cell division

Cell division:

The cell life cycle has two major parts, being interphase and mitotic phase, or cell division. Although the term "interphase" leads one to believe that it is not but a resting period, this is not true. During interphase, which is the longer of the two, the cell is quite active, resting only from division. A more accurate term would be metabolic phase

The purpose of mitosis is to produce more cells for growth and repair purposes. It is essential that the resulting cells both have the same genetic material, the deoxyribonucleic acid (dna) is duplicated near the end of interphase. DNA is made up of nucleotides arranged in a double helix. Each helix is bonded to the other via hydrogen bonds between the nitrogen bases of the nucleotides. An enzyme untwists the helixes, and splits them apart. Each half is a template for re-building the other side. Adenine to thymine, guanine to cytosine. The fist part of cell division is mitosis, the division of the nucleus and it's contents. The second is cytokenesis, the division of the cytoplasm, which takes place near the ending of mitosis. Mitosis itself is made up of four stages:

Prophase it the first stage, in which the chromatin threads coil and shorten int visible, bar-like structured named chromosomes. Since dna replication has occurred in interphase, each chromosome is actually of two strands, each known as a chromatid, and held together by a body called a centromere. The centrioles begin to migrate to opposing ends of the nucleus, and directing the construction of mitotic spindles between them. These spindles form structures which will be used to pull the chromosomes apart. By the end of prophase, the nuclear membrane and the nucleoli have broken down and disappeared, and the chromosomes have become attached to the spindle fibers at the centromere
In metaphase, the chromosomes cluster and become aligned at the center of the spindle fibers, forming a straight line of chromosomes that can been seen
During anaphase, the centromeres split, and release the two chromatids- now called chromosomes again- to be pulled by their half-centromeres towards opposite centriols
Anaphase is finished when the chromosome movement has ended Telophase is the last phase of mitosis. The chromosomes at each end of the cell uncoil, and become the thread-like chromatin once more. The spindle fibers break down, and a nuclear membrane forms about each chromatin mass. The nucleoli appear in each of the daughter cell nuclei

Cytokenesis begins during late anaphase and ends during telophase. A cleavage furrow appears over the midline of the cell, and squeezes or pinches the original cytoplasmic mass into two parts. Each resulting daughter cell is slightly smaller than the original, but is genetically identical to it. The cells grow and carry out normal cellular activities until it's time comes to divide.

Although nucleus and cytoplasmic division usually go together, in some case, such as liver cells, cells become binucleate or multinucleate cells. When mitosis "goes wild", the result is cancer