Most of the energy supplied from protein comes from the metabolism of which type of amino acids?

• A. Aromatic amino acids (phenylalanine, tyrosine, tryptophan)
• B. Sulfur-containing amino acids (methionine, cysteine)
• C. Branched-chain amino acids (leucine, isoleucine, valine)
• D. Basic amino acids (lysine, arginine, histidine)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the context of the question. Proteins are metabolized into amino acids, which can be further broken down to provide energy. Different types of amino acids contribute to energy metabolism in distinct ways.
2. Step 2: Recall the classification of amino acids. Amino acids are categorized based on their side chains, such as aromatic, sulfur-containing, branched-chain, and basic amino acids. Each group has unique metabolic pathways.
3. Step 3: Focus on branched-chain amino acids (BCAAs). These include leucine, isoleucine, and valine. BCAAs are metabolized primarily in muscle tissue rather than the liver, making them a significant source of energy during physical activity or fasting.
4. Step 4: Compare BCAAs to other amino acid groups. Aromatic amino acids (phenylalanine, tyrosine, tryptophan) are involved in neurotransmitter synthesis, sulfur-containing amino acids (methionine, cysteine) are important for redox reactions, and basic amino acids (lysine, arginine, histidine) play roles in protein structure and signaling. These groups are less directly involved in energy metabolism compared to BCAAs.
5. Step 5: Conclude that branched-chain amino acids are the primary contributors to energy metabolism from protein, as their unique metabolic pathway allows them to be directly oxidized for energy in muscle tissue.