Cell differentiation
Stem cells are unspecialised and they can develop into any type of cell.
Totipotency which is when it has the ability to produce all cell types including the specialised cells in an organism and extra-embryonic cells.
The second type is Pluripotency which has the ability to produce all the specialised cells, but not extra-embryonic cells.
Totipotency cells are only available in very early stages of the embryo in humans. When there are only 8 cells, this occurs after three divisions.
Five days after conception, a hollow ball of cells called the blastocyst forms. The outer cells of the blastocyst form the placenta. The 50 or so cells inside this form the tissue of the developing embryo, these are known as pluripotent embryonic stem cells.
Multipotent stem cells are those which still have the capacity to give rise to different cell types, such as neural stem cells.
How stem cells work:
- Stem cells all contain the same gene, but not all of them are expressed because some are ‘switched’ off.
- Under the right conditions some genes are activated and others inactive.
- mRNA is only transcribed from the active gene.
- The mRNA from the active genes is then translated into proteins.
- These proteins modify the cell- they determine the cell structure and control cell processes.
- Changes to the cell produced by these proteins causes the cell to become specialised. These changes are difficult to reverse.
Some stem cell treatment already exists, such as treatment for leukaemia, where bone marrow transplants are given. Scientists are researching treatments for injuries such as: spinal cord injuries, and heart disease. The treatments can save many lives, and also improve the quality of lives for many people.
There are two methods from where stem cells can come from, these are Adult stem cells and embryonic stem cells.
How society makes decisions about the use of stem cells.
There are many for and against arguments.
To help these arguments many authorities have been set up. These include looking at the proposals of research to see if it should be allowed. This ensures that any research involving embryos is carried out for a good reason. The licensing and monitoring centres involved in embryonic stem cell research. There are many guidelines which are involved. They also provide evidence and advice to governmental officials. There are no ethical objections to a person using multipotent stem cells derived from adults. In the UK the HFEA regulates research on human embryos.
Different genes are switched on and off. Such as the b-galactosidase which is an enzyme, it breaks down the carbohydrate lactose when it is presented in the surroundings. When lactose is not present in the environment a lactose repressor molecule binds to the DNA, this prevents the transcription of the b galactosidase gene.
Eukaryotes: genes in uncoiled, accessible regions of the eukaryote DNA can be transcribed into messenger RNA. The enzyme RNA polymerase binds to the section of DNA adjacent to the gene to be transcribed. This section is known as the promoter region. Only once the enzyme has become attached to the DNA will the transcription proceed. The gene remains switched off until the enzyme attaches to the promoter region successfully. “