Question

The amino acid considered as a branched-chain amino acid (BCAA) is:

• A. Serine
• B. Leucine
• C. Asparagine
• D. Tyrosine

Hint:

Only three amino acids, Leucine, Isoleucine and Valine, count as branched-chain amino acids.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept.
Branched-chain amino acids (BCAAs) are amino acids whose side chain branches into more than one carbon chain instead of staying a single straight chain.

Step 2: Key Fact.
Only three of the twenty standard amino acids are BCAAs, Leucine, Isoleucine and Valine. All three have a branched aliphatic side chain and are essential amino acids the body cannot make on its own.

Step 3: Detailed Explanation.
Serine has a simple hydroxymethyl side chain, so it is a polar amino acid, not a BCAA. Asparagine carries an amide group on its side chain and is also not branched in the BCAA sense. Tyrosine has an aromatic ring side chain, placing it with the aromatic amino acids. Leucine has a branched isobutyl side chain, which is the defining feature of a BCAA.

Step 4: Final Answer.
Leucine is the branched-chain amino acid among the four choices. \[ \boxed{\text{Leucine}} \]