Question

How many cycles of $\beta$-oxidation are required for the complete oxidation of activated Oleic acid, 18 : 1 $(\Delta^{9})$?

• A. 5 Cycles \
• B. 7 Cycles \
• C. 8 Cycles \
• D. 6 Cycles

Hint:

To find the number of $\beta$-oxidation loops, divide the total carbon count by 2 and subtract 1. Unsaturation affects energy yield, but not the number of cuts needed.

Answer 1

The Correct Option is C

Step 1: Concept $\beta$-oxidation is the metabolic pathway by which fatty acyl-CoA molecules are broken down in the mitochondria to generate acetyl-CoA, NADH, and $\text{FADH}_{2}$. Each cycle cleaves a two-carbon unit from the carboxyl end of the fatty acid chain.

Step 2: Meaning Oleic acid is a monounsaturated fatty acid containing 18 carbon atoms and a single double bond at carbon position 9 ($18:1\,\Delta^{9}$). Complete oxidation means chopping the entire chain into 2-carbon acetyl-CoA pieces.

Step 3: Analysis * For a straight-chain saturated fatty acid with $n$ carbon atoms, the number of $\beta$-oxidation cycles required is calculated using the formula: $$\text{Cycles} = \frac{n}{2} - 1$$ * For an 18-carbon fatty acid chain: $$\text{Cycles} = \frac{18}{2} - 1 = 9 - 1 = 8\text{ cycles}$$ * The presence of the single double bond in oleic acid requires an auxiliary enzyme (enoyl-CoA isomerase) to shift the bond position during the pathway, but it does not alter the absolute total number of cleavage cycles required to split the 18 carbons into 9 fragments of acetyl-CoA.

Step 4: Conclusion Therefore, exactly 8 cycles of cleavage are needed to completely oxidize the activated oleic acid chain into 9 individual acetyl-CoA units. Final Answer: (C)