When these receptors encounter a molecule of transferrin, they bind tightly to it. The complex of transferrin and its receptor is then engulfed by endocytosis. Ultimately, the iron is released into the cytosol . Receptor-mediated endocytosis is many thousand times more efficient that simple pinocytosis is enabling the cell to acquire the macromolecules it needs. Receptor Cells take up cholesterol by receptor-mediated endocytosis.
Cholesterol is an essential component of all cell membranes.
Cholesterol is a hydrophobic molecule and quite insoluble in water. Instead it is carried in tiny droplets of lipoprotein. The most abundant cholesterol carriers in humans are the low-density lipoproteins or LDL s. Over a thousand molecules of cholesterol are bound to the hydrophobic interior of LDL particles. The first step in acquiring LDL particles is for them to bind to LDL receptors exposed at the cell surface.