What is the physiological role of carnitine?

What is the physiological role of carnitine?

• A. Catalyzes the breakdown of fats in cytosol.
• B. Synthesize fatty acids in mitochondria.
• C. Acts as a vitamin cofactor for amino acid metabolism.
• D. Transports long-chain fatty acids into the mitochondria for beta-oxidation.

Answer: (D)

Carnitine’s job is to shuttle long-chain fatty acids into the mitochondria so they can be broken down by beta-oxidation to produce energy. Long-chain fatty acids are activated to acyl-CoA in the cytosol, but their entry into the mitochondrial matrix requires the carnitine shuttle. The outer membrane uses CPT I to convert acyl-CoA to acyl-carnitine, which crosses the inner membrane via a translocase. Inside the matrix, CPT II converts it back to acyl-CoA for beta-oxidation. This mechanism is especially important during fasting or prolonged exercise when fats supply a large portion of energy. Short- or medium-chain fatty acids can cross membranes without carnitine, so the shuttle is particularly critical for long-chain fats. Carnitine is not a catalyst of fat breakdown in the cytosol, and fatty acid synthesis occurs in the cytosol rather than in mitochondria, so the shuttle role is not about lipid synthesis or cytosolic lipolysis. It’s also not a vitamin cofactor for amino acid metabolism.

Carnitine’s job is to shuttle long-chain fatty acids into the mitochondria so they can be broken down by beta-oxidation to produce energy. Long-chain fatty acids are activated to acyl-CoA in the cytosol, but their entry into the mitochondrial matrix requires the carnitine shuttle. The outer membrane uses CPT I to convert acyl-CoA to acyl-carnitine, which crosses the inner membrane via a translocase. Inside the matrix, CPT II converts it back to acyl-CoA for beta-oxidation.

This mechanism is especially important during fasting or prolonged exercise when fats supply a large portion of energy. Short- or medium-chain fatty acids can cross membranes without carnitine, so the shuttle is particularly critical for long-chain fats. Carnitine is not a catalyst of fat breakdown in the cytosol, and fatty acid synthesis occurs in the cytosol rather than in mitochondria, so the shuttle role is not about lipid synthesis or cytosolic lipolysis. It’s also not a vitamin cofactor for amino acid metabolism.