12) Cell Division

• Division/proliferation:

  • Cell division is the process where cells produce daughter cells

   ⤷ Essential process in growth and development, repair and immune response

  ⟶ abnormal growth results in cancer
• Overview of Cell cycle: Sequence of growth, DNA replication and cell division

  1. Interphase - G1, S, G2
  2. M Phase - Mitosis and Cytokinesis (form transient cytoskeletal structures)

   - The mechanical stages of cell division begins at the end of interphase/start of M phase

  
• Cell cycle checkpoints:

  Cell proliferation is controlled by the cell cycle control system

  • Checkpoints between G1-S Phase,  G2-M Phase and M Phase-G1 ensure all previous stages have been completed
• • Kinase transfers phosphate from ATP onto other proteins to cause a conformational change
  • CDKs activity relies on Cyclin
  • CKI are inhibitors of CDK and respond to signals from damaged DNA
  • ⤷ Hence why CDKs are often the target of anticancer drugs to stop cell cycle from forming cancer cells

  
• The rise and fall of Miotic-CDK activity

  • Cyclin-dependent kinases (cdk) are the main cell cycle regulators and fluctuate between stages

   ⤷ Binding of cyclin-cdk stimulates kinase

  ⤷ Cyclins act as “accelerators” and cdks act as engine components
• Mitosis vs Meiosis

   - Mitosis happens in diploid somatic cells

   - Results in genetically identical daughter cells

  Meiosis:

   - Occurs in gametes
• Meiosis 

   - A single cell divides twice to produce 4 haploid daughter cells 

  Meiosis 1: Interphase, PMAT 1

  Meiosis 2: PMAT 2
• Mitosis

   - Cellular proliferation 

   1) Prophase: 

  Chromatin condenses in G2, centrioles divide and spindles form

   1.5) Prometaphase: Nuclear envelope breaks down, spindle has access to chromosomes 

  2) Metaphase:

  Chromosomes align equator of metaphase plate

  3) Anaphase:

  paired chromosomes separate and move along microtubules to opposite poles

  4) Telophase

  Daughter chromosomes arrive at poles of cell, new nuclear envelope forms
• 3 classes of microtubules make up the mitotic spindle 

   1) Aster/Astral: Anchor spindle poles to cell membrane 

  2) Kinetochore: Cross across the centrosome of chromosomes

  3) Interpolar: extending across the cells