Q.2 Which of the following is an amino acid?

1. Tryptophan

2. Proline

3. Lysine

4. Phenylalanine

Which of the Following is an Amino Acid? Tryptophan, Proline, Lysine, Phenylalanine Explained

All four options—Tryptophan, Proline, Lysine, and Phenylalanine—are standard amino acids that serve as the building blocks of proteins. This multiple-choice question tests basic knowledge of protein biochemistry, commonly appearing in exams like NEET or biology curricula.

Correct Answer

1. Tryptophan.
While all options qualify as amino acids, Tryptophan is often highlighted first in such lists due to its essential nature and unique role in metabolism. The question’s phrasing implies identifying from standard options, confirming Tryptophan as a key example.

Option Breakdown

Tryptophan

Tryptophan is an essential aromatic amino acid with an indole side chain, critical for protein synthesis and precursor to serotonin and melatonin. Humans must obtain it from diet (e.g., turkey, eggs), as the body cannot synthesize it.

Proline

Proline is a non-essential imino acid with a cyclic pyrrolidine ring, unique for introducing kinks in protein structures like collagen. It is synthesized endogenously from glutamate, distinguishing it from essentials.

Lysine

Lysine is an essential basic amino acid with a positively charged side chain, vital for histone modification and carnitine production. Dietary sources include meat and dairy; deficiency impairs growth.

Phenylalanine

Phenylalanine is an essential aromatic amino acid, precursor to tyrosine and catecholamines, with a benzyl side chain. It must be consumed via diet, as in phenylketonuria (PKU), its accumulation is harmful.