There are 5 basic steps of endocytosis:
Endocytosis begins with the recognition of specific molecules or particles in the extracellular microenvironment. Different types of endocytosis involve specific recognition mechanisms.
The plasma membrane folds inwards, and forms a cavity that fills with extracellular fluid, food particles, dissolved molecules, pathogens, and other substances. This invagination can occur through the use of proteins such as clathrin, which coat the membrane and induce its inward bending.
The plasma membrane folds back onto itself until the ends of the in-folded membrane interconnect. This retains the fluid inside by forming a fully enclosed vesicle. In certain cells, long channels also form extending from the membrane deep into the cytoplasm. The vesicle becomes pinched off from the membrane as the ends of the invaginated membrane fuse to one another, forming an intracellular vesicle called an endosome.
The endosome is then transported within the cell depending on the specific cellular context. For example, the endosome can fuse with organelles such as lysosomes or the Golgi apparatus.
Once the molecules are inside the endosome, they are then processed by the cell through different events. These events include recycling, degradation, sorting, or transport to specific intracellular destinations.