cannot yield two acetyl-CoA molecules. Instead, it produces one molecule of acetyl-CoA (2-carbon) and one molecule of propionyl-CoA (3-carbon).
Propionyl-CoA is then metabolized via a specialized pathway that converts it into succinyl-CoA, an intermediate of the citric acid cycle (Krebs cycle). This conversion requires biotin and vitamin B12 and involves a few additional enzymes, including propionyl-CoA carboxylase, methylmalonyl-CoA epimerase, and methylmalonyl-CoA mutase.
The other options in the question are incorrect:
- The statement “One carbon is removed in one cycle” is false; β-oxidation always removes two-carbon units per cycle as acetyl-CoA.
- The production of hydroxy-fatty acids is not a characteristic feature of odd-chain fatty acid oxidation.
- While additional enzymes are needed for the metabolism of propionyl-CoA, the oxidation itself proceeds similarly to that of even-chain fatty acids.
Therefore, the most accurate statement is: The end products of the last cycle are propionyl CoA and Acetyl-CoA.
