3.8.2.1 Most of a cell’s DNA is not translated (Stem cells)

• Totipotent cells can divide and produce any type of body cell.
• During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.
• Totipotent cells occur only for a limited time in early mammalian embryos.
• • Pluripotent cells are found in embryos
  • multipotent and unipotent cells are found in mature mammals and can divide to form a limited number of different cell types.
• Pluripotent stem cells can divide in unlimited numbers and can be used in treating human disorders.
• Unipotent cells, exemplified by the formation of cardiomyocytes.
• • Induced pluripotent stem cells (iPS cells) can be produced from adult somatic cells using appropriate protein transcription factors
• Induced pluripotent stem cells

  • Produced from adult somatic cells (non-pluripotent, body)
  • Specific protein transcriptional factors associated with pluripotency
  • Causing cell to express genes associated with pluripotency (reprogrammed)
  • Cells are cultured
  • Forms iPS
• Induced pluripotent cells are used in medical treatment because

  • No immune rejection as it can be made using patient's own cells
  • Overcome ETHICAL issues with using embryonic stem cells - as no destruction of embryo and adult can give permission
• Give two characteristic features of stem cells [2 marks]

  • Will replace themselves / keep dividing / replicate
  • Undifferentiated / can differentiate/develop into other cells / totipotent / multipotent / pluripotent (Accept tissues)
• Describe how stem cells become specialised during development

  ● Stimuli lead to activation of some genes (due to transcription factors - see 8.2.2)

  ● So mRNA is transcribed only from these genes and then translated to form proteins

  ● These proteins modify cells permanently and determine cell structure / function
• Explain how stem cells can be used in the treatment of human disorders

  ● Transplanted into patients to divide in unlimited numbers

  • Then differentiate into required healthy cells (to replace faulty / damaged cells)
  • Examples:
  • Potential treatment of Type 1 diabetes by creating healthy islet cells that produce insulin
  • Bone marrow stem cell transplant for SCD / blood cancer
  • Destroy patient’s bone marrow before treatment → so no faulty cells are produced
  • Transplant stem cells from healthy person → divide and differentiate into healthy cells
• Evaluate the use of stem cells in treating human disorders

  For

  ✓ Can divide and differentiate into required healthy cells, so could relieve human suffering by

  saving lives and improving quality of life

  ✓ Embryos are often left over from IVF and so would otherwise be destroyed

  ✓ iPS cells unlikely to be rejected by patient’s immune system as made with patient’s own cells

  ✓ iPS cells can be made without destruction of embryo and adult can give permission
• Evaluate the use of stem cells in treating human disorders

  Against

  X Ethical issues with embryonic stem cells as obtaining them requires destruction of an embryo and potential life (embryo cannot consent)

  X Immune system could reject cells and immunosuppressant drugs are required

  X Cells could divide out of control, leading to formation of tumours / cancer