Fatty acids are not directly oxidized; they undergo a process to prepare them for oxidation. The process detailed in the provided reference focuses on a method for producing fatty acids from alkanes rather than how they are prepared within the body for oxidation. Therefore, we will rephrase the question to be "How are fatty acids prepared for oxidation inside the body?" to accurately reflect the answer.
Before fatty acids can be used to produce energy via oxidation, they must undergo activation and transport. Here's a breakdown of the steps:
Activation of Fatty Acids
Fatty acids must be activated before they can enter the mitochondria for oxidation.
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Step 1: Conversion to Fatty Acyl-CoA: The fatty acid reacts with coenzyme A (CoA) in a reaction catalyzed by fatty acyl-CoA synthetase. This reaction uses ATP and forms fatty acyl-CoA, a high-energy thioester. This activation step happens in the cytosol.
- Example: Palmitic acid + CoA + ATP → Palmitoyl-CoA + AMP + PPi
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Purpose of Activation: The attachment of CoA is critical; it creates an activated form that can now be transported across the mitochondrial membrane.
Transport into the Mitochondria
Once activated, fatty acyl-CoA must be transported into the mitochondria, where oxidation takes place.
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The Carnitine Shuttle: Fatty acyl-CoA cannot directly cross the inner mitochondrial membrane. It requires a carrier system called the carnitine shuttle.
- Step 1: Formation of Acyl-Carnitine: The acyl group of fatty acyl-CoA is transferred to carnitine, forming acyl-carnitine, through the action of carnitine palmitoyltransferase I (CPT I), which is located on the outer mitochondrial membrane.
- Step 2: Translocation: Acyl-carnitine is transported across the inner mitochondrial membrane by a specific transporter, carnitine-acylcarnitine translocase.
- Step 3: Regeneration of Fatty Acyl-CoA: On the matrix side of the membrane, carnitine palmitoyltransferase II (CPT II) transfers the acyl group back to CoA, regenerating fatty acyl-CoA in the mitochondrial matrix.
- Step 4: Return of Carnitine: The carnitine returns to the cytosolic side of the membrane to repeat the process.
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Why is this Transport Necessary?: The mitochondrial membrane is impermeable to fatty acyl-CoA, necessitating the shuttle system for proper oxidation.
Summary Table: Fatty Acid Preparation for Oxidation
| Stage | Location | Key Reaction | Purpose |
|---|---|---|---|
| Activation | Cytosol | Fatty Acid + CoA + ATP → Fatty Acyl-CoA + AMP + PPi | Convert fatty acid to activated form, ready for transport |
| Carnitine Shuttle | Mitochondrial Membranes | Acyl-CoA + Carnitine → Acyl-Carnitine + CoA | Facilitate the passage of activated fatty acids into the mitochondrial matrix |
| Reactivation | Mitochondrial Matrix | Acyl-Carnitine + CoA → Acyl-CoA + Carnitine | Reform Fatty Acyl-CoA in the matrix for oxidation |
Reference Information:
The provided reference discusses a method for synthesizing fatty acids using alkanes as a starting material, as a completely different approach than how fatty acids are prepared for oxidation within biological systems:
"A process for producing fatty acids from C 20 to C 30 normal alkanes by air oxidizing the alkanes, followed by hydrogenating the product of the air oxidation and then oxidizing the hydrogenated product by nitric acid oxidation. The crude fatty acid product may be purified by a second hydrogenation to convert ni."
This highlights an industrial process, not a biological one, and does not apply to the original question of how fatty acids are prepared within the body for oxidation.
In summary, fatty acids are prepared for oxidation by being activated in the cytosol by conversion to fatty acyl-CoA. This activated form then must use the carnitine shuttle to be transported across the mitochondrial membrane where it can be re-converted to fatty acyl-CoA in the mitochondrial matrix.
