Receptor-mediated endocytosis is characterized by?

• A. Highly selective uptake via receptor binding
• B. Non-selective engulfment of extracellular material
• C. Direct fusion with lysosomes
• D. Exocytosis

Answer: (A)

Selective uptake through receptor binding is the hallmark of receptor-mediated endocytosis. Specific ligands bind to their corresponding receptors on the cell surface, and this receptor–ligand interaction triggers the inward budding of vesicles (often via clathrin-coated pits) that internalize the complex. Because uptake depends on the presence of the right receptor, this process is highly selective and efficient for concentrating particular molecules, such as transferrin-bound iron or LDL cholesterol. After internalization, the vesicle traffic leads to early endosomes, where the acidic environment can cause ligand–receptor dissociation, receptors are recycled to the membrane, and ligands are delivered to lysosomes or other destinations for processing.

Non-selective engulfment describes a more general, non-specific uptake (pinocytosis) and lacks this receptor-driven specificity. Direct fusion with lysosomes is not how uptake starts—the vesicles form first and then fuse with endosomes/lysosomes later. Exocytosis is the opposite process, releasing material from the cell rather than taking it in.