Question

Which one of the following is NOT an essential amino acid?

• A. Threonine
• B. Tryptophan
• C. Tyrosine
• D. Valine

Hint:

Tyrosine is synthesized from phenylalanine in the body, so it is considered non-essential under normal physiological conditions.

Answer 1

The Correct Option is C

Step 1: Understand essential amino acids.
Essential amino acids are those amino acids that cannot be synthesized sufficiently by the human body and therefore must be obtained from the diet.

Step 2: Analyze threonine.
Threonine is an essential amino acid because humans cannot synthesize it internally. Hence, it must be supplied through food. Therefore, option (A) is an essential amino acid.

Step 3: Analyze tryptophan.
Tryptophan is also an essential amino acid and serves as a precursor for serotonin and niacin synthesis. Thus, option (B) is essential.

Step 4: Analyze tyrosine.
Tyrosine is generally classified as a non-essential or conditionally essential amino acid because it can be synthesized in the body from phenylalanine. Hence, it is not strictly essential under normal conditions.

Step 5: Analyze valine.
Valine is one of the branched-chain amino acids and is essential for humans because it cannot be synthesized by the body. Therefore, option (D) is essential.

Step 6: Compare all the options.
Among the given amino acids, threonine, tryptophan, and valine are essential amino acids, whereas tyrosine is synthesized from phenylalanine.

Step 7: Final conclusion.
Therefore, tyrosine is NOT an essential amino acid.
\[ \boxed{\text{Tyrosine}} \]
Hence, the correct answer is option (C).