stem cells

totipotent cells

- can become any type of cell (e.g. can make an entire organism: any body cell type plus extra-embryonic / placental cells)
- during development, totipotent cells translate only part of their DNA, resulting in cell specialisation
- totipotent cells occur only for a limited time in mammalian embryos

stem cells

- undifferentiated cells
- they can specialise and continually divide by mitosis into other cell types

what makes a cell specialised?

different genes are switched on/off

pluripotent

- can become any body cell type (i.e. can make an entire organism (e.g. late embryonic stem cells and fetal stem cells))
- can divide in unlimited numbers
- can be used in treating human disorders

multipotent

- (is more differentiated) can become more than one type of cell
- e.g. adult stem cells (but not ANY cell) (e.g. adult stem cells and umbilical cord blood stem cells) like Hematopoetic stem cells in bone marrow

unipotent

specialised - can only become 1 cell type, e.g. cardiomyocyte

induced pluripotent stem cells (iPS)

- can be produced from unipotent cells (which are fully differentiated)
- unipotent cells are genetically altered in a lab to become pluripotent
- this involves adding protein transcription factors to switch on genes

what makes a cell specialise?

- proteins from cytoplasm, called transcription factors, that attach to a promoter region of the DNA
- the RNA polymerase enzyme can now bind, forming a transcription initiation complex
- transcription can now begin
- transcription will only occur if all the TFs are present - this is how genes can be switched on (allowing control of gene expression)
- mRNA is then produced during transcription and translated into a polypeptide at ribosomes

what is a transcription factor?

1. protein that moves from cytoplasm to DNA
2. TF binds to specific promoter
3. allows binding of RNA polymerase to DNA

advantages of treating a genetic disease with iPS

- use of iPS cells is long-term cuz the undifferentiated iPS cells can keep dividing and differentiating to develop into required cells (gene therapy short-term)
- less chance of rejection/immune response
- just a single treatment (gene therapy requires regular, frequent treatment)
- gene therapy can cause harmful side effects, e.g. from using viruses

disadvantages of treating genetic disease with iPS

- continually dividing cells may cause cancer (uncontrolled cell division)
- (but that cancer might be easily treatable, low risk of getting that cancer)

where are pluripotent, multipotent and unipotent cells found?

in mature mammals