Which of the following is an essential amino acid that must be obtained through the human diet because the body cannot synthesize it?
Answer and explanation
Correct answer: B. Tryptophan
- Step 1: Amino acids are divided into essential (must be ingested) and non-essential (synthesized endogenously from metabolic intermediates).
- Step 2: The ten standard essential amino acids are valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, threonine, histidine, lysine, and arginine.
- Step 3: Tryptophan is an aromatic essential amino acid serving as the biosynthetic precursor for serotonin, melatonin, and niacin.
Answer
Tryptophan.
Why not the others: Alanine is non-essential and synthesized from pyruvate via transamination; Glutamic acid is non-essential and synthesized from -ketoglutarate; Glycine is non-essential and synthesized from serine.
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