Prophase: early in prophase the chromosomes condense and become visible under special stain.

The nuclear membrane breaks down and the spindle apparatus begins to form.

Spindle formation in prophase is largely controlled by the mitotic centres that define the poles.

The assembly of the microtubules that form the spindle are organized by special regions known as Microtubule organizing centres MOC

The mitotic centres of animal cells are usually associated with centrioles and for a long time it was assumed that these structures were the organizing centres for spindle assembly. However, many species including all higher plants complete the formation of the spindles without the presence of centrioles.

There are two types of microtubules in the spindle or centromeric cpindle fibres:

1) The kinetochore microtubules that attach the centromere (through the kinetochore) to the poles and

2) the polar microtubules that connect pole to pole (but do not attach to any chromosomes0 or continuous spindle fibers.

Metaphase:

By the on set of metaphase the chromosomes have lined up along the equatorial plane. At this point the centromeres of the chromosomes split and the resulting daughter chromosomes are pulled apart.

Anaphase:

Is the movement of the daughter chromosomes towards opposite poles. the movement is generated by the spindle apparatus. Two distinct processes appear to be involved in movement of the daughter chromosomes they are:

1) The spindle lengthens as the continuous spindle fibers slide past another. This motion pushes the poles apart and may begin the movement of the daughter chromosomes apart and

2) the other mechanism for chromosome movement is due to subunit disassembly of the centromeric spindle fibers at the microtubular organizing center this shortens the centromeric spindles and reels in the chromosomes.

Telophase:

Is in effect prophase in reverse. it can be seen to be beginning when the chromosomes have moved to their respective poles and they begin to uncoil, the spindle disassembles, nuclear membranes form around each new set of chromosomes and the nucleoli reappear. Also at this time, in animal cells the centrioles replicate, i.e. they create copies of themselves so now 2 sets (pairs) exist in each daughter cell. As well this is the time of cytokinesis or division of the cytoplasm.

in animals cytokineis begins with a furrow along the cells equator. This furrow eventually becomes a deep grove called the cleavage furrow. By the time the cleavage furrow has pinched all the way through two new daughter cells have been formed.

This process of mitosis as described above is essentially the same in plants which adds to the universal nature of life on earth. the only major difference is the absence of centrioles in plants and the lack of an Aster.

Cytokensis, as well, proceeds in plants by a different mechanism. Plant cells simply generate a new cell wall between the developing telophase nuclei.

This is accomplished by a cell plate formation. The cell plate originates from the fusion of several (many) vesicles which originate from the golgi. The cell plat fills with pectin and forms the middle lamella. Plasma membrane is laid down on the surface of the cell 0plat and a new primary cell wall (cellulose) is secreted through the cell membrane and each side of the cell plate.