Question

Receptors for the protein hormones are located

• A. In the cytoplasm
• B. On the cell surface
• C. In the nucleus
• D. On the endoplasmic reticulum

Answer 1

Answer: (B)

On the cell surface

Proteins cannot cross the plasma membrane, so the receptors of proteinaceous signalling factors must be outside the cell i.e., embedded in the plasma membrane unlike steroid hormones, which is lipid in nature and can easily enter the cell.
For protein hormones, the receptor is membrane associated and embedded in the plasma membrane at the surface of the cell. The interaction of hormone and receptor typically triggers a cascade of secondary effects within the cytoplasm of the cell, often involving phosphorylation or dephosphorylation of various other cytoplasmic proteins, changes in ion channel permeability, or increased concentrations of intracellular molecules, that may act as secondary messengers (e.g., cyclic AMP).