16. Which one of the following small molecules is a prerequisite for fatty acid oxidation?
(A) Inositol
(B) Choline
(C) Carnitine
(D) Glycerol

Carnitine is the prerequisite small molecule for fatty acid oxidation. It enables the transport of long-chain fatty acids into mitochondria for beta-oxidation.

Correct Answer

The correct option is (C) Carnitine. Carnitine acts as a carrier in the carnitine shuttle system, transferring activated long-chain fatty acids (acyl-CoA) across the inner mitochondrial membrane for beta-oxidation, the primary pathway for fatty acid breakdown to generate energy. Without carnitine, long-chain fatty acids cannot enter the mitochondrial matrix, halting oxidation.

Role of Carnitine

Carnitine facilitates fatty acid transport via enzymes like carnitine palmitoyltransferase I (CPT-I) and II (CPT-II). Acyl-CoA binds carnitine outside the mitochondria, forming acylcarnitine, which crosses the membrane and regenerates acyl-CoA inside for beta-oxidation. This process is vital during fasting or exercise when fatty acids serve as the main energy source.

Why Not the Others?

• (A) Inositol: Functions as a structural component in cell membrane phospholipids and a signaling molecule precursor, but plays no direct role in fatty acid transport or oxidation.

• (B) Choline: Precursor to acetylcholine and phosphatidylcholine (a lipid), aiding membrane integrity and lipoprotein assembly, unrelated to mitochondrial fatty acid entry.

• (D) Glycerol: Backbone of triglycerides and phospholipids; released during lipolysis but not involved in transporting fatty acids for oxidation.

Biochemistry Context

Fatty acid oxidation (beta-oxidation) occurs in mitochondria, requiring prior activation to acyl-CoA in the cytosol. Short- and medium-chain fatty acids diffuse freely, but long-chain ones depend on carnitine, making it indispensable for efficient energy production from lipids. Carnitine deficiency impairs this process, linking to metabolic disorders.