Cell division 1.6

• Cell cycle phases


  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Mitosis


  • Produces cells which are genetically identical to the parent cell, giving genetic stability
• Reasons for cell division

  • Growth
  • Repairing damaged cells
  • Replacement of old, worn-out cells
  • Asexual reproduction
• Cell cycle


  • Controlled by genes
  • If genes regulating cell cycle are damaged, uncontrolled mitosis can occur, leading to tumours and cancer (oncogenes)
• Mnemonic IPMAT


  Remembers the order of phases in mitosis (Interphase, Prophase, Metaphase, Anaphase, Telophase)
• Cytokinesis


  Division of the cytoplasm to create 2 new genetically identical cells
• Plant cell differences in cytokinesis

  • No centrioles
  • Cell plate (droplets of cell wall material) develops from centre out instead of cleavage from outside in
• Prophase


  1. Chromosomes condense and become visible

  2. Centrioles move to opposite sides of cell in animal cells

  3. Spindle forms from microtubules

  4. Nuclear envelope disintegrates
• Metaphase


  Centromeres of chromosomes attach to spindle and line up on the equator
• Anaphase


  1. Spindle fibres shorten

  2. Centromere separates and individual chromatids are pulled to the poles centromere first
• Telophase


  1. Spindle breaks down

  2. Chromosomes uncoil

  3. Nuclear envelope reforms
• Interphase


  • Time of high metabolic activity
  • Replication of organelles
  • New organelles made
  • Synthesis of ATP and proteins
  • Increase in cell size
• Haploid cells can only divide by mitosis
• Meiosis phases


  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
• Prophase I


  • Chromosomes form bivalents (pairs of homologous chromosomes)
  • Arms of chromatids may cross over forming chiasmata, increasing genetic variation
• Metaphase I


  • Homologous chromosomes arrange themselves in pairs along the equator
• Anaphase I


  • Chromosome bivalents separate as each chromosome is pulled by its centromere towards the opposite pole
• Telophase I


  • Nuclear envelopes reform around the chromosomes at the poles
• In meiosis, prophase II occurs after telophase I
• In meiosis, chromosomes are no longer in pairs and the cells are haploid
• Events in meiosis II occur exactly as in mitosis
• Cytokinesis in meiosis results in 4 genetically varied cells
• Interphase

  is divided into 3 stages:

  G1

  S phase

  G2
• G1 stage

  cell growth and preparation for DNA replication
• S phase

  DNA replication and chromatid duplication occurs

  After DNA replicates it now consists of 2 identical strands joined at a centromere
• G2 stage

  Organelles needed for division are replicated and energy reserves are built up