Arrange the following amino acids on the basis of increasing side chain size:

(A) Alanine

(B) Glycine

(C) Isoleucine

(D) Leucine

Choose the correct answer from the options given below:

Correct option is C

Explanation of the Correct Option (c): (B), (A), (D), (C)
· Amino acids differ in the size and complexity of their side chains (R-groups).
Increasing order of side chain size:
· Glycine (B)
· Smallest side chain: H (hydrogen)
· Alanine (A)
· Side chain: –CH₃ (methyl group)
· Leucine (D)
· Larger branched alkyl side chain
· Isoleucine (C)
· Bulkier branched side chain than leucine
· Hence, the correct increasing order is: Glycine → Alanine → Leucine → Isoleucine
Explanation of Other Options
Option (a): (A), (B), (C), (D)
· Incorrect because:
· Glycine is the smallest and must come first.
Option (b): (B), (D), (A), (C)
· Incorrect because:
· Alanine should come before leucine.
Option (d): (A), (D), (C), (B)
· Incorrect because:
· Glycine is wrongly placed last.
Key Points
· Glycine → smallest amino acid
· Alanine → simple aliphatic amino acid
· Leucine & Isoleucine → branched-chain amino acids
· Side chain size affects:
· Protein folding
· Steric interactions