Question

Which one of the following amino acids is involved in synthesis of hormone epinephrine in humans?

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

Hint:

Remember the precursors for key neurotransmitters/hormones: \textbf{T}yrosine \(\rightarrow\) \textbf{D}opamine, \textbf{N}orepinephrine, \textbf{E}pinephrine (Adrenaline). \textbf{T}ryptophan \(\rightarrow\) \textbf{S}erotonin.

Answer 1

The Correct Option is C

Step 1: Concept Overview:
Epinephrine, also called adrenaline, is a catecholamine hormone and neurotransmitter derived from an amino acid.
Step 2: Biosynthetic Pathway:
Catecholamine biosynthesis occurs in the following steps:


The initial amino acid is Tyrosine.

Tyrosine is transformed into L-DOPA via tyrosine hydroxylase.

L-DOPA is then converted to Dopamine.

Dopamine converts to Norepinephrine (noradrenaline).

Finally, Norepinephrine is converted to Epinephrine (adrenaline).

Therefore, Tyrosine initiates the pathway. Although Phenylalanine (D) can become Tyrosine via phenylalanine hydroxylase, Tyrosine directly enters catecholamine synthesis. Tryptophan (B) is a precursor for serotonin and melatonin. Threonine is not a precursor for these hormones.
Step 3: Conclusion:
Tyrosine is the direct amino acid precursor in epinephrine synthesis.