Question

Which carbon moiety is released in each beta-oxidation cycle of even-numbered fatty acids?

• A. Five-carbon moiety
• B. Four-carbon moiety
• C. Three-carbon moiety
• D. Two-carbon moiety

Hint:

Fatty acids are broken down two carbons at a time during beta-oxidation, yielding acetyl-CoA which then directly feeds into the citric acid cycle.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Beta-oxidation is the primary catabolic pathway for fatty acids, occurring inside the mitochondria, where fatty acid chains are progressively broken down to generate metabolic energy.

Step 2: Detailed Explanation:
During each cycle of beta-oxidation, a fatty acyl-CoA molecule undergoes a series of four reactions: oxidation, hydration, oxidation, and thiolytic cleavage.
The cleavage occurs between the alpha and beta carbons (C-2 and C-3) of the fatty acid chain.
This reaction releases a terminal two-carbon moiety in the form of acetyl-CoA.
The remaining fatty acyl-CoA, now shortened by two carbons, enters the next cycle of beta-oxidation.
For an even-numbered saturated fatty acid, this cycle repeats until the entire chain is converted into acetyl-CoA units.

Step 3: Final Answer:
A two-carbon moiety (acetyl-CoA) is released during each beta-oxidation cycle.