Bacterial flagellum. Illustration of the attachment point of a bacterial flagellum, used by motile bacteria to propel themselves through their environment. The flagellum consists of a long strand of spiral fibrils of the protein flagellin (green). This strand or filament is rotated like a propeller to achieve motion. It is secured by a hook (centre, grey), with a sleeve and rod structure (lower centre) passing through the outer capsule (orange) and cell wall (red) to the plasma membrane (blue). A set of protein rings (yellow, inner and outer) acts as a motor to drive the rotation of the flagellum. For this artwork with labels, see image C023/8725.