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