Mitosis is the division of a cell that results in 2 daughter cells which have identical copy of the DNA of the parent cells. Mitosis occurs only in ‘body cells’ (e.g. muscle, epithelial tissue etc.) compared to meiosis which only occurs in the production of gametes. Mitosis produces diploid cells compared to meiosis which produced haploids.

The 4 phases of mitosis include:

 

  • Prophase: Chromosomes become visible, nuclear envelope disintegrates, nucleolus disappears
    • Nucleus disappears, the chromosomes become visible in their super coiled state
    • Spindle fibres produced by the centrioles
  • Metaphase: Chromosomes line up on the centre of the cell
    • Chromosomes are seen to be made up of 2 chromatids. Each chromatid is identical to the parent cell
    • Chromatids are joined by centromere
    • The chromatids are aligned across the equator of the cell
  • Anaphase: Spindle fibres attach to the chromatids. Chromatids are pulled together towards the poles
    • Centromere divides into 2
    • Spindle fibres pull individual chromatids making up the chromosome parts
    • The chromatids move rapidly to the opposite poles of the cells, they are now referred to as chromosomes
  • Telophase: Chromosomes reach poles become indistinct. Nuclear envelope forms as well as nucleolus. Spindle fibres disintegrate
    • Chromosomes become longer and thinner widely spread chromatids
    • The spindle fibres disintegrate and the nucleus envelope and nucleolus form
    • The cytoplasm divides in a process called cytokinesis

 

Prokaryotic Cell Division

  • Prokaryotic reproductions is called Binary Fission.
  • This involves:
  • The circular DNA molecules replicates and both copies attach to the cell membrane
  • The plasmids replicate
  • The cell membrane begins to grow between the two molecules of NDA, dividing the original cells into the 2 daughter cells. This also divides the cytoplasm as well.
  • A new cell wall forms between the two molecules of DNA, dividing the original cells into two identical daughter cells, each with a single copy of circular DNA and a variable number of copies of the plasmids.

 

Virus Replication

  • Viruses are non-living, so they do not undergo cell division
  • This involves:
  • Viruses attach themselves with attachment proteins on their surface
  • They inject nucleic acids into the host cell. Into the host cell
  • Genetic Information is injected with viral nucleic acid then provides the instructions for the host cell metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins
  • They are then assembled into new viruses.