Which statement best describes receptor-mediated endocytosis?

• A. Non-specific uptake of ligands with no receptors
• B. Opens to extracellular space without vesicles
• C. Highly specific, involves receptor proteins, coated pits, and LDLs
• D. Does not require energy

Answer: (C)

Receptor-mediated endocytosis relies on highly specific receptor–ligand interactions. When a ligand binds its receptor on the cell surface, the receptors cluster into clathrin-coated pits and recruit other proteins to help invaginate the membrane. This organized assembly drives vesicle formation, which pinches off and brings the ligand into the cell. Because internalization depends on the receptor, the process is highly selective and can concentrate even small amounts of ligand by packaging them into vesicles for delivery to endosomes and lysosomes. LDL particles are a classic example: they bind LDL receptors, are internalized via these coated pits, and cholesterol is then released inside the cell after endosomal processing.

This is not a non-specific uptake and it does not occur by opening to the extracellular space without vesicles. It also requires energy to drive coat assembly, vesicle scission, and subsequent trafficking, so it’s an active, energy-dependent process.