Molecular model from X-ray diffraction data (PDB ID: 1xi4) of a clathrin cage. Clathrin is a protein that forms a basket or cage-like mesh of proteins on the cell membrane in order to carry cargo into the cell. These coated vesicles transport cargo inside the cell where it is then released. Each subunit of this cage-like lattice is a triskelion formed of three clathrin heavy chains (dark blue) and three clathrin light chains (light blue; short rod structures). This process of internalisation (endocytosis) can be utilised by the cell to take in nutrients and receptors, to sample a cell's local environment, and to turn over membrane components. It also provides a pathway for some pathogens and toxins to enter the cell. Digital artwork 2014.