Final answer:
In the thyroid gland, a peroxidase enzyme attaches iodine to the tyrosine amino acid to make thyroxine (T4), a thyroid hormone.
Step-by-step explanation:
In the thyroid gland, a peroxidase enzyme attaches iodine to the tyrosine amino acid found in thyroglobulin to make thyroxine (T4), a thyroid hormone. T4 has four iodine ions attached to tyrosine. This process of attaching iodine to tyrosine forms the basis of thyroid hormone synthesis.