One essential component of each eukaryotic cell is the cytoskeleton. Microtubules, tiny tubes consisting of a protein called tubulin, are part of this skeleton of cells. Cilia and flagella, which are antenna-like structures that protrude from most of the cells in our body, contain many microtubules. An example of flagell is the sperm tail, which is essential for male fertility and thus for sexual reproduction. The flagellum has to beat in a very precise and coordinated manner to allow progressive swimming of the sperm. Failure to do so can lead to male infertility.