Fatty acid synthesis is not directly activated in the way the question suggests; rather, fatty acids themselves are activated before they can undergo oxidation. The process described in the provided reference pertains to the activation and translocation of fatty acids for oxidation, not synthesis. Thus, the original question is misleading in its terminology and needs to be rephrased to address the activation of fatty acids for oxidation.
Rephrased Question: How Are Fatty Acids Activated for Oxidation?
Fatty acids are activated for oxidation through a two-step process that occurs in and around the mitochondria:
Step 1: Activation in the Outer Mitochondrial Membrane
- The process begins with the activation of a long-chain fatty acid in the outer mitochondrial membrane.
- This activation is catalyzed by the enzyme long-chain fatty acyl-CoA synthetase.
- This enzyme attaches a coenzyme A (CoA) molecule to the fatty acid, forming fatty acyl-CoA.
Step 2: Translocation into the Mitochondrial Matrix
- The fatty acyl-CoA molecule is too large to directly cross the inner mitochondrial membrane.
- A transport system involving carnitine palmitoyltransferase 1 (CPT1) and carnitine palmitoyltransferase 2 (CPT2) is needed.
- CPT1, located on the outer mitochondrial membrane, transfers the fatty acyl group from CoA to carnitine, forming fatty acyl-carnitine.
- The fatty acyl-carnitine is then transported across the inner mitochondrial membrane.
- CPT2, located on the inner mitochondrial membrane, transfers the fatty acyl group back to CoA, regenerating fatty acyl-CoA in the mitochondrial matrix.
Why is this activation necessary?
This activation process is crucial because:
- It enables fatty acids to enter the mitochondrial matrix, where beta-oxidation, the process that breaks down fatty acids for energy, takes place.
- The attachment of CoA essentially "tags" the fatty acid for metabolism.
Summary Table
| Step | Location | Enzyme | Reaction | Result |
|---|---|---|---|---|
| 1. Fatty Acid Activation | Outer Mitochondrial Membrane | Long-chain fatty acyl-CoA synthetase | Fatty acid + CoA → Fatty acyl-CoA | Fatty acyl-CoA ready for transport |
| 2. Fatty Acyl-CoA Transport (CPT1) | Outer Mitochondrial Membrane | Carnitine palmitoyltransferase 1 (CPT1) | Fatty acyl-CoA + Carnitine → Fatty acyl-carnitine + CoA | Fatty acyl-carnitine for membrane transport |
| 3. Translocation Through Inner Membrane | Inner Mitochondrial Membrane | Fatty acyl-carnitine Transporter | Transport through inner membrane | Fatty acyl-carnitine in matrix |
| 4. Fatty Acyl-CoA Transport (CPT2) | Inner Mitochondrial Membrane | Carnitine palmitoyltransferase 2 (CPT2) | Fatty acyl-carnitine + CoA → Fatty acyl-CoA + Carnitine | Fatty acyl-CoA ready for beta-oxidation |
