Stem Cells Flashcards
What is a stem cell?
A non-specialised cell which can divide and differentiate into a range of others
What enables stem cells to differentiate?
The express all 23,000 (in humans) genes
Stem cell mitosis produces?
2 different daughter cells. One identical to the parent cell and one that is a precursor cell that can differentiate further to be come a specialised cell.
Which is the process of mitosis called in stem cells?
Asymmetrical cell division
Three sources of stem cells?
Embryonic stem cells produced during IVF and embryonic stem cells produced by therapeutic cloning
Adult stem cells e.g. in bone marrow
Induced pluripotent stem cells
How are embryonic stem cells produced by IVF?
Sperm cell injected into egg cell
12 hours: the two bundles of genetic material are visible
20 hours: genetic bundles combine
Day 2: egg cell divides into two identical daughter cells and then again to 4
Day 3: eight cell embryo, all cells totipotent
Day 4: mass off identical cells, all still totipotent
Day 5: now called a blastocyst (100 cells) outer layer of cells becomes placenta( differentiation starts to occur), inner cells become foetus
Totipotent meaning?
Can differentiate to any type of cell including placental cells
Pluripotent meaning?
Can differentiate to any type of body cell (not placenta), fewer genes are active compared to totipotent
What do growth factors do?
Turn on genes required for the specialised cell and turn all the other genes off
Advantages of embryonic stem cells produced by IVF?
Pluripotent
Plentiful supply
Disadvantages of embryonic stem cells produced by IVF?
Embryos destroyed- potential life
Rejected by the immune system
How are stem cells from therapeutic cloning produced?
1) DNA removed from donor egg cell and DNA from the patient cell is put into the egg cell
2) egg cell given small electric shock to make the egg think it has been fertilised by a sperm
3) egg cell divides and differentiates into an early embryo
4) extract stem cells from inner cell mass
Advantages of embryonic stem cells produced by therapeutic cloning?
Pluripotent
Genetically identical to patient so no rejection issues
Disadvantages of embryonic stem cells produced by therapeutic cloning?
Embryos created with no intention of life
Technique could be used to clone humans (illegal)
Cell specific gene expression meaning?
Specialised cells only have the genes needed active and the rest are switched off