Cell Biology/Cytoskeleton/Microtubules

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Microtubules in a gel fixated cell

Microtubules as the name suggests is derived from two words- Micro means Small and Tubules means tube like. Microtubules comes under the class of organelles known as Cytoskeleton. Cytoskeletons are the frameworks of the Cell, that form the structural supporting components. Besides these they have other works like Cell movements, muscle contractions and in Cell division. Cytoskeletons are of three types viz, Microtubules, Intermediate filaments and Microfilaments. Microtubules are larger than the other two. Microtubules are composed of tubulin proteins. Tubulin are proteins that form the components of microtubules. The two main types of tubulins are Alpha and Beta tubulins. They form dimers. Microtubules are polymerized and depolymerized according to the cell's physiological status. They are strings radiating from points near the nucleus, called centrosomes. When the cell goes into mitosis (which means it's going to divide), these filaments separate into 2 groups, each one carries an equal number of condensed DNAs to each side of the cell. Therefore, each daughter cell has an equal number of DNAs. The number of DNAs is unique for each species.

Prophase: The two round objects above the nucleus are the centrosomes. The chromatin has condensed.  
Prometaphase: The nuclear membrane has degraded, and microtubules have invaded the nuclear space. These microtubules can attach to kinetochores or they can interact with opposing microtubules.  
Metaphase: The chromosomes have aligned at the metaphase plate.  
Early anaphase: The kinetochore microtubules shorten.  
Telophase: The decondensing chromosomes are surrounded by nuclear membranes. Cytokinesis has already begun; the pinched area is known as the cleavage furrow.