Apoptosis

• Mitosis in cell division type that produces identical new cells for growth, cell replacement and tissue repair; Apoptosis is programmed cell death, and is constantly replacing/destroying cells through early development
• Mitosis: Cell cycle section regulated by homeobox and hox genes, every cell in organism has all DNA and all needed genes; in cell differentiation some are switched off (cannot be expressed), remember normal body cells can only divide 50 times before dying
• Apoptosis: Induced to commit suicide, Necrosis: Killed by injury (mechanical damage, infection, toxic chemical exposure) of infection
• In necrosis, cells undergo changes: cell and organelles swell (plasma membrane can’t control ion and water passage), cell contents lack out, inflaming surrounding tissue
• Integral for proper development (e.g. removal of tadpole tail, removal of tissue between fingers and toes in foetus, menstruation, creation of neuronal connections)
• Destroy cells threatening to organism integrity (e.g. kill virus-infected cells, prevent autoimmune cells, kill cell’s with damaged DNA or cancerous cells)
• Regulated by hox genes; expression regulated by stimuli:

  • Internal: DNA damage (detected in cell cycle), signalling (cytokines, hormones, growth factors and nitric oxide) or psychological stress
  • External: Light intensity, temperature, pathogen, lack of nutrients or drugs (e.g. thalidomide)