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: Understanding the Concept:
Amino acids are classified based on the chemical properties of their side chains (R-groups). A hydrophobic amino acid has a nonpolar side chain that is repelled by water.
Step 2: Detailed Explanation:
Let's analyze the side chain of each amino acid:


Tyrosine: The side chain contains a large aromatic ring (hydrophobic part) but also a hydroxyl (-OH) group, which is polar. Due to the hydroxyl group, tyrosine is classified as a polar amino acid.

Proline: The side chain is an aliphatic hydrocarbon group that loops back and bonds to the main-chain nitrogen atom, forming a rigid ring. This side chain is nonpolar and makes proline a hydrophobic amino acid.

Glutamine: The side chain contains an amide group (-CONH\(_2\)), which is highly polar. Glutamine is a polar amino acid.

Serine: The side chain contains a hydroxyl (-OH) group, which is polar. Serine is a polar amino acid.

Step 3: Final Answer:
Among the given options, only proline has a side chain that is entirely nonpolar, making it a hydrophobic amino acid.