2.2 all cells arise from other cells

• Interphase

  S phase – DNA replicates semi-conservatively leading to two sister chromatids joined at a centromere

  • G1 and G2 – Number of organelles and volume of cytoplasm increases; protein synthesis; ATP content increased

  
• Mitosis

  • nucleus divides
  • to produce 2 nuceli with IDENTICAL copies of DNA produced by parent cell
  • Stages - ‘PMAT’
• Cytokinesis

  • The division of the cytoplasm and cell membrane, producing two new GENETICALLY IDENTICAL DAUGHTER CELLS
• The importance of mitosis in the life of an organism?

  
  

  Parent cell divides to produce 2 genetically identical daughter cells for…

  
  

  • Growth of multicellular organisms by increasing cell number
  • Repairing damaged tissues / replacing cells
  • Asexual reproduction
• Mutation in DNA/genes controlling mitosis can lead to uncontrolled cell division, tumour is formed if this leads in MASS OF ABNORMAL CELLS

  Uncontrolled cell division can lead to the formation of tumours and of cancers

  -Malignant tumour – cancerous – spreads and affects other tissues / organs

  • Benign tumour – non-cancerous
• Many cancer treatments are directed at controlling the rate of cell division

  Disrupt the cell cycle – cell division / mitosis slows – tumour growth slows - Prevent DNA replication → prevent / slows down mitosis - Disrupts spindle activity / formation → chromosomes can’t attach to spindle by their centromere → sister chromatids can’t be pulled to opposite poles of the cells → prevent/slow mitosis

   ☺

  Disrupt cell cycle of normal cells too, especially rapidly dividing ones e.g. cells in hair follicles

  Drugs more effective against cancer cells because dividing uncontrollably / rapidly
• Binary fission

  Circular DNA and plasmids replicate (circular DNA replicates once, plasmids can be replicated many times)

  Cytoplasm expands (cell gets bigger) as each DNA molecule moves to opposite poles of the cell

  Cytoplasm divides

  • = 2 daughter cells, each with a single copy of DNA and a variable number of plasmids
• Viral replication

  Viruses don’t undergo cell division because they are non-living

  1. Attachment protein binds to complementary receptor protein on surface of host cell

  2. Inject nucleic acid (DNA/RNA) into host cell

  3. Infected host cell replicates the virus particles-

  • NUCLEIC ACID REPLICATED
  • cell produces viral protein/ Caspid/enzymes
  • virus assembled then released
• Prophase?


  Chromosomes condense, becoming shorter

  and thicker (so visible) = appear as two

  sister chromatids joined by a centromere

  • Nuclear envelope breaks down and centrioles move to opposite poles forming spindle network

  
• METAPHASE?

  • spindle fibres attach to chromosomes by centromeres so chromosomes alight along equator

  
• Anaphase

  Spindle fibres SHORTEN/ contract

  • Centromere divides
  • pulling chromatid (from each pair) to opposite poles of cell

  
• Telophase

  • chromosome uncoil/becoming longer and thinner
  • nuclear envelope reforms = to produce 2 nuclei with identical copies of DNA produced by parent cell
  • spindle fibres/ centrioles break down

  
• Why do some eukaryotic cells not undergo the cell cycle ?

  within multicellular organisms, not all cells retain the ability to divide, e.g neurons .

  only that do go through CELL CYCLE
• Suggest how cancer treatment control rate of cell division?

  • 1.Some disrupt spindle fibre activity/formation -
  • -so chromosome can’t attach to spindle fibre by their centromere
  • -so chromatids can not be separated to opposite poles (no anaphase) so prevents mitosis
  • 2. some prevent DNA replication during interphase
  • -so can’t make two copies of each chromosome(chromatids) so prevents/slow mitosis
  • disadvantage- disrupts cell cycle of rapidly dividing healthy cells
• DOES CYTOKINESIS ALWAYS HAPPEN?

  Some cells ( muscle cells) undergo mitosis without cytokinesis ( cytoplasmic reticulum) so have multiple nuclei