Microtubules maintain cell shape, help in cell division, as well as aid in vesicle transport throughout the cell. They provide the cell with a structure, so that the cells do not collapse.
Microtubule structures form many different complicated structures in cells. A single microtubule is a polymer that can bind to others to form spindle fibers. Microtubule doublets form the cilia in specific cell types. Microtubule triplets form the structures of centromeres as well as basal bodies.
Polymerization and depolymerization is driven by GTP binding and hydrolysis on the beta-tubulin monomer. The polymerization and depolymerization events give microtubules a dynamic instability which allows them to find and bind to kinetochores, spindle poles, etc. as well as remain free for subunit exchange.
Microtubules have dynamic instability due to polymerization events as well as a large number of binding sites. This allows microtubules to grow and shrink as well as bind vesicles for transport.
Cohesion is a sticky protein that holds the sister chromatids together in S phase when the chromosomes are duplicated. At the beginning of anaphase, the cohesion is broken down in order for the sister chromatids to be pulled apart.
Condensins help condense the DNA in the chromosomes. They exist in the center of sister chromatids, holding the DNA in a coiled, condensed state. Using ATP hydrolysis, Condensin coils DNA in a test tube.
Cytokinesis (cytoplasmic division) needs to happen after all chromosomes have been properly segregated. If this does not happen, extra chromosomes or missing chromosomes would exist in the daughter cells. This can lead to cell death or disease.
Centrosome duplication occurs in interphase, when the centrioles and other components are duplicated in anticipation for DNA replication. When mitosis starts, the centrosome complex is split in two and each centriole pair becomes part of seperate microtubule organizing centers which nucleates the microtubule structure called an aster. There are two asters that move to opposite sides of the cell and eventually form the two poles of the mitotic spindle that will seperate the sister chromatids.