Which amino acid is completely oxidized for energy within skeletal muscle?

Which amino acid is completely oxidized for energy within skeletal muscle?

• A. Glycine
• B. Alanine
• C. Leucine
• D. Valine

Answer: (C)

Leucine stands out because it is strictly ketogenic, meaning its carbon skeleton is directed toward energy production rather than glucose formation. When leucine is broken down in skeletal muscle, it is converted into acetyl-CoA and acetoacetate. These products enter energy pathways (the TCA cycle and related routes) and are fully oxidized to generate ATP. They cannot be used to make glucose, which is why leucine is described as being completely oxidized for energy in muscle. In contrast, the other amino acids listed have different fates: valine and isoleucine can yield substrates that feed both energy production and gluconeogenesis, while alanine and glycine are more often linked to glucose production or other metabolic roles rather than serving as the sole energy source in muscle.

Leucine stands out because it is strictly ketogenic, meaning its carbon skeleton is directed toward energy production rather than glucose formation. When leucine is broken down in skeletal muscle, it is converted into acetyl-CoA and acetoacetate. These products enter energy pathways (the TCA cycle and related routes) and are fully oxidized to generate ATP. They cannot be used to make glucose, which is why leucine is described as being completely oxidized for energy in muscle.

In contrast, the other amino acids listed have different fates: valine and isoleucine can yield substrates that feed both energy production and gluconeogenesis, while alanine and glycine are more often linked to glucose production or other metabolic roles rather than serving as the sole energy source in muscle.