Microtubules

Microtubules are a component of the cytoskeleton in cells. They are made up of monomers of alpha and beta tubulin which dimerise to form a globular protein by the use of GTP hydrolysis. They are roughly 25 nm in diameter, the largest of all cytoskeletal proteins. Tubulin molecules then polymerize to form void cylinders of microtubules. Taxol stabilises the polymerized form of microtubules by binding to them. It is an important anticancer drug as it affects rapidly dividing cells such as tumour cells

Microtubules have multiple functions within a cell. The rigidity of microtubules allows them to maintain the cell's shape. They also control the movement of the cell as well as the movement of intracellular organelles. Microtubules require organising centres in order to radiate throughout the cell such as centrosomes from which they form asters before growing into mitotic spindles. During mitosis, microtubules form the mitotic spindle required to separate the chromosomes.

Microtubules are also essential for the movement of cilia and flagella, which help with either moving the cell through an environment or moving things (e.g. mucus) past the cell. In unicellular eukaryotes, cilia are mainly used for movement of itself whiles in multicellular organisms groups of cilia usually beat in a wave-like pattern to move the environment past the cell. Flagella usually exhibit an independent bending motion. Despite these differences both cilia and flagella have a similar structure; a basal body with an axoneme; the axoneme has 9 outer doublets of tubules and 2 central singlet microtubules while the basal body is made of 9 sets of 3 microtubules.

Microtubules are polar with a plus and minus end, they can assosiate with motor proteins such as kinesin or dyneins which are used to provide movement of cilium or flagellum in bacteria. Motor proteins hydrolyse ATP to drive movement and their tails can bind vesicles and organelles.