Mitosis


Mitosis is the process by which eukaryotic somatic (body) cells divides to produce two genetically identical daughter cells

There are four main processes in eukaryotic organisms which may involve mitosis:

  • Growth:  Multicellular organisms increase their size by  increasing their number of cells through mitosis
  • Asexual reproduction:  Certain eukaryotic organisms may reproduce asexually by mitosis (e.g. vegetative reproduction)
  • Tissue Repair:  Damaged tissue can recover by replacing dead or damaged cells
  • Embryonic development:  A fertilised egg (zygote) will undergo mitosis and differentiation in order to develop into an embryo


Overview of Mitosis



Prophase

  • DNA supercoils, causing chromosomes to condense and become visible under a light microscope
  • As DNA was replicated during interphase, the chromosomes are each comprised of two genetically identical sister chromatids joined at a centromere
  • The centrosomes move to opposite poles of the cell and spindle fibres begin to form between them (in animals, each centrosome contains 2 centrioles)
  • The nuclear membrane is broken down and disappears


Metaphase

  • Spindle fibres from the two centrosomes attach to the centromere of each chromosome
  • Contraction of the microtubule spindle fibres cause the chromosomes to line up separately along the centre of the cell (equatorial plane)


Anaphase

  • Continued contraction of the spindle fibres cause the two sister chromatids to separate and move to the opposite poles of the cell
  • Once the two chromatids in a single chromosome separate, each constitutes a chromosome in its own right


Telophase

  • Once the two sets of identical chromosomes arrive at the poles, the spindle fibres dissolve and a new nuclear membrane reforms around each set of chromosomes
  • The chromosomes decondense and are no longer visible under a light microscope
  • The division of the cell into two daughter cells (cytokinesis) occurs concurrently with telophase