Structural Biochemistry/Mitotic Spindles
Mitotic spindles are filaments of microtubule that move the chromosomes towards opposite poles during metaphase of mitosis. Mitotic spindles compose of actin and myosin filaments. Cables of actin stretch from pole to pole of the mitotic spindle and myosin control spindle length and shape. Mitotic spindles are attached to a centrosome, the site of microtubule organization and anchor of the spindles. Metaphase plate forms when the chromosomes are aligned in the center of the cell with the mitotic spindles attached to the kinetochores, site of microtubule-chromosome attachment, of chromosomes. Mitotic spindles play a key role in acting as the "fishing line" to move the chromosomes to opposite poles during cell division. In addition, centrosomes are the "reel" that draws the spindle fibers closer to the poles. Disruption of the mitotic spindle formation or arrangement can have huge consequences such as leaving one cell with too many or too little chromosomes.
The mitotic spindle is known as a director that moves chromosomes during mitosis. It is currently unknown how the microtubule fibers move the chromosomes, although it is believed that motor proteins act like carriers moving the chromosomes in different directions. Others tend to believe that the fibers grow and shrink and in doing so move the chromosomes back and forth. Issues arise when the spindle makes mistakes. Sometimes the meiotic spindle doesn’t separate correctly and therefore an abnormal amount of chromosomes are present which could cause Down syndrome.
Machalek M Alisa. http://publications.nigms.nih.gov/insidethecell/insidethecell.pdf "Inside the Cell" The National Institute of General Medical Sciences (2010): 36-37.