3 of 6

Write now Article Tools

INTRODUCTION
The mitosis is a cellular division process generating two identical cells from a mother cell given that all its chromosomal material is exactly duplicated, if a genetic mutation doesn't occur.
With this process, the multi-cellular organisms can grow, renew their tissues and reproduce, while the mono-cellular organisms (bacteria, fungi, algae) can form big colonies.

During the mitosis, the nucleus and cytoplasm are split in two equal parts (CYTODIERESIS), with the help of two particular structures:
- The NUCLEOSPINDLE, formed by many thin protein fibers, extended between the two poles of the cell.
- The CENTRIOLES, little organs typical of animal cells, placed outside the nucleus and duplicated during the mitosis.

THE STAGES OF MITOSIS
This process is normally divided in 4 phases with other sub-phases:

1) PROPHASE
The DNA of the chromosomes is already duplicated to form identical filaments that are condensed so that they appear at the microscope as two identical sticks, the CHROMATIDES, united in one only point, the CENTROMER.
The nucleospindle starts to form and the nuclear membrane is broken from the inside.

2) METAPHASE
The nucleospindle is formed with all its filaments nearly parallel and their extremities united and, moving along it, the chromosomes places themselves along the the equatorial plane of the cell, ready to go to opposite directions.

3) ANAPHASE
The two chromatides of a chromosome split off and move each one toward the opposite poles of the mitotic nucleospindle.

4) TELOPHASE
The chromatides of every chromosome have reached the poles and the nucleus membrane forms again within the two new cells, after that the two nuclei are totally formed.
At this point, the nucleospindle fades away and the chromosomes are again in the apparently confused form of chromatin.

The chromatin, in reality, is a network of fibers containing the DNA filaments.
So, the nucleus, when not undergoing a mitosis, is formed by DNA (40%), proteins associated to it (57%) and RNA (13%) that is bound to DNA.

When the mitosis starts, the chromatin is condensed in regular and stable structures, the chromosomes and every species of living being forms them in various amounts.
This structure of the nucleus is present in the animal cells (EUKARYOTE) and absent in the BACTERIA (PROKARYOTE).
Just the bacteria are able to produce a mitosis within few minutes and, after 15-30 minutes, they are again able to duplicate.
With this rate, after 24 hours, a single cell can produce 280,000 billions of cells by means of an exponential multiplication!

Instead, the animal cells, part of multi-cellular organism, have a much more controlled replication rate with the mitosis, that is limited by the same organism.
When this control mechanism fails, the mitosis in a tissue occurs without control: this is a cancer.

Learn more about this author, Aldo Bonincontro.
Click here to send this author comments or questions.

Add your voice

Know something about The stages of a mitotic cell cycle?
We want to hear your view. Write now!