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The Role of Microtubules in Cell Division

A cell is a membrane enclosed structure that serves as a body for some organisms, and as a fundamental unit of body tissue for other organisms. While many creatures, such as bacteria, are comprised of one cell, the adult human body is composed of approximately 100 trillion cells. Cell division is the process that facilitates the growth and/or reproduction of all organisms. There are many components and mechanisms involved in cell division, and microtubules play a crucial role.

Cytoplasm
- Cytoplasm is the jelly-like substance that fills the interior of a cell. In organisms that have cells lacking a nucleus (prokaryotes), the cytoplasm represents everything enclosed within the cell's membrane. For organisms that have nucleus containing cells (eukaryotes), the cytoplasm is the material that encircles the nucleus and contains other cell components such as chromosomes.
  
  Cytoplasm is composed of filaments that form a cytoskeleton. The cytoskeleton helps to give the cell structure. The largest type of filament that makes up the cytoskeleton is a microtubule.
Microtubules
- Microtubules are composed of protein units called, tubulin. In addition to being components of cytoplasm, microtubules serve other functions including assisting with a cell's mobility as a material that makes up flagella and cilia. However, it's the microtubule presence in cytoplasm that correlates with microtubule function in cell division.
Cell Division
- Cellular division has three primary purposes. First, cellular division serves as the mode of reproduction for single-celled organisms. This is called mitosis. Secondly, cellular division is the mechanism used by multi-cellular organisms to grow and repair tissues. This second process is also called mitosis. Finally, cellular division is used when sperm and egg (or sexual gametes) are being formed. This is called meiosis.
  
  During cell division, the microtubules within the cytoplasm create a structure called a spindle. The spindle pulls the cell components, chromosomes or chromatids (whichever applies), apart and clusters those components onto opposite ends of the cell.
Spindle Apparatus
- Each time a cell divides, the network of microtubules within the cytoplasm is completely dismantled, and its protein/tubulin units are reassembled to form the spindle. The spindle is also referred to as spindle fibers, mitotic spindle, meiotic spindle, microtubule fibers and the spindle apparatus.
  
  The spindle apparatus also plays a vital role in assigning where the cleavage plane will be situated on the cell. The cleavage plane is the point where the single cell divides to create two cells, called daughter cells. Microtubules complete their formation of the spindle apparatus during a stage of cell division called the metaphase.

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