7.3 stem cells

• stem cells


  • undifferentiated cells
  • ability to divide and differentiate into specialised cells
• 3 types of stem cells:

  • totipotent
  • pluripotent
  • multipotent
• totipotent cells


  • differentiate into any type of cell in body + placenta
  • found in zygote
• pluripotent cells


  • can differentiate into any cells except cells in placenta + embryo
  • found in blastomeres
• multipotent cells


  • can differentiate into only a few type of cells
• stem cells can replace damaged cells or tissues
• Sources of embryonic stem cells

  • pluripotent stem cells from blastocysts
  • in IVF treatment
  • requires consent from parents
• strengths of using embryonic stem cells

  • can differentiate into most types of cells
  • provides cells for drug testing, don't need to use animals.
• weaknesses of using embryonic stem cells

  • chance of rejection`
  • risk of infection and potential cancer
• Ethical issues using embryonic stem cells

  • certain groups against it
  • death of a potential life
  • can't gain consent from embryo
• other side of argument of using embryonic stem cells (+)

  • benefits outweigh harm
  • embryos would be discarded anyway
  • reduces need for embryo in future
• adult stem cells

  • multipotent
  • avoids ethical issues
  • used for bone marrow transplants
• issues with adult stem cells

  • chance of rejection
  • hard to grow
  • not everyone has stem cell reserves
• induced pluripotent stem cells

  • alternative to embryonic stem cells
  • reprogrammed fibroblast to be pluripotent again
  • no ethical issues
• formation of iPS cells:


  • fibroblast cells in connective tissue used
  • 4 genes inserted in a virus vector
  • coding for transcription factors
  • which switch on other genes and become pluripotent
• strengths of iPS cells:

  • made from patients own fibroblast so no chance of rejection
  • no ethical issues
• issues with iPS cells:

  • potential of causing cancer
  • viral vector use is risky
  • expensive equipment
• solution for iPS cells:

  • proteins can be used instead of genes
  • therefore safer + more reliable
• how do stem cells differentiate?

  • through epigenetic modification
  • via dna methylation and acetylation
  • housekeeping genes remain on
  • specific gene needed for differentiation switches on