Mitosis

Mitosis is a type of the cell division. Before mitosis starts, it is necessary to replicate the chromosomes. The parts which are created during the replication are called "sisters chromatids". Later, they are separated by the mitotic spindle. The whole process takes about 160 minutes.

Mitosis has several phases that take place one after the other. They are called prophase, prometaphase, metaphase, anaphase and telophase.

Prophase

 * chromosomes are the most condensed;
 * they look like we know them from the karyotype;
 * the mitotic spindle is being created outside the cell;
 * the movement of the centrosomes is caused by the interaction of proteins and microtubules;
 * time: 90 minutes.



Prometaphase

 * the cell is losing its nuclear membrane and chromosomes bind to the mitotic spindle;
 * chromosomes are bound by the microtubules and proteins complexes called kinetochors (these proteins are located in the centromeres);
 * microtubules are formed from the nuclear membrane;
 * each sister chromatid has its own kinetochor (so there are two kinetochors on one chromosome).



Metaphase

 * all chromosomes move to the equatorial line;
 * this movement is caused by creating and destroying the proteins which form the microtubules – this process is called "dynamic instability";
 * any failure of the connecting leads to incorrect dividing of the chromatids and some chromosomal abnormality;
 * time: 20 minutes.



Anaphase

 * the sisters chromatids are divided by the proteolytic enzymes;
 * each of them is then transfered to the opposite part of the cell – this is caused by the depolymeration of the microtubules;
 * sister chromatid becomes the daughter chromosome;
 * time: 10 minutes.



Telophase

 * the nuclear membrane appears again;
 * the condensed chromosomes change into their interphase state;
 * the transcription can now continue;
 * from one parent nucleus two daughter nuclei are created;
 * time: 45 minutes.

Multinucleated Cells

 * A multinucleated cell occurs when the its nucleus has divided normally, but the cytoplasm did not divide. Such cells look giant and have several nuclei. E.g. xanthoma

Syncytial Cells

 * Several cells fuse together.

Increased Rate of Mitosis

 * This is typical in tumours – e.g. sarcoma or Hodgkin Lymphoma.

Damage by the External Influences

 * 1) during mitosis – we can find multipolar spindle;
 * 2) in the resting cells – fragmentation of the chromosomes or forming of the micronuclei.

Related articles

 * Karyotype
 * The Cell Cycle
 * Meiosis