Question

Identify which of the following statements about thyroxin is incorrect?
(a) Thyroid gland requires iodine to synthesize thyroxin.
(b) Thyroxin is also called thyroid hormone.
(c) It regulates protein, carbohydrates and fat metabolism in the body.
(d) Iron is essential for the synthesis of thyroxin.

Answer 1

d is wrong

Explanation:

the thyroid gland regulates metabolism by secreting thyroid hormone which has iodine as a major component of it

Answer 2

Answer:

Option D is the incorrect statement about thyroxin.

Explanation:

• Iodine is required for the production of thyroid hormones.
• Iodine is obtained from food sources (Especially iodized salt).
• The circulating iodine is present in ion form i.e., Iodide which has a negative charge.
• Iodide is taken from the bloodstream using Sodium-Iodide Symporter (NIS) into the follicular cell.
• The transport of iodide into the lumen of the cell is carried out by Pendrin (a type of transporter)
• Once the iodide is transported to the lumen, it is oxidized into iodine (I₂) by the hormone thyroid peroxidase present in the lumen
• Thyroid peroxidase then organifies the I₂ by covalently linking it to the tyrosine residues present on the thyroglobulin molecule. This results in the formation of mono-iodotyrosines (MIT) and diiodotyrosines (DIT)(Precursor of thyroid hormone)
• The coupling of two diiodotyrosine (DIT) results in the formation of T4, while the coupling of one monoiodotyrosine (MIT) and one diiodotyrosine results in the formation of T3. These remain attached to the thyroglobulin molecule.
• This processed thyroglobulin is endocytosed back into the follicular cell where it is broken down by the lysosomes and T4 and T3 are separated and then released into the circulating system.

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