Final answer:
AP2 adaptors in the clathrin coat connect the cytoplasmic tails of specific membrane receptors and clathrin molecules during receptor-mediated endocytosis, which is a key part of how substances are internalized by cells. The correct option is (2)
Step-by-step explanation:
The AP2 adaptors of the clathrin coat are responsible for connecting the cytoplasmic tails of specific membrane receptors and clathrin molecules during the process of receptor-mediated endocytosis. Receptor-mediated endocytosis is a cellular process that uses clathrin-coated pits to internalize extracellular substances that have been bound to their respective membrane receptors. Initially, the substance to be internalized will bind to its specific membrane receptor. Subsequently, these receptors cluster in regions of the cell membrane known as coated pits. As AP2 adaptors link the receptors to clathrin, the coated pits invaginate, eventually pinching off to form a clathrin-coated vesicle which is brought into the cell.
The correct answer to the student's question is therefore option 2: AP2 adaptors connect the cytoplasmic tails of specific membrane receptors and clathrin molecules. This facilitates the gathering of the receptors in the coated pits and the subsequent internalization of the receptors and their bound ligands as clathrin-coated vesicles. The vesicles then deliver their contents to their destinations within the cell, and the clathrin and associated adaptor proteins are recycled.