Question

Which of the following are synthesized by tyrosine?
A. Thyroid hormone
B. Epinephrine
C. Melanin
D. Haem
Choose the correct answer from the option given below:

• A. A, D
• B. B, D
• C. B, C
• D. A, B, C

Hint:

Tyrosine Biosynthetic Products: Catecholamines (Dopamine, Epinephrine, Norepinephrine), Thyroid Hormones ($T_3, T_4$), and Melanin. Heme is from Glycine.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
L-Tyrosine is a versatile aromatic biosynthetic precursor for catecholamines, thyroid hormones, and melanin pigments.
Key Formula or Approach:
\[ \text{Tyrosine} \longrightarrow \begin{cases} \text{Thyroglobulin Iodination} \longrightarrow \text{Thyroid Hormones } (T_3, T_4) \text{DOPA} \longrightarrow \text{Dopamine} \rightarrow \text{Norepinephrine} \rightarrow \text{Epinephrine} \text{DOPA} \xrightarrow{\text{Tyrosinase}} \text{Dopaquinone} \longrightarrow \text{Melanin Pigments} \end{cases} \]

Step 2: Detailed Explanation:
Biosynthetic pathways originating from L-Tyrosine:
1. A. Thyroid Hormones ($T_3, T_4$): Synthesized by iodination and coupling of tyrosine residues in thyroglobulin.
2. B. Epinephrine (Adrenaline): Synthesized from tyrosine via the catecholamine pathway: $\text{Tyrosine} \rightarrow \text{L-DOPA} \rightarrow \text{Dopamine} \rightarrow \text{Norepinephrine} \rightarrow \text{Epinephrine}$.
3. C. Melanin: Synthesized from tyrosine via tyrosinase in melanocytes.
4. D. Haem: Synthesized from Glycine + Succinyl-CoA (via $\delta$-aminolevulinic acid), not tyrosine.
Thus, A, B, and C are synthesized from tyrosine.

Step 3: Final Answer:
Hence, the compounds synthesized by tyrosine are A, B, C, corresponding to option (D).