Match List-I (amino acid) with List-II (Characteristic Side Chain)

Choose the correct answer from the options given below:

(A)-(II), (B)-(I), (C)-(IV), (D)-(III)

The correct answer is Option (1) → (A)-(II), (B)-(I), (C)-(IV), (D)-(III)

Amino acids differ in the R-group (side chain) attached to the a-carbon. Identification of amino acids is often based on their characteristic side chains:

• Aromatic ring → Phenylalanine
• Branched alkyl chain → Leucine / Isoleucine
• Long chain ending in $-NH_2$ → Lysine

Matching Explanation

(A) Phenylalanine → (II) $C_6H_5CH_2-$

Phenylalanine contains a benzyl group (phenyl ring + $CH_2$). This aromatic side chain makes it nonpolar and hydrophobic. So it matches with the phenyl-containing group.

(B) Leucine → (I) $(CH_3)_2CHCH_2-$

Leucine has an isobutyl side chain. It is a branched-chain, hydrophobic amino acid. The structure matches $(CH_3)_2CHCH_2-$.

(C) Lysine → (IV) $H_2N-(CH_2)_4-$

Lysine contains a long aliphatic chain ending in an amino group. This makes lysine a basic amino acid. Hence, it corresponds to $H_2N-(CH_2)_4-$.

(D) Isoleucine → (III) $CH_3-CH_2-CH(CH_3)-$

Isoleucine has a sec-butyl side chain. It is also branched but differs from leucine in branching  position. This matches $CH_3-CH_2-CH(CH_3)-$.