Question

The amino acid having aromatic R group is :

• A. Leucine
• B. Arginine
• C. Tyrosine
• D. Threonine

Hint:

Remember the three aromatic amino acids: Phenylalanine (Phe), Tyrosine (Tyr), and Tryptophan (Trp). They strongly absorb UV light at 280 nm, which is a common lab technique used to quantify protein concentrations.

Answer 1

The Correct Option is C

Step 1: Concept:
This question tests the structural classification of the 20 standard proteinogenic amino acids, specifically identifying which one contains a stable aromatic ring in its side chain (R group).

Step 2: Step-by-step Explanation:

• Leucine (A): Contains an isobutyl group. It is an aliphatic, non-polar amino acid.

• Arginine (B): Contains a long chain ending in a highly basic guanidino group. It is a positively charged, basic amino acid.

• Threonine (D): Contains a hydroxyl group attached to an aliphatic chain. It is a polar, uncharged amino acid.

• Tyrosine (C): The R group of tyrosine is a phenol group (a benzene ring with a hydroxyl group attached). The benzene ring makes it highly aromatic.

• Note: The three standard aromatic amino acids are Phenylalanine, Tyrosine, and Tryptophan.

Step 3: Final Answer:
Tyrosine is the aromatic amino acid, matching option (C).