Mitosis

• Cell cycle

  The process by which cells divide to produce two genetically identical daughter cells
• Interphase

  1. G1 phase (gap phase 1)

  2. S phase (synthesis)

  3. G2 phase (gap phase 2)
• G1 phase


  • Cell growth
• S phase

  • DNA synthesis
  • DNA in cell replicates
• G2 phase


  • Cell continues growing
  • Makes proteins and organelles
• Interphase is the longest part of the cell cycle
• Mitosis


  Where eukaryotic cells divide and produce two daughter cells
• Each daughter cell contains identical copies of DNA produced by the parent cell during DNA replication (in the S phase of interphase)
• Behaviour of chromosomes during prophase

  1. Chromosomes condense and become visible

  2. Become shorter and fatter

  3. Free in the cytoplasm once nuclear envelope breaks down
• Formation of spindle fibres during prophase

  1. Bundles of proteins called centrioles separate and move to opposite ends/ poles of the cell

  2. Form network of protein fibres called spindle
• Nuclear envelope during prophase

  Envelope disintegrates/ breaks down
• Behaviour of chromosomes during metaphase

  Chromosomes line up at the equator of the cell
• Role of spindle fibres during metaphase

  1. Spindles released from poles

  2. Attach to the centromeres on chromosome
• Chromosomes line up along metaphase plane
• Behaviour of chromosomes during anaphase

  1. Centromeres divide

  2. Individual sister chromatids are pulled to opposite poles of the cell

  3. Separated sister chromatids called chromosomes
• Role of spindle fibres during anaphase

  1. Spindle fibres contract

  2. Pulling the chromatids to opposite poles of the cell

  3. Results in v shape of chromatids
• Anaphase requires energy in the form of ATP
• Behaviour of chromosomes during telophase

  1. Reach opposite poles of the cell

  2. Uncoil and become long and thin
• Nuclear envelope during telophase

  1. Begins to reform around each group of chromosomes

  2. Two nuclei
• Cytokinesis

  Cytoplasm divides resulting in two genetically identical daughter cells
• Role of spindle fibres during telophase

  Disintegrate
• Uncontrolled cell division

  Leads to the formation of tumours and cancers
• Many cancer treatments are directed at controlling the rate of cell division
• Cancer treatments

  • Disrupt the cell cycle
  • Kill the tumour cells
• Cancer treatments are unable to distinguish between healthy body cells and tumour cells
• Tumour cells divide more rapidly than healthy cells, so most treatments against them are often effective
• Ways treatments can target the cell cycle

  • Chemotherapy prevents the synthesis of enzymes needed for DNA replication during G1 phase. Cell is therefore unable to enter synthesis phase - forcing it to kill itself
  • Radiation and some drugs might damage DNA before and during S phase the DNA is checked for any damage. If damage is detected the cell will kill itself preventing the growth of any further tumours
• Binary fission in prokaryotic cells

  1. Replication of the circular DNA and of plasmids

  2. Division of the cytoplasm to produce two daughter cells

  3. Each with a single copy of the circular DNA and a variable number of copies of plasmids
• Viruses don't undergo cellular division because they're non-living
• How viruses like HIV replicate

  1. Injection of their nucleic acid into host cell

  2. The infected host cell replicates the virus particles