Stem cells

• Stem cells


  A stem cell is an undifferentiated cell than can:

  1. Divide indefinitely to create more stem cells
  2. differentiate to become a specialised cell type in a multicellular organism
• Totipotent 


  -”whole“

  -can become any body cell (including placenta in placental mammals)

  -a zygote is totipotent
• Pluripotent 


  -“many”

  -can become any body cell excluding placenta

  -the inner cell mass of a plastocyte is pluripotent
• Multipotent


  -“several”

  -partially differentiated but can still become multiple related cell types
• Specialised cell


  -allows the cell to conduct a single function efficiently compared to if it had multiple

  -humans have 220 specialised cells
• Atypical cells 


  -striated muscle

  -phloem

  -aseptic fungi

  -red blood cells
• Striated muscle


  Multi-nucleated
• Phloem


  No organelles
• Aseptic fungi


  No clearly defined cells
• Red blood cells


  No nucleus or mitochondria
• How does differentiation happens 


  -in embryo progenitor cells will synthesise and secrete morphogens

  -morphogens will diffuse away from progenitor cells

  > high concentration near progenitor cells

  >low concentration away progenitor cells
• Differentiation 


  High concentration- activate more genes

  low concentration- less genes activated