Q64.Hydrophobic effect has a major role in the stabilization of three dimensional structure of proteins. Which of the following amino acids form part of this effect:

A. Glycine, Alanine, leucine
B. Valine, Methionine, Isoleucine
C. Tryptophan, Tyrosine, Phenylalanine
D. Tryptophan, Proline, Phenylalanine
E. Tyrosine, Serine, lysine

Choose the correct answer from the options given below:

(1) A, B, D Only
(2) A, B Only
(3) C, E Only
(4) E, B Only

Hydrophobic amino acids with non-polar aliphatic or aromatic side chains drive the hydrophobic effect by burying in protein cores. The correct answer is option (2): A, B only.

Amino Acid Hydrophobicity Analysis

The hydrophobic effect stabilizes protein 3D structure as non-polar side chains cluster internally, minimizing water contact and maximizing entropy. Glycine (tiny H), Alanine (small CH3), Leucine (isobutyl) in A are hydrophobic (G/A borderline, L strongly so). Valine (isopropyl), Methionine (thioether), Isoleucine (sec-butyl) in B are classically hydrophobic.

Tryptophan (indole), Tyrosine (phenol), Phenylalanine (benzyl) in C mix hydrophobic cores (W/F) with polar OH (Y, hydrogen-bonds water). Tryptophan, Proline (cyclic, non-polar), Phenylalanine in D valid, but Proline disrupts helices—not core hydrophobic driver. Tyrosine, Serine (alcohol), Lysine (charged +) in E mostly hydrophilic.

Option Breakdown

• (1) A, B, D Only: Wrong—D includes helix-breaker Proline, less central to hydrophobic core.

• (2) A, B Only: Correct—pure aliphatic hydrophobics (V,L,I,M,A,G) form stable cores without polar/charged interference.

• (3) C, E Only: Wrong—C partially hydrophobic, E hydrophilic/charged.

• (4) E, B Only: Wrong—E hydrophilic despite B correct.

The hydrophobic effect has a major role in the stabilization of three dimensional structure of proteins by driving non-polar residues inward. Aliphatic amino acids like Leucine, Valine, Isoleucine, and Methionine exemplify this force.

Hydrophobic Amino Acid Groups

• Group A: Glycine (weakest, flexible), Alanine (small methyl), Leucine (branched)—core stabilizers.

• Group B: Valine, Methionine (sulfur adds bulk), Isoleucine—highly non-polar, bury deeply.
  Aromatics (Phe, Trp) contribute but polar Tyrosine/Serine/Lysine solvate externally.

Mechanism in Folding

Water entropy rises when hydrophobics cluster, offsetting H-bonds/salt bridges. Exam focus: aliphatic > aromatic > polar.

Exam Tip

CSIR NET/NEET tests core hydrophobics (A,B). Avoid groups mixing polar residues.​