Which Step in the Biosynthetic Pathway for Thyroid Hormones Produces $\left(\mathrm{T}_{4}\right)$

Multiple Choice

Which step in the biosynthetic pathway for thyroid hormones produces thyroxine $\left(\mathrm{T}_{4}\right)$ ?

A) Iodide (I-) pump
B) $\mathrm{I}^{-} \rightarrow \mathrm{I}_{2}$
C) $\mathrm{I}_{2}^{+}$ tyrosine
D) Diiodotyrosine (DIT) + DIT
E) DIT + monoiodotyrosine (MIT)