What is mitosis?

Mitosis is a process where a single cell divides into two identical daughter cells (cell division). 

  • During mitosis one cell divides once to form two identical cells.
  • The major purpose of mitosis is for growth and to replace worn out cells.
  • If not corrected in time, mistakes made during mitosis can result in changes in the DNA that can potentially lead to genetic disorders.

Mitosis is divided into five phases:  

1. Interphase:

  • The DNA in the cell is copied in preparation for cell division, this results in two identical full sets of chromosomes.
  • Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division.
  • During interphase, microtubules extend from these centrosomes.

2. Prophase: 

  • The chromosomes condense into X-shaped structures that can be easily seen under a microscope.
  • Each chromosome is composed of two sister chromatids, containing identical genetic information.
  • The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on.
  • At the end of prophase the membrane around the nucleus in the cell dissolves away releasing the chromosomes.
  • The mitotic spindle, consisting of the microtubules and other proteins, extends across the cell between the centrioles as they move to opposite poles of the cell.

3. Metaphase:

  • The chromosomes line up neatly end-to-end along the centre (equator) of the cell.
  • The centrioles are now at opposite poles of the cell with the mitotic spindle fibres extending from them.
  • The mitotic spindle fibres attach to each of the sister chromatids.

4. Anaphase:

  • The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole.

5. Telophase:

  • At each pole of the cell a full set of chromosomes gather together.
  • A membrane forms around each set of chromosomes to create two new nuclei.
  • The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
Illustration showing the five stages of mitosis.

Illustration showing the five stages of mitosis.
Image credit: Genome Research Limited

 

This page was last updated on 2016-01-25