Substance E is made in the pancreas, travels through the blood, and binds to a surface receptor on a target cell. After dimerization and autophosphorylation, the receptor activates a signaling protein. Substance E is therefore the ligand for ____.
A) a receptor tyrosine kinase
B) a G-protein-coupled receptor
C) a hormone receptor
D) a ligand-gated ion channel
E) guanylyl cyclase

Question

Quizplus · Accepted Answer

The description of substance E's mechanism of action—binding to a surface receptor, causing dimerization and autophosphorylation, and then activating a signaling protein—matches the characteristics of a receptor tyrosine kinase (RTK). RTKs are known for their role in the phosphorylation of tyrosine residues on themselves (autophosphorylation) and other proteins, which is a key step in transmitting signals from the extracellular ligand (substance E) to the cell's interior.

Substance E Is Made in the Pancreas, Travels Through the Blood