The Mitotic Spindle
During prophase of mitosis, cytoskeletal microtubules disassemble. As the centriole pairs migrate away from each other, they organize the assembly of a new system of microtubules called the mitotic spindle. Lengthening of these microtubules pushes the centrioles farther and farther apart, ultimately pushing them to opposite poles of the cell.
Then the centrioles cause asters (also composed of microtubules) to radiate outward from the ends of the spindle and anchor it to the plasma membrane. While all this is taking place, some of the spindle fibers attach to protein complexes called kinetochores on the centromere of each pair of sister chromatids. These fibers are referred to as kinetochore microtubules. Those spindle fibers which do not attach to chromosomes are called polar or nonkinetochore microtubules.
The kinetochore tubules pull on the chromosomes until they ultimately line up at the equator of the spindle to form the metaphase plate. During anaphase, the kinetochore fibers shorten, pulling each chromosome towart the end of the cell it faces. The polar microtubules slide past each other (due to the action of kinesin motor proteins), which forces the 2 poles of the cell further apart such that the entire cell elongates.
During telophase, the spindle finally breaks down and disappears.
During prophase of mitosis, cytoskeletal microtubules disassemble. As the centriole pairs migrate away from each other, they organize the assembly of a new system of microtubules called the mitotic spindle. Lengthening of these microtubules pushes the centrioles farther and farther apart, ultimately pushing them to opposite poles of the cell.
Then the centrioles cause asters (also composed of microtubules) to radiate outward from the ends of the spindle and anchor it to the plasma membrane. While all this is taking place, some of the spindle fibers attach to protein complexes called kinetochores on the centromere of each pair of sister chromatids. These fibers are referred to as kinetochore microtubules. Those spindle fibers which do not attach to chromosomes are called polar or nonkinetochore microtubules.
The kinetochore tubules pull on the chromosomes until they ultimately line up at the equator of the spindle to form the metaphase plate. During anaphase, the kinetochore fibers shorten, pulling each chromosome towart the end of the cell it faces. The polar microtubules slide past each other (due to the action of kinesin motor proteins), which forces the 2 poles of the cell further apart such that the entire cell elongates.
During telophase, the spindle finally breaks down and disappears.
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