Receptor-gemedieerde endocytose

Receptor-mediated endocytosis is a form of endocytosis where molecules, including metabolites, hormones, and nutrients, are internalized through their specific cell-surface receptors.

Once a molecule binds to its specific receptor on the cell membrane, the membrane bends inwards. Then, clathrin triskelions, structural proteins, bind to adaptor proteins  and polymerize to form a clathrin-coated pit.

Other membrane-bending and fusion proteins are recruited to the neck of the clathrin-coated pit and pinch it off. The coating is rapidly released and the naked vesicle fuses with an early endosome. 

The early endosome has two domains—tubular and vacuolar, with different internal pHs. The low pH of the vacuolar domain causes the endocytosed ligand to be released from its receptor.

While the ligand is retained in the vacuolar domain and is later processed, the associated receptor remains in the tubular domain due to the large surface area to volume ratio of the tubules.  The receptor is then transported back to the cell membrane.