Biochemistry

Thyroxine is a hormone produced by the thyroid gland and is an iodinated derivative of tyrosine, which is an amino acid. The thyroid gland adds iodine to tyrosine to form thyroxine (T4) and triiodothyronine (T3), both of which play essential roles in regulating metabolism.

Explanation:

• Option A: Tyrosine - Correct. Thyroxine is an iodinated derivative of tyrosine, which is the precursor for thyroid hormones.
• Option B: Tryptophan - This is incorrect. Tryptophan is an amino acid, but it is not involved in the production of thyroxine.
• Option C: Threonine - This is incorrect. Threonine is an amino acid, but it is not related to the production of thyroxine.
• Option D: Lysine - This is incorrect. Lysine is an amino acid, but it does not play a role in the production of thyroxine.

Conclusion:

The correct answer is Option A: Tyrosine, as thyroxine is an iodinated derivative of tyrosine.