Fatty acid transport into mitochondria — name the carrier molecule Which small molecule acts as the dedicated carrier for transporting long chain fatty acyl groups across the inner mitochondrial membrane for beta oxidation?

Introduction / Context:
Long chain fatty acids must enter the mitochondrial matrix to undergo beta oxidation. However, the inner mitochondrial membrane is not freely permeable to acyl-CoA thioesters. Cells therefore use a shuttle system based on a specific carrier molecule.

Given Data / Assumptions:

• Transport targets long chain acyl groups, not free fatty acids alone.
• Movement must occur across the inner mitochondrial membrane.
• Beta oxidation enzymes reside in the mitochondrial matrix.

Concept / Approach:

The carnitine shuttle transfers acyl groups via three coordinated steps: formation of acyl-carnitine by carnitine palmitoyltransferase I on the outer face of the inner membrane, translocation of acyl-carnitine by a carnitine–acylcarnitine translocase, and reconversion to acyl-CoA inside the matrix by carnitine palmitoyltransferase II. Carnitine itself is the small zwitterionic carrier that enables this process.

Step-by-Step Solution:

Verification / Alternative check:

Genetic or pharmacologic disruption of the carnitine shuttle impairs beta oxidation of long chain fatty acids, demonstrating the essential role of carnitine.

Why Other Options Are Wrong:

Acetyl-CoA is a product of beta oxidation, not the shuttle carrier. Dolichol carries sugars in the endoplasmic reticulum. Malonyl-CoA regulates fatty acid oxidation by inhibiting CPT I but is not the carrier. Coenzyme Q transfers electrons in the respiratory chain.

Common Pitfalls:

Confusing regulatory molecules like malonyl-CoA with transport carriers, or assuming acyl-CoA itself crosses the inner membrane unaided.

Final Answer:

Carnitine