(A) P-1, Q-6, R-5, S-4

(B) P-5, Q-7, R-4, S-8

(C) P-2, Q-5, R-3, S-4

(D) P-3, Q-1, R-2, S-6

Correct Answer

✅ Option (D): P-3, Q-1, R-2, S-6

Detailed Explanation

Tyrosine undergoes multiple chemical modifications in biological systems, each leading to a specific product or functional role.

P) Tyrosine hydroxylation → DOPA (3)

• Hydroxylation of tyrosine produces DOPA (dihydroxyphenylalanine).

• This reaction is catalyzed by tyrosine hydroxylase.

• DOPA is a precursor for catecholamines.

✔ Correct match: P–3

Q) Tyrosine iodination → Thyroxine (1)

• Iodination of tyrosine residues occurs in the thyroid gland.

• This process forms thyroxine (T₄) and triiodothyronine (T₃).

• Iodine is covalently added to tyrosine residues in thyroglobulin.

✔ Correct match: Q–1

R) Tyrosine phosphorylation → T cell receptor (2)

• Tyrosine phosphorylation is a key mechanism in signal transduction.

• T cell receptors and many signaling proteins depend on phosphorylation of tyrosine residues.

• This modification is catalyzed by tyrosine kinases.

✔ Correct match: R–2

S) Tyrosine oxidation → Melanin (6)

• Oxidation of tyrosine leads to the synthesis of melanin.

• This process is catalyzed by the enzyme tyrosinase.

• Melanin is responsible for pigmentation of skin, hair, and eyes.

✔ Correct match: S–6

Why Option (D) Is Correct

Only Option (D) correctly matches all four tyrosine modifications with their true biological products or roles.

Why Other Options Are Incorrect

• Option (A): Incorrect association of phosphorylation and oxidation.

• Option (B): Endorphin and serotonin are not direct products of tyrosine modification.

• Option (C): Estradiol receptor and epinephrine are wrongly matched.

Quick Memory Trick

• Hydroxylation → DOPA

• Iodination → Thyroxine

• Phosphorylation → Signal receptors

• Oxidation → Melanin

Exam Relevance

🔹 Frequently asked in CSIR-NET Life Sciences
🔹 Important for biochemistry & metabolism units
🔹 High-yield concept for match-the-following questions