Question

Which from following amino acids has a unique structure so that the side chain connects to the back bone of amino acid at two points ?

• A. Histidine
• B. Proline
• C. Tryptophan
• D. Tyrosine

Hint:

Proline is a cyclic amino acid with a pyrrolidine ring.

Answer 1

The Correct Option is B

Step 1: Think about rings
The side chain forming a ring including the backbone N is the clue.

Step 2: Identify
This ring is the pyrrolidine ring of proline, an imino acid.

Step 3: Contrast
The aromatic rings of tryptophan, tyrosine and histidine are on the end of the side chain, not tied back to the backbone.

Step 4: Answer
Option (B).

Final Answer:
Proline is the cyclic one. This is option (B). \[ \boxed{\text{(B) }\text{Proline}} \]