What best describes receptor-mediated endocytosis?

• A. Endocytosis via pore diffusion
• B. Exocytosis of vesicles to the outside
• C. Binding to receptors triggers vesicle formation for internalization
• D. Ion pair diffusion across the membrane

Answer: (C)

Receptor-mediated endocytosis is the process where a molecule outside the cell binds to a specific receptor on the cell surface, and that binding triggers the membrane to invaginate and form a vesicle that internalizes the receptor–ligand complex. This binding brings receptors together into coated pits, recruits adaptor proteins and clathrin, and then a vesicle buds off and carries the cargo into the cell. It’s a highly selective, energy-dependent mechanism that concentrates and imports larger or scarce ligands, such as cholesterol via the LDL receptor or iron–transferrin complexes.

This differs from diffusion through pores, which would be a non-specific, passive movement; exocytosis, which exports material out of the cell; and simple ion-pair diffusion, which isn’t a vesicle-mediated uptake mechanism. The key feature here is that receptor binding directly triggers vesicle formation for internalization.