Stem cells

• Stem cell


  Undifferentiated cells that can divide indefinitely & turn into other specific cell types
• Types of stem cells


  • Totipotent
  • Pluripotent
  • Multipotent
  • Unipotent
• Totipotent


  Can divide & produce into any cell type; occur for a limited time in early mammalian embryos
• Pluripotent


  Can develop into any cell type excluding the placenta; found in embryos
• Multipotent


  Can only develop into a few different types of cell
• Unipotent


  Only develop into 1 type of cell
• Totipotent cells during embryonic development


  1. Certain parts of the DNA are selectively translated

  2. Only some genes are 'switched on', in order to differentiate the cell into a specific type and form the tissues that make up the foetus
• Pluripotent cells


  • They can divide in unlimited numbers, & can thus be used to repair or replace damaged tissue
• Unipotent cell


  A cell that can only develop into one type of cell. This happens at the end of specialisation when the cell can only propagate its own type
• Unipotent cell example


  • Cardiomyocytes (heart cells)
• Stem cells location


  • Embryos (Totipotent & pluripotent)
  • Mature cells (Multipotent & unipotent)
• Uses of stem cells


  • Medical therapies e.g. bone marrow transplants, treating blood disorders
  • Drug testing on artificially grown tissues
  • Research e.g. on formation of organs and embryos
• How induced pluripotent stem cells are produced (iPS)

  1. From mature, fully specialised (somatic) cells

  2. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors
• Transcription factor


  A protein that controls the transcription of genes so only certain parts of the DNA are expressed
• How transcription factors work


  1. Move from the cytoplasm into the nucleus

  2. Bind to promoter region upstream of target gene

  3. Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases rate of transcription
• Control by oestrogen in regulating transcription

  1. Oestrogen diffuses across the cell membrane & binds to a receptor on a transcription factor

  2. This alters the shape of the DNA binding site on the transcription factor & makes it able to bind to the DNA

  3. The transcription factor enters the nucleus via the nuclear pore & binds to DNA; stimulates the transcription of the gene that makes up the DNA
• Small interfering RNA ~ used for short term switching off of genes


  1. The siRNA binds to a complementary sequence of mRNA

  2. The cell detects the double stranded form on mRNA & views it as abnormal

  3. The mRNA is broken down by enzymes preventing translation