The Process of Mitosis


Mitosis is the term used to describe cell division for replication. The product
at the end of mitosis is two daughter cells both genetically identical to the
original (parent) cell. This process (mitosis) is used for growth and repair
within an organism (and also for asexual reproduction).

There are five main stages to mitosis, called Interphase, Prophase, Metaphase,
Anaphase and Telophase. Although the process has been divided up into these
stages the process of mitosis is actually continuous.

Interphase --------------------------------------- In this, the first stage the
cell will look just like any other \'normal\' cell although this is far from the
case because very much is actually happening. All cell organelles are being
produced in quantity and the chromosomes - DNA molecules are being copied
exactly. The two identical copies of DNA are called a "pair of chromatids" and
they are linked together by an item called a "chromomere". During this stage a
store of ATP is also built up.

[Best put a labelled diagram of a cell during Interphase here.]

Prophase --------------------------------------- In this second stage changes to
the cell become visible. The chromosomes condense, coiling up to about 5% of
their original length, now clearly visible when a stain is added. The centrioles
move to the opposite poles of the cell and small microtubules around the
centrioles become visible (called "Asters"). The nuclear membranes and nucleolus
disintegrate after passing their nucleic acids to certain pairs of chromatids.
Now a spindle forms, this is also made out of microtubules.

[A labelled diagram of the end of the Prophase stage of a cell here would be
great.]

Metaphase --------------------------------------- During this stage the
chromosomes move towards the equator of the spindle, attaching themselves
horizontally by the centromere to the spindle\'s filaments. The chromatids then
pull slightly away from each other at the centromere towards the opposite poles
of the cell.

[A labelled diagram of Metaphase here, and put a note next to it saying "Note
that some spindle fibres run from pole to pole while others from pole to
equator."]

Anaphase --------------------------------------- Now this stage is very quick.
The pairs of chromatids are separated and each chromatids is pulled is pulled
towards each opposite pole by the spindle fibres by a ratchet-like mechanism.
This process requires energy so the ATP store is now used up.

[A labelled diagram of Anaphase. Write a note underneath saying "They split
apart by the centromere breaking into two. Each centromere divides into two so
that each chromatid has its own centromere."]

Telophase --------------------------------------- The chromatids are destined to
become the new chromosomes of the daughter cells. Once the chromatids are at the
poles of the cell they unwind into chromatin again, now becoming hard to see
once again. The spindle fibres now disintegrate and new nuclear membranes form
around the new groups of chromatin making two new nucleus\'. The centrioles now
also replicate and divide their numbers evenly around each nucleus. Now the cell
is ready to divide.

[Draw a diagram of Telophase stage.]

Mitosis is now over. The cell is now ready to divide, by the process known as
"Cytokinesis".

Category: Science