Activated fatty acid is transported to mitochondria from cytosol by

The correct option is Carnitine.

To understand why this is the correct answer, let's break down the transport of fatty acids into the mitochondria step-by-step:

1. Activation of Fatty Acids:
Before fatty acids can be metabolized for energy through β-oxidation, they must first be activated in the cytosol. This process is catalyzed by the enzyme acyl-CoA synthetase, which attaches a Coenzyme A (CoA) group to the fatty acid, forming an acyl-CoA (activated fatty acid). This step consumes energy in the form of ATP.

2. The Mitochondrial Membrane Barrier:
The activated fatty acyl-CoA is located in the cytosol. While the outer mitochondrial membrane is relatively permeable, the inner mitochondrial membrane is completely impermeable to Coenzyme A and its derivatives (such as acyl-CoA). Therefore, the activated fatty acid cannot directly cross into the mitochondrial matrix where the enzymes for β-oxidation are located.

3. The Carnitine Shuttle:
To bypass this barrier, cells utilize a specialized transport mechanism known as the carnitine shuttle:
• Step A: At the outer mitochondrial membrane, the enzyme carnitine palmitoyltransferase I (CPT-I) transfers the fatty acyl group from CoA to a molecule called carnitine, forming acylcarnitine.
• Step B: A transport protein called carnitine-acylcarnitine translocase, located in the inner mitochondrial membrane, assists in shuttling the acylcarnitine across the membrane into the matrix in exchange for a free carnitine molecule moving out.
• Step C: Once inside the matrix, the enzyme carnitine palmitoyltransferase II (CPT-II) transfers the fatty acyl group back to an intramitochondrial CoA molecule, regenerating fatty acyl-CoA ready for β-oxidation. The free carnitine is recycled back to the intermembrane space.

Conclusion:
Thus, carnitine is the essential carrier molecule responsible for transporting activated fatty acids across the inner mitochondrial membrane from the cytosol into the mitochondrial matrix.