Mitosis

This lesson covers:

  1. The importance of mitosis in living organisms 
  2. The stages of mitosis 
  3. The process of cytokinesis 

Mitosis and cytokinesis

Once cells have completed interphase, they are ready to undergo mitosis and cytokinesis. 

Diagram showing the cell cycle with interphase, mitosis, and cytokinesis stages.

Both of these phases involve divisions: 

  • Mitosis - The nucleus divides.
  • Cytokinesis - The whole cell and cytoplasm divides. 

Importance of mitosis 

Mitosis is a type of cell division in which a parent cell divides to produce two genetically identical daughter cells. Each of these daughter cell contains the same DNA as the original parent cell. 


Mitosis is used by multicellular organisms for many processes, including: 

  • Growth - Unicellular zygotes can divide by mitosis to form multicellular organisms.
  • Replacement of damaged or dead tissues - Cells are constantly dying and being replaced using mitosis. 
  • Asexual reproduction - Some organisms reproduce using mitosis to form genetically identical offspring.
  • Development of body plans - Mitosis is used to form the different parts of an organism.
  • Production of stem cells - Stem cells divide by mitosis. 

Stages of mitosis

Mitosis is one continuous process, but is often described as a series of four stages.

Diagram showing the stages of mitosis including prophase, metaphase, anaphase, and telophase.

Remember that cells have already replicated their DNA during interphase and each chromosome is made up of two identical sister chromatids.

Diagram showing stages of mitosis with centrioles and spindle fibres.

Prophase

The chromosomes condense (become shorter and thicker) and are now visible under a microscope.


Centrioles (bundles of protein) migrate to opposite poles (sides) of the cell. Each centriole starts forming spindle fibres.  


The nucleolus disappears and the nuclear envelope starts to break down, leaving the chromosomes free in the cytoplasm.

Diagram showing the stages of mitosis with chromosomes and spindle fibres.

Metaphase

The chromosomes line up at the equator (middle) of the cell.


Each chromosome attaches to the spindle by their centromere. 


At the metaphase checkpoint, each chromosome is checked to ensure it is attached to the spindle. 

Illustration showing the stages of mitosis with chromosomes and spindle fibers.

Anaphase

The centromeres divide to separate each pair of sister chromatids. 


The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell. 


Each chromatid is pulled by its centromere, causing them to take on a 'V' shape when viewed under a microscope. 

Illustration showing the stages of mitosis with two cells, each containing chromosomes and centrioles.

Telophase

The chromatids reach the opposite poles of the cell where they uncoil to become long and thin chromosomes again. 


A nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform.

Cytokinesis

After the steps of mitosis, the cytoplasm divides in a process known as cytokinesis. This produces two daughter cells that are genetically identical to one another. 

Illustration showing the process of cytokinesis where the cytoplasm divides to form two genetically identical daughter cells.