Question

Which one of the following acid is hydrophobic with non polar side chain?

• A. Tyrosine
• B. Proline
• C. Glutamine
• D. Serine

Hint:

To identify hydrophobic amino acids, look for side chains made mostly of carbon and hydrogen (aliphatic or aromatic). To identify polar amino acids, look for electronegative atoms like oxygen or nitrogen in groups like -OH (hydroxyl), -CONH\(_2\) (amide), or -SH (thiol). Proline's hydrocarbon ring is a classic nonpolar structure.

Answer 1

The Correct Option is B

Step 1: Concept Overview:
Amino acids are categorized by the properties of their R-groups (side chains). Hydrophobic amino acids possess nonpolar side chains that repel water.
Step 2: Detailed Analysis:
Examining each amino acid's side chain:


Tyrosine: Its side chain features a sizable aromatic ring (hydrophobic) and a polar hydroxyl (-OH) group. The presence of the hydroxyl group classifies tyrosine as a polar amino acid.

Proline: Its side chain, an aliphatic hydrocarbon, cyclizes and binds to the main-chain nitrogen, creating a rigid, nonpolar ring. This nonpolarity designates proline as hydrophobic.

Glutamine: Its side chain includes a highly polar amide group (-CONH\(_2\)). Thus, glutamine is a polar amino acid.

Serine: Its side chain contains a polar hydroxyl (-OH) group, classifying serine as a polar amino acid.

Step 3: Conclusion:
From the provided options, proline uniquely features a completely nonpolar side chain, identifying it as a hydrophobic amino acid.