Coated pits are receptors in the cell membrane that participate in the process of receptor mediated endocytosis, in which LDLs are taken up by cells. The pits have a cagelike structure arising from the protein clathrin, which is their primary protein. The receptor recognizes and binds to apoprotein B-100 of the LDL. The entire LDL is engulfed in the process and taken into the cell (See Figure 18.10) to form an endocytic vessicle.