Endocytosis - pinocytosis, receptor mediated and Transcytosis

Pinocytosis is the process in which a cell "drinks" a tiny droplet Of extracellular fluid, including its solutes. Pinocytosis (Cell Drinking) is the process by which the cell takes in fluids (as well as any small molecules dissolved in those fluids). • The plasma membrane folds inward to form the vesicle, which then pinches Off and moves into the cytosol. • Like phagocytosis, vesicles fuse with lysosomes and the solutes are digested. • Receptor-mediated endocytosis imports needed materials like certain hormones, antibodies, vitamins, and low-density lipoproteins into a cell. • Specific receptor proteins bind with these substances and interact with clathrin proteins in an area of the membrane called clathrin- coated pit causing the formation of a vesicle. • Inside the cytosol the vesicle sheds the clathrin which is recycled back to the membrane. • The uncoated vesicle fuses with an endosome and the transported substance and receptor are separated and sorted. • One carrier vesicles returns many of the receptors to the membrane. • A different carrier vesicle transports the ingested substance, and some receptors, to a late endosome, which binds to a lysosome where the substances are digested for use. • In certain cells, receptor- mediated endocytosis transports substances across the cell for release into the extracellular fluid on the other side. This process is called transcytosis.

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