stem cells

• stem cells: unspecialised cells that can develop into other types of cells
• totipotent: can divide into any type of cell, only found in first few divisions of embryo
• pluripotent: can specialise into any cells except placenta, found in embryo after first few divisions
• multipotent: differentiate into a few different cell types
• unipotent: can only specialise into one cell type
• how stem cells specialise:

  • stem cells contain all the same genes
  • under correct conditions, some of these genes are expressed and others switched off
  • mRNA is transcribed from these certain genes, then translated into proteins
  • these proteins modify the cell - determine structure and control cell processes
  • these specialise the cell, which is difficult to reverse
• cardiomyocytes:

  • unipotent stem cells
  • heart muscle cells can not divide to replicate themselves
  • instead, damaged heart tissue can be replaced from a small supply of unipotent stem cells in the heart
  • however, speed of process is undetermined; either all cells are replaced repeatedly, or only some are replaced and others are never
• stem cells in treatment:

  • spinal cord injuries - replace damaged nerve tissues
  • heart disease / damage from heart attacks
  • bladder conditions - grow whole bladder
  • respiratory diseases - grow windpipe
  • organ transplants - grow and transplant organ
• stem cell therapies:

  • stem cells in bone marrow can specialise into any blood cell
  • bone marrow transplants can replace faulty bone marrow that produces abnormal blood cells
  • treats leukemia or sickle cell anemia
• ethical issues of stem cells:

  • obtaining embryonic stem cells involves destroying embryos
  • at fertilisation, embryo has right to life
  • egg can be artificially activated instead of fertilised
  • adult stem cells only multipotent
  • induced pluripotent can be made from own cells; less chance of rejection
  • induced pluripotent made from adult stem cells and have same flexibility as embryonic stem cells
• adult stem cells:

  • from adult tissue
  • obtained by simple operation
  • can only specialise into certain cells (multipotent)
• embryonic stem cells:

  • embryos created via IVF
  • once embryos are 4-5 days old, stem cells removed and embryo is destroyed
  • can divide unlimited number of times
  • pluripotent
• induced pluripotent stem cells:

  • adult cells made to express a series of transcription factors; now express genes associated with pluripotency
  • modified virus infects adult cell, passing pluripotent genes into adult DNA
  • needs more research into how similar these are to embryonic stem cells