A cell membrane-coated pit, also known as a coated pit or clathrin-coated pit, is a specialized area found on the cell membrane of eukaryotic cells. It is involved in a process called endocytosis, which is the internalization of material from the extracellular environment into the cell.
The cell membrane-coated pit is named as such due to its distinctive appearance under electron microscopy, where it exhibits a coated structure. The coat is made up of clathrin, a protein that forms a lattice-like structure around the pit. This clathrin coat is important for the invagination and subsequent formation of a coated vesicle, which is pinched off from the plasma membrane.
The primary role of the cell membrane-coated pit is to facilitate the selective uptake of substances from the extracellular space. It is involved in both receptor-mediated endocytosis, where specific molecules bind to receptors on the cell surface and are subsequently internalized, as well as fluid-phase endocytosis, which involves non-specific engulfment of fluids and solutes.
Once formed, the coated vesicle, with the ingested material inside, moves into the cytoplasm. The clathrin coat is then removed, allowing the vesicle to fuse with other intracellular compartments, such as endosomes or lysosomes. This enables the processing and sorting of the internalized cargo within the cell.
In conclusion, a cell membrane-coated pit is a specialized structure on the cell membrane involved in the process of endocytosis, which allows the cell to selectively internalize specific molecules and fluids from the extracellular environment.
