Which of the following compounds is an example of an essential amino acid that cannot be synthesized endogenously by the human body and must be acquired through food?
Answer and explanation
Correct answer: A. L-Lysine
- Step 1: Humans require 20 standard proteinogenic amino acids, 10 of which can be synthesized in the human body from metabolic intermediates (non-essential amino acids).
- Step 2: The other 10 amino acids cannot be synthesized by human metabolic pathways and are classified as essential amino acids (valine, leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine, arginine).
- Step 3: Among the choices, L-Lysine is an essential amino acid.
Answer
L-Lysine.
Why not the others: L-Glycine is synthesized from serine and choline; L-Alanine is synthesized by transamination of pyruvate; L-Serine is synthesized from 3-phosphoglycerate.
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