Most of a cell’s DNA is not translated (A-level only) Flashcards
Stem cells are unspecialised cells. Unspecialised cells are capable of dividing and differentiating into any type of cell. There are four types of stem cell:
Totipotent cells
Pluripotent cells
Multipotent cells
Unipotent cells
Totipotent cells
Totipotent cells exist for only a very limited time during embryonic development in mammals (the first few cell divisions).
During development, totipotent cells translate only part of their DNA.
This means that the cells remain unspecialised.
Totipotent cells are able to produce any type of body cell, as well as cells of supportive structures such as the placenta.
They are the most unspecialised stem cell and specialise into many different cell types.
Pluripotent cells
Totipotent cells develop into pluripotent cells in embryos.
Pluripotent cells are able to divide in unlimited numbers and produce any type of cell that makes up the body.
Pluripotent cells can be used to treat human disorders.
Multipotent cells
Multipotent cells are found in mature mammals.
Multipotent cells can develop into a limited number of cell types.
E.g. Multipotent cells in the bone marrow can produce a range of blood cells.
Unipotent cells
Unipotent cells are found in mature mammals.
Unipotent cells can divide to produce new cells but can only produce one type of cell.
E.g. Cardiomyocytes are unipotent cells that can produce new muscle cells.
How do totipotent cells become specialised?
Totipotent cells become specialised during embryonic development.
When the cells become specialised, only some genes in the cell are activated.
Only the activated genes are expressed.
Proteins in differenciation
If a gene is expressed, it is transcribed into mRNA and translated into a protein.
Differentiation happens as certain proteins are made.
The presence of certain proteins means a cell has become specialised.
Stem cell sources
Stem cells can be taken from three main sources -
Adult stem cells (taken from adult body tissues).
Embryonic stem cells (taken from embryos).
Induced pluripotent stem cells (iPS).
Benefits of using stem cells in disease
There are many benefits to using stem cells in disease.
Stem cells can be used to reduce preventable deaths.
E.g. Stem cells could be used to grow organs for organ transplants to reduce wait times for transplants.
Stem cells can be used to treat conditions that decrease the quality of life.
E.g. Stem cells could be used to replace the damaged cells in the spinal cord that cause paralysis.
Disadvantages of using stem cells
There are some disadvantages to using stem cells.
Obtaining stem cells from embryos is a controversial issue for ethical reasons.
Some people believe using human embryos as source of stem cells is depriving an embryo of life.
Producing iPS cells
Somatic cells are converted to iPS cells by activating genes using appropriate protein transcription factors.
This makes somatic cells become unspecialised so they can be used to treat disease.
iPS cells can be made from a patient’s own body cells.
This also decreases the chance of rejection during transplants (the immune system attacks the cells because they are foreign) because they are their own cells.
Bone marrow transplants
Bone marrow transplants are used to treat blood and immune disorders.
Bone marrow contains multipotent stem cells that can produce all types of blood cell.
Drug research
Stem cells are used to grow artificial tissues.
Drugs can be tested on these artificial tissues before being tested on humans.
Developmental biology
Stem cells can be used to learn more about how an embryo develops and how organs are formed.
Learning about developmental biology can help improve medicine by informing us why organs fail or have abnormalities.
Potential future research
Stem cells can be used to produce new organs or tissue for transplants.
Stem cells can also be used to treat irreversible diseases (e.g. diabetes or paralysis).
Stem cells could be injected at the site of the disorder or problem and encouraged to differentiate into the required specialised cell.
