AQA A Level Biology复习笔记8.2.3 The Use of Stem Cells

Use of embryonic stem cells

• Due to their ability to differentiate into multiple cell types, stem cells have huge potential in the therapeutic treatment of disease and producing transplants
• For many countries, such as the USA and those within the EU, the use of embryonic stem cells is banned, even for research
• In other countries, such as the UK, the use of embryonic stem cells is allowed for research but is very tightly regulated
• Embryonic stem cells can be one of two potencies:
  • Totipotent if taken in the first 3-4 days after fertilisation
  • Pluripotent if taken on day 5

   

• The embryos used for research are specifically donated for this purpose
  • These embryos are fertilised in vitro

   

Use of multipotent adult stem cells

• Adult stem cells can divide (by mitosis) an unlimited number of times but they are only able to produce a limited range of cell types
• A small number of adult stem cells are found in certain tissues within the body such as:
  • Bone marrow - used to produce different types of blood cell
  • Brain - used to produce different types of neural and glial cells

   

• However, small numbers of stem cells (known as adult stem cells) remain to produce new cells for the essential processes of growth, cell replacement and tissue repair
• Research is being carried out on stem cell therapy, which is the introduction of adult stem cells into damaged tissue to treat diseases (eg. leukaemia) and injuries (eg. skin burns)
• The use of adult stem cells is less controversial than embryonic stem cells because the donor is able to give permission
  • For example, many people donate bone marrow to help treat leukaemia patients

   

• However, if multipotent stem cells are being donated from one person to another they need to be a close match in terms of blood type and other body antigens
  • There is a chance that the cells used are rejected by the patient's immune system

   

Table showing the types of stem cell

Use of induced pluripotent stem (iPS) cells

• iPS cells have been developed by scientists using an adult's somatic cells that are unipotent (fully differentiated)
• As all somatic cells contain the same genetic material scientists are able to use specific transcription factors to target the genes that control pluripotency
  • Scientists 'switch on' these genes that are usually silenced in differentiated cells which allows them to revert back to pluripotent cells

   

• The resultant pluripotent cells can then be used to produce any type of cell required for repair/treatment of the body
• iPS cells could therefore be used instead of embryonic cells
  • This would avoid the ethical issues associated with using embryonic stem cells

   

• However, this technique is not verified yet as during research iPS cells have caused tumour formation
  • This is thought to be because some of the genes switched on will control the cell cycle and its regulation, which if uncontrolled will lead to tumour formation

   

Table showing the uses of stem cells in Type 1 Diabetes and Paralysis

Table evaluating the use of stem cells