**Question:** Long chain fatty acid is transported into inner mitochondria membrane by

A. Carnitine palmitoyltransferase 1 (CPT1)
B. Fatty acid translocase (FAT/CD36)
C. Monoacylglycerol lipase (MGL)
D. Mitochondrial inner membrane proteins

**Core Concept:** Mitochondria are the powerhouses of cells, where fatty acids are oxidized to produce energy in the form of adenosine triphosphate (ATP) via a process called β-oxidation. Long-chain fatty acids cannot passively diffuse across the inner mitochondrial membrane due to its selective permeability. Instead, they require specific transporters to enter the mitochondria.

**Why the Correct Answer is Right:** Long-chain fatty acids, particularly those with 12-20 carbons, are transported into the inner mitochondrial membrane via two primary proteins:

1. **A. Carnitine palmitoyltransferase 1 (CPT1):** CPT1 is a key enzyme in the process of fatty acid transport into mitochondria. It catalyzes the first rate-limiting step of the process, converting acylcarnitine to acyl-CoA and carnitine. CPT1 has three isoforms: CPT1A, CPT1B, and CPT1C, with CPT1A and CPT1B being the main isoforms in the liver and muscle respectively.

2. **B. Fatty acid translocase (FAT/CD36):** FAT/CD36 is a membrane receptor that facilitates fatty acid transport across the outer mitochondrial membrane. Once inside the outer membrane, FAT/CD36 initiates the process of fatty acid transport into the matrix of the mitochondria.

**Why Each Wrong Option is Incorrect:**

3. **C. Monoacylglycerol lipase (MGL):** MGL hydrolyzes triglycerides into monoglycerides and free fatty acids, which are taken up by cells via various transport proteins. MGL is not involved in fatty acid transport into mitochondria.

4. **D. Mitochondrial inner membrane proteins:** Although mitochondria contain numerous proteins, none specifically transport fatty acids into the matrix. The correct transporters (CPT1 and FAT/CD36) are responsible for fatty acid uptake into mitochondria.

**Core Concept:** Membrane transport proteins like CPT1 and FAT/CD36 play a crucial role in facilitating fatty acid uptake into the mitochondria for β-oxidation, generating ATP, and maintaining cellular energy homeostasis. This process involves the outer mitochondrial membrane, the inner mitochondrial membrane, and the matrix, ensuring efficient fatty acid utilization.