apoptosis

• Apoptosis


  Programmed (regulated) cell death, purpose is to remove cells that are no longer needed or that may be a threat
• Apoptosis


  1. Cell receives a signal either from outside (death receptor pathway) or inside (mitochondrial pathway)

  2. Leads to activation of caspases (enzymes)

  3. Results in breakdown of the cell
• Examples of apoptosis


  • Webbing between fingers
  • Excess immune cells after infection is cleared
  • Damaged cells, cancer cells, infected cells (virus), cells with UV damaged DNA
  • Old cells
• Necrosis


  A process that results in cell death that is not controlled, it results in the release of substances that cause inflammation and will cause damage to the surrounding cells
• Necrosis vs apoptosis


  Necrosis can result in tissue damage
• Mitochondrial pathway (intrinsic - inside)


  1. Internal damage (detected in the cell cycle) due to radiation, DNA damage, virus and bacteria infection

  2. Activates transcription and translation of signalling molecules, these travel to and bind to mitochondria making pores in the membrane releasing apoptosis activating factors that activate a cascade of caspases resulting in controlled disassembly of the cell
• Intracellular death signals (mitochondrion - mediated pathway)


  1. Damaged mitochondrion

  2. Activating factors (cytochrome) released

  3. Cascade of caspases activated

  4. Deliberated disassembly of the cell
• Death receptor pathway (extrinsic - outside)


  1. External signal that occurs when a signalling molecules bind to a death receptor of the cell surface

  2. Can be triggered by cytokinesis (immune system chemical messengers), cytotoxic drugs, immune system cells, hormones, pathogens

  3. All cells have transmembrane death receptors

  4. Binding of specific signalling molecules (e.g cytokines) to the death receptor triggers signal transduction and a cascade of caspase activation

  5. Activation of caspases

  6. Cascade of caspases

  7. Deliberate disassembly of the cell
• Caspases


  Enzymes produced in cells and stored in an inactive form, activated in both types of apoptosis (intrinsic and extrinsic pathways), have many functions in the disassembly of the cell in apoptosis including cleaving DNA into fragments, cleaving nuclear cytoplasmic and membrane proteins, dismantling cytoskeleton
• Dismantling of the internal components leads to the cell shrinking and blebs form, results in controlled cell death