Thyroxine `(T_(4))` or tetraiodothyronine and Triiodothyronine `(T_(3))` , produced by the thyroid gland, are synthesised from

Options

A. Phenylalanine
B. Cholesterol
C. Tyrosine
D. Glycoprotein

Answer

**Step-by-Step Solution:**

1. **Identify the Source**: Thyroxine (T4) and Triiodothyronine (T3) are hormones produced by the thyroid gland.

2. **Understand the Composition**: Both T4 and T3 are synthesized from the amino acid tyrosine, which is derived from dietary proteins.

3. **Role of Iodine**: Iodine is an essential element required for the synthesis of these hormones. The thyroid gland absorbs iodine from the bloodstream.

4. **Synthesis Process**: The synthesis of T4 and T3 involves the following steps:
- The thyroid gland combines tyrosine with iodine.
- The enzyme thyroperoxidase catalyzes the iodination of tyrosine residues in thyroglobulin, a protein stored in the thyroid gland.
- This process leads to the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT).
- MIT and DIT are then coupled to form T3 and T4. Specifically, one MIT and one DIT combine to form T3, while two DIT molecules combine to form T4.

5. **Release into the Bloodstream**: Once synthesized, T3 and T4 are stored in the thyroid gland until they are needed. When required, they are released into the bloodstream to regulate metabolism and other physiological functions.

**Final Answer**: Thyroxine (T4) and Triiodothyronine (T3) are synthesized from the amino acid tyrosine and iodine in the thyroid gland.

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