BackStudy Notes on β-Oxidation of Fatty Acids
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β-Oxidation of Fatty Acids
Intermediates of β-Oxidation
β-Oxidation is the metabolic process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH2. The process involves several key intermediates.
Key Intermediate: 3-hydroxyacyl-CoA is one of the main intermediates formed during β-oxidation.
General Steps:
Fatty acyl-CoA is oxidized to trans-Δ2-enoyl-CoA.
Hydration forms 3-hydroxyacyl-CoA.
Oxidation yields 3-ketoacyl-CoA.
Thiolysis releases acetyl-CoA and a shortened acyl-CoA.
Example: For palmitoyl-CoA (C16:0), the process repeats until the entire chain is converted to acetyl-CoA units.
Reduction of C=C Double Bonds During β-Oxidation
Some unsaturated fatty acids require additional steps during β-oxidation due to the presence of double bonds. NADPH is needed to reduce certain double bonds that cannot be processed by the standard enzymes.
Key Point: NADPH is required to reduce a cis double bond to a trans configuration, which is compatible with the β-oxidation pathway.
Specific Conformation: The enzyme enoyl-CoA isomerase converts cis-Δ3 double bonds to trans-Δ2 double bonds, but some configurations require 2,4-dienoyl-CoA reductase and NADPH.
Example: Linoleic acid (18:2) requires NADPH for the reduction of its double bonds during β-oxidation.
β-Oxidation of a Fatty Acid: Example Calculation
Consider the β-oxidation of a saturated fatty acid, such as palmitic acid (C16:0).
Number of Rounds: The number of β-oxidation cycles required is n - 1, where n is the number of carbons divided by 2 for acetyl-CoA formation.
For palmitic acid (C16:0): 7 rounds of β-oxidation are needed to yield 8 acetyl-CoA.
Products per Round:
Each round produces 1 FADH2, 1 NADH, and 1 acetyl-CoA (except the final round, which yields 2 acetyl-CoA).
ATP Yield Calculation:
Each FADH2 yields approximately 1.5 ATP.
Each NADH yields approximately 2.5 ATP.
Each acetyl-CoA enters the citric acid cycle, producing 10 ATP per cycle.
Example Calculation for Palmitic Acid (C16:0):
7 FADH2 × 1.5 ATP = 10.5 ATP
7 NADH × 2.5 ATP = 17.5 ATP
8 acetyl-CoA × 10 ATP = 80 ATP
Total ATP yield: 108 ATP (minus 2 ATP for activation)
Summary Table: β-Oxidation Products
Product | Per Round | Total (for C16:0) | ATP Yield |
|---|---|---|---|
FADH2 | 1 | 7 | 10.5 |
NADH | 1 | 7 | 17.5 |
Acetyl-CoA | 1 (last round yields 2) | 8 | 80 |
Additional info: The ATP yield may vary slightly depending on the cell type and mitochondrial efficiency. The process is essential for energy production, especially during fasting or prolonged exercise.
