ABSTRACT
Mechanistically, exocytosis, endocytosis, and recycling of membranes appear to occur as distinct, albeit overlapping, cellular processes. Each has unique characteristics and fulfills different subcellular functions. The term recycling might well be restricted to processes of rapid return of membrane. These would include rapid transport back to the cell surface of cell surface constituents from inbound material following its endocytosis and the corresponding process of rapid return back to the Golgi apparatus of internal membranes first delivered to the cell surface by exocytosis. Receptor-mediated endocytosis in combination with membrane recycling allows for an efficient delivery of receptor-bound ligands to lysosomes without obligatory loss or degradation of the receptor itself. According to the original lysosome concept, whatever entered the cell was assumed to be degraded although the fate of the entering membranes was unclear. Membrane incorporated by endocytosis moves across the cell and fuses with the opposite cell surface by exocytosis.
