Which is correct for catabolism of 18 C fatty acid?

Options

A. Mitochondria, beta oxidation, 148 ATP molecules
B. Mitochondria, beta oxidation, 140 ATP molecules
C. Cytosol, beta oxidation, 146 ATP molecules
D. Cytosol, beta oxidation, 140 ATP molecules

Answer

To determine the correct statement regarding the catabolism of an 18-carbon fatty acid, we will break down the process into its essential steps:

### Step-by-Step Solution:

1. **Understanding Fatty Acid Structure**:
- An 18-carbon fatty acid consists of a long hydrocarbon chain with 18 carbon atoms.

2. **Initiation of Catabolism**:
- The catabolism of fatty acids begins with **beta-oxidation**, which occurs in the mitochondria. This process involves the breakdown of fatty acids into two-carbon units.

3. **Beta-Oxidation Process**:
- During beta-oxidation, the fatty acid undergoes a series of reactions that remove two carbon atoms at a time, converting them into **acetyl-CoA**. For an 18-carbon fatty acid, this process will yield 9 acetyl-CoA molecules (since 18/2 = 9).

4. **Oxidation of Acetyl-CoA**:
- The next step involves the oxidation of acetyl-CoA in the **Krebs cycle** (also known as the citric acid cycle). In this cycle, acetyl-CoA is further broken down, releasing carbon dioxide and transferring electrons to electron carriers.

5. **Electron Transport Chain**:
- The final stage of fatty acid catabolism is the **electron transport chain**, where the electrons carried by NADH and FADH2 (produced during beta-oxidation and the Krebs cycle) are transferred through a series of proteins in the inner mitochondrial membrane. This process generates ATP through oxidative phosphorylation.

6. **ATP Yield**:
- The complete oxidation of one molecule of an 18-carbon fatty acid yields a total of **148 ATP molecules**. This includes ATP produced during beta-oxidation, the Krebs cycle, and the electron transport chain.

7. **Conclusion**:
- Based on the above steps, the correct statement regarding the catabolism of an 18-carbon fatty acid is that it occurs in the mitochondria, involves beta-oxidation, and results in the formation of 148 ATP molecules.

### Final Answer:
The correct option regarding the catabolism of an 18-carbon fatty acid is that it occurs in the mitochondria, involves beta-oxidation, and produces a total of 148 ATP molecules.

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