Apoptosis- Programmed Cell Death

• Cancer cells


  cells which have a mutation in their regulation of apoptosis- they become immortal
• How is apoptosis triggered?

  • Triggered by cell death signals which can come from inside or outside the cell.
  • Carefully controlled by caspase enzymes
• Extrinsic pathway of apoptosis

  • can be triggered by natural killer cells that have detected abnormal behaviour
  • These ligands bind to surface receptors, causing a conformational change inside the cell.
  • This acts as signal transduction and activates a protein cascade which produces caspase.
• intrinsic pathway of apoptosis

  • can be triggered by DNA damage or the presence of an abnormal protein like p53
  • Activates a caspase cascade
  • cells may initiate apoptosis if certain factors required for growth are not present.
• Caspases


  Start inactive and then are activated through post-translational modification.

  Proteolytic cleavage removes subunits and reassembles them to form active caspases
• Caspase cascade


  initiated by an inhibitor caspase and executioner caspases degrade DNA, keratin and actin

  Each executioner can degrade over 600 components
• When is apoptosis essential?

  during the development of an organism to remove cells no longer required as development progresses or during metamorphosis
• what happens to the cell after apoptosis?


  the small parts are then engulfed by white blood cells