How many of the following amino acids are essential amino acids?
Glycine, Valine, Serine, Lysine, Tyrosine, Methionine, Proline, Histidine
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 4
Amino acids that cannot be synthesised in the body and must be obtained through diet are essential amino acids. Those the body can make are non-essential. In the table of natural amino acids the essential ones carry an asterisk.
Essential:
Valine
Lysine
Methionine
Histidine
Not essential:
Glycine — non-essential; not marked with an asterisk.
Serine — non-essential; not marked with an asterisk.
Tyrosine — looks like phenylalanine (an essential amino acid) with an extra –OH group, but tyrosine itself is not marked essential.
Proline — non-essential; not marked with an asterisk.
Essential amino acids: valine, lysine, methionine and histidine = 4.
NCERT (2026-27 edition):
10.2.2 Classification of Amino Acids – “…The amino acids, which can be synthesised in the body, are known as non- essential amino acids. On the other hand, those which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids (marked with asterisk in Table 10.2).”
Table 10.2: Natural Amino Acids