Receptor-based endocytosis. Illustration of receptor-mediated endocytosis, where receptors on cells allow them to engulf target molecules (red). The target molecules are first shown outside the cell (centre left). They then bind (upper right) to receptor proteins (orange) on a cell membrane pit coated by the protein clathrin (yellow). The membrane pit forms a vesicle (lower right) around the molecules within the cell cytoplasm (blue). For three forms of endocytosis, see images C023/8787, C023/8789 and C023/8793. For exocytosis (the reverse process), see image C023/8796. For this artwork without labels, see image C023/8795.