Phases of mitosisThe process of mitosis is complex and highly regulated. The sequence of events is divided into major phases
KaryokinesisThis is the division of the nucleus known as karyokinesis.
CytokinesisThis is the division of the cytoplasm known as cytokinesis.
Microtubules thus formed are called spindle fibers, and the complete set of the spindle fibers is known as mitotic spindle. During the formation of mitotic spindle, the centrosomes migrate to opposite side of the nucleus.
The nucleolus and the nuclear envelope have degraded, and spindle fibers have invaded the central space. In highly vacuolated plant cells, the nucleus has to migrate into the center of the cell before prophase. The cells of plants lack centrioles. Instead, spindle fibers are formed by the aggregation of tubulin proteins on the surface of the nuclear envelope during prophase.
Metaphase:When the spindle grows to sufficient length, some of the spindle fibers, known as kinetochore fibers, begin searching for kinetochores to attach. When kinetochore fibers attach to kinetochores, the centromeres of the chromosomes arrange themselves along the equator of the cell forming a metaphase plate. A number of other fibers (nonkinetochore) interact with the correspondingfibers from the opposite centrosome.
AnaphaseWhen a kinetochore spindle fibre connects with the kinetochore of the chromosome, it starts to pull toward the originating centrosomes. The pulling force divides the chromosome's sister chromatids, allowing them to separate.
These sister chromatids are now sister chromosomes, and they are pulled apart by shortening of the kinetochore spindle fibres toward the respective centrosomes. Next, the other spindle fibres (without kinetochore) elongate, pushing the centrosomes and the sets of chromosomes apart to opposite ends of the cell. At the end of anaphase, the cell has succeeded in separating identical copies of the genetic material into two distinct groups.
Telophase:Telophase is a reversal of prophase. A new nuclear envelope forms around each set of separated sister chromosomes. Both sets of chromosomes, now surrounded by new nuclear envelopes, unfold back into chromatin. Nuclear division is complete, but cell division has yet one more step to complete.
CleavageCytokinesis is the division of the cytoplasm. In animal cells, cytokinesis occurs by a process known as cleavage. A cleavage furrow develops where the metaphase plate used to be. At the site of the furrow, the cytoplasm has a ring of microfilaments (a part of the cytoskeleton).
The ring contracts deepening the furrow and eventually pinching the parent cell into two.
Cytokinesis in plant cells
|cytokinesis in plant cell|
Cytokinesis in plant cells occurs differently. Vesicles derived from the Golgi apparatus move to the middle of the cell and fuse to form a membrane-bounded disc called the cell plate or phragmoplast.
The plate grows outward and more vesicle fuse with it. Finally, the membranes of the cell plate fuse with the plasma membrane and its contents join the parental cell wall. The result is two daughter cells, each bounded by its own plasma membrane and cell wall .