Final answer:
The proteins taken up by the cell via receptor-mediated endocytosis are concentrated in coated pits and vesicles coated with clathrin, a protein essential for forming these specialized structures and internalizing selected cargo.
Step-by-step explanation:
Proteins taken up by the cell using specific receptors become concentrated in pits and endocytic vesicles that are coated with clathrin. This protein assists in the formation of specialized structures necessary for the process of receptor-mediated endocytosis. In receptor-mediated endocytosis, clathrin is linked to the membrane via an adaptor protein, which recruits cargo proteins to be internalized.
Coated pits, aided by the protein dynamin, invaginate and pinch off to form clathrin-coated vesicles, bringing extracellular contents into the cell. These vesicles then merge with early endosomes, leading to the separation of the contents from receptors. After delivering their cargo, the vesicles are recycled back to the plasma membrane, disengaging clathrin in the process.