Question

Which one of the following amino acids is amphipathic in nature?

• A. Lysine
• B. Aspartic acid
• C. Arginine
• D. Tyrosine

Hint:

Aromatic amino acids like Tyrosine and Tryptophan contain large non-polar rings with polar substituents (\(-OH\) or indole \(-NH\)).
This dual character makes them classic amphipathic amino acids.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Amphipathic (or amphiphilic) molecules contain both hydrophilic (polar, water-soluble) and hydrophobic (non-polar, lipid-soluble) regions.

Step 2: Detailed Explanation:
Amino acids are classified based on the chemical nature of their side chains (R-groups):
- Lysine (A) and Arginine (C): Have highly basic, positively charged side chains, making them strongly hydrophilic.
- Aspartic acid (B): Has a carboxylate side chain that is negatively charged and highly hydrophilic at physiological pH.
- Tyrosine (D): Possesses an aromatic benzene ring (hydrophobic, lipophilic) attached to a polar hydroxyl (\(-OH\)) group (hydrophilic, polar). This distinct separation of polar and non-polar regions within its side chain makes tyrosine amphipathic. It is often found at lipid-water interfaces in membrane proteins.

Step 3: Final Answer:
The amphipathic amino acid is Tyrosine, corresponding to option (D).