Question

Thyroid hormone receptor (TR) regulates growth, development, and differentiation of mammals. TR contains both a domain that binds to T3, the thyroid hormone, and a separate domain that binds to DNA. Which of the following BEST explains how TR signals?

A. T3 binds to TR at the cell membrane, which then releases second messengers to regulate gene expression.
B. T3 binds to DNA at the cell membrane, which then releases second messengers to regulate gene expression.
C. T3 diffuses through the cell membrane to bind to TR, which then binds to DNA to regulate gene expression.
D. T3 diffuses through the cell membrane to bind to DNA, which then binds to TR to regulate gene expression.

Answer 1

C. T3 diffuses across the cell membrane, attaches to Tr, and then binds to DNA to control gene expression.

Explanation: Thyroid hormone, as a ligand, diffuses across the plasma membrane, then searches for the nucleus TR (Thyroid receptor and RxR aie heterochimeric bind to DNA).

When Thyroid Hormone binds to the A domain of T3, Corepressor Proteins are removed, which stimulates gene transcription.