What are the three types of cell surface appendages of bacteria?

The three types of cell surface appendages of bacteria are flagella, pili, and fimbriae. The overall functions of these appendages are to provide motility and attachment to the bacterial cell. The bacterial flagellum is a whip-like structure that assists in a cell's motility. It is a rigid structure and is made out of a filament, a hook, and a flagellar motor. The filament is a long thin structure that extends from the cell surface and is composed of the protein flagellin. Flagellin proteins become transcribed in the cytoplasm and are transported across the cell wall and membrane. The hook is a coupler that attaches the filament to the motor. The flagellar motor is responsible for assisting in bacterial locomotion as well as chemotaxis. It exists across the cell membrane and cell wall. It has two components, the basal body used for rotation and the stator used for torque. Fimbriae are thin filamentous appendages that extend from the cell and exist in the majority of gram-negative bacteria. They are hair-like structures external to cells that allow the bacteria to bind to the cells they infect. Fimbriae are composed of pilin proteins. Pili are very similar to fimbriae due to the fact that they also extend from the cell and are composed of pilin proteins. They also attach to surfaces and host cells like fimbriae. However, they are usually longer than fimbriae, and only 1-2 are present on each cell. The main thing that separates pili and fimbriae from one another is that pili have additional functions past attachment. Conjugative pili are involved in conjugation, and type IV pili have a role in twitching motility.