Where do amino acids travel after absorption to support protein synthesis?

• A. Liver, heart, brain
• B. Muscle, heart, bone, and brain
• C. Bone and marrow only
• D. Muscle, heart, bone, and brain

Answer: (D)

After absorption, amino acids are carried in the bloodstream to tissues that are actively building proteins. Muscles, heart, bone, and brain all synthesize new proteins to support growth, repair, and function, so amino acids delivered in the blood are used by these tissues for protein synthesis. While the liver initially handles many amino acids via portal circulation, the question highlights the tissues where amino acids travel to support ongoing protein production beyond the liver, namely muscle, heart, bone, and brain. In short, circulating amino acids are available to multiple tissues that continually synthesize proteins, with these four being key examples.