All cells arise from other cells

• Binary fission


  - Involves circular DNA & plasmids replicating

  - cytokinesis creates two daughter nuclei

  - each daughter cell has one copy of circular DNA and a variable number of plasmids
• Cell cycle


  1) Interphase (G1, S, G2)

  2) nuclear division - mitosis or meiosis

  3) cytokinesis
• Interphase


  - Longest stage in the cell cycle when DNA replicates (S-phase) and organelles duplicate while cell grows (G1&G2-phase)

  - DNA replicates and appears as two sister chromatids held by centromere
• Mitosis


  - One round of cell division

  - two diploid, genetically identical daughter cells

  - growth and repair (e.g. clonal expansion) - comprised of prophase, metaphase, anaphase and telophase
• Prophase


  - Chromosomes condense and become visible

  - nuclear envelope disintegrates

  - in animals - centrioles separate & spindle fibre structure forms
• Metaphase


  - Chromosomes align along equator of cell

  - spindle fibres released from poles now attach to centromere and chromatid

  
• Anaphase


  - Spindle fibre contracts (using ATP) to pull chromatids, centromere first, towards opposite poles of cell

  - centromere divides in two

  
• Telophase


  - Chromosomes at each pole become longer and thinner again

  - spindle fibres disintegrate + nucleus reforms

  
• Mitotic index


  Equation - number of cells in mitosis/total number of cells

  - Used to determine proportion of cells undergoing mitosis

  - Calculated as a percentage OR decimal x100 for percentage