Which of the following is not an essential amino acid?

Alanine

The correct answer is Option (4) → Alanine

Essential amino acids are those which our body cannot synthesize and therefore must be obtained from food.

1. Histidine Histidine is considered an essential amino acid, especially important for infants and growing children. The body cannot synthesize enough of it, so it must be obtained from the diet.

2. Phenylalanine Phenylalanine is an essential amino acid. It is required for protein synthesis and is a precursor for important molecules like tyrosine, dopamine, and adrenaline.

3. Lysine Lysine is also an essential amino acid. Humans cannot synthesize it, and it plays key roles in protein formation, calcium absorption, and hormone production.

4. Alanine Alanine is a non-essential amino acid because the human body can synthesize it from pyruvate during normal metabolism.