Final answer:
AP2 adaptors on clathrin-coated vesicles are responsible for sorting cargo into the vesicle during receptor-mediated endocytosis, guiding internalized substances through the cell's endosomal pathway until they can be processed by lysosomes.
Step-by-step explanation:
AP2 adaptors on clathrin-coated vesicles work by sorting cargo into the vesicle. These adaptors bind to specific membrane proteins that have trapped the desired cargo molecules. Once internalized, these vesicles lose their clathrin and adaptor protein coats, and the vesicles then fuse with early endosomes. The sorting vesicles, or late endosomes, separate the imported content from receptors that are recycled back to the membrane. Eventually, the remaining vesicle becomes a lysosome, where hydrolysis of contents occurs, facilitated by digestive enzymes. This process is integral to receptor-mediated endocytosis, where substances are brought into the cell by initially binding to receptors on the plasma membrane. These receptors congregate in coated pits, which invaginate and pinch off to form the clathrin-coated vesicles, allowing for the internalization of extracellular substances.