Bacteria contain a wealth of mechanisms that organize their internal and external components into a highly polar structure, frequently with distinctive shape, and constrain certain metabolic functions to particular parts of the cell. For example, cell division generally takes place at the middle of the cell, and a host of interacting proteins are involved in ensuring that the division site is positioned properly. Thus, in spite of the lingering perception among some scientists that these cells are simply bags of freely diffusing enzymes, there is much to be learned from ultrastructural studies. Light microscopy has given evidence of cytoskeletal components that presumably establish and maintain cell shape and participate in cell division.