1. Cell membrane invagination: The cell membrane begins to invaginate or fold inward, enclosing the large molecule or particle to be taken up by the cell. This invagination is driven by the polymerization of actin filaments on the cytoplasmic face of the membrane.
2. Formation of endocytic vesicle: As the cell membrane invagination deepens, it forms a pocket-like structure called an endocytic vesicle, which remains connected to the cell membrane by a narrow neck. The large molecule or particle becomes enclosed within the endocytic vesicle.
3. Membrane fission and separation: Once the endocytic vesicle is fully formed, the narrow neck connecting it to the cell membrane undergoes fission. The endocytic vesicle is then separated from the plasma membrane and moves deeper into the cytoplasm of the cell.
4. Fate of the endocytic vesicle: The endocytic vesicle containing the internalized molecule may undergo different fates depending on the type of molecule and the cell type. Some vesicles may fuse with early endosomes, which then mature into late endosomes and eventually lysosomes. Inside lysosomes, the internalized molecule is subjected to degradation by hydrolytic enzymes. Alternatively, some endocytic vesicles may also be recycled back to the cell membrane through a process called exocytosis.
In summary, the portion of cell membrane that surrounds a large molecule during endocytosis is internalized into the cell as an endocytic vesicle. The subsequent fate of the endocytic vesicle and its contents depends on various cellular mechanisms, involving potential transport, degradation, or recycling of the internalized molecule.
