Substance A is secreted by the liver, travels through the circulatory system bound to a carrier protein, and causes a change in gene expression in its target cell. Substance A is therefore a ligand for ____.
A) a receptor tyrosine kinase
B) a G-protein-coupled receptor
C) a steroid hormone receptor
D) a ligand-gated ion channel
E) guanylyl cyclase

Question

Quizplus · Accepted Answer

Substance A's characteristics match those of a steroid hormone: it is secreted by a gland (the liver), travels in the bloodstream bound to a carrier protein, and alters gene expression in target cells, which implies it acts through a steroid hormone receptor inside the cell.

Substance a Is Secreted by the Liver, Travels Through the Circulatory