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Define what a stem cell is
Stem cells are unspecialised cells that can develop into other types of cell
Some children with SCID have been treated with stem cells. Stem cells can divide and develop into any type of blood cell, including white blood cells. The treatment used with the children is described in the diagram.Using the information given, suggest and explain three reasons why stem cells were used in this treatment.
They can divide to form new blood cells so can replace existing faulty cells.
They can form any type of white blood cell;
so restores ability to fight infections.
Child's own cells used so little risk of rejection.
Give 2 examples of totipotent cells
Cells in the early embyro up to 5 days
The other viral enzyme is called integrase. Integrase inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell's genes. Some of the children in the trial developed cancer. How might the insertion of the DNA have caused cancer?
Affects tumour suppressor gene. Inactivates tumour suppressor gene. Rate of cell division increase allowing tumour cells to continue to divide.
The other viral enzyme is called integrase. Integrase inserts the DNA copy anywhere in the DNA of the host cell. It may even insert the DNA copy in one of the host cell's genes. Five out of the 20 children in the trial developed cancer. Although the cancer was treated successfully, the doctors decided to stop the trial in its early stages. They then reviewed the situation and decided to continue. Do you agree with their decision to continue? Explain your answer
Yes because SCID patients unlikely to survive and it only affects 25%/ of children.No because risk of developing cancer is (high) 25%.Cancer may recur. Only short time scale so more may develop cancer
Give two characteristic features of stem cells.
They will replace themselves (keep dividing). They can differentiate into other cells e.g. multipotent cells.
Where do pluripotent cells come from?
After 5 days totipotent cells begin to differentiate, forming a hollow ball of cells called a blastocyst. The blastocyst has an outer layer of cells which for the placenta and a cluster of cells inside the hollow sphere called the inner cell mass. It is these cells that are pluripotent.
Whats the difference between totipotent and pluripotent stem cells?
Totipotent stem cells can mature into any type of body cell and so are capable of giving rise to a whole organism. Pluripotent cells have the potential to create every type of body cell but not the cells of the placenta and the umbilical cord. Pluripotent cells are therefore incapable of making a whole organisms
For the past 20 years stem cells have been used to grow new skin to treat victim burns by taking skin from undamaged areas of the patients body where epidermal stem cell produce skin cells in sheets. Give 2 limitations to this technique
Stem cells do not give rise to the more complex skin structures such as receptors and hair follicles.
The time taken to produce large areas of skin.
Name the 4 types of stem cells
Totipotent, pluripotent, multipotent, unipotent
Human adult stem cells
Are only found in specific tissue such as bone marrow and the brain found in an adult.
State the main difference between adult stem cells and embryonic stem cells.
Adult stem cells are multipotent whilst embryonic stem cells are pluripotent
Why do scientists prefer to use embryonic stems cells rather than adult stem cells
Adult stem cells are, difficult to isolate, more difficult to grow in a tissue culture and only give rise to limited number of body tissues
Only embryonic stem cells are natrually pluripotenet
How many protein transcription factors are required to turn specialised adult cells into stem cells
What are the limitations of using adult stem cells (multipotent)
Multipotent cells from a specific patient may take time to develop in culture before they produce an adequate amount for treatment
Adult stem cells may contain damaged DNA due to ageinig toxins and random DNA mutations during replication
Human embryonic stem cells
These stem cells exist in all human embyos
State the 3 general properties of stem cells
They can divide and renew themselves over long periods
They are unspecialised (Undifferentiated)
They can develop into other specialised cell types
Where can stem cells be found?
Stem cells are found in the embryo and in some adult tissue
Explain the characteristics of totipotent stem cells and the sources of it.
Totipotent cells are cells that can mature into any type of body cell in an organism including the cells that make up the placenta in mammals. Totipotent cells are only present in mammals in the first few cell divisions of an embryo.
Explain the characteristics of unipotent stem cells and the sources of it.
Unipotent stem cells can only differentiate into one type of cell
Explain the characteristics of pluripotent stem cells and the sources of it.
Stem cells that can specialise into any cell in the body but don't have the ability to become the cells that make up the placenta
Explain the characteristics of multipotent stem cells and the sources of it.
Multipotent stem cells are able to differentiate into a few different types of cell. For example multipotent stem cells found in the bone marrow can form red and white blood cells.
State the benefits of using stem cells in medicine
Saves many lives and improves the quality of people's lives.
If IPS could be made from a patient's own cells, what could be the benefit of this?
The cells could be used to grow new tissue or an organ and since the cells are from the patient the tissue or organ won't be rejected by the patient's body as the cells are genetically identical to the patients cells.
The ability to differentiate into specialised cells
Why are some people for embryonic stem cell research
They argue that these embryos are the unwanted byproducts of IVF treatment, which the parents willingly donated
The use of embryos involves no suffering
The ability to replicate indefinitely
What are the 2 main advantages that IPS has over embryonic stem cells
They don't require the destruction of an embryo which for some is an ethical dilemma.
They can be made from the patients own cells so are unlikely to be rejected by their immune system.
Explain why induced pluripotent cells are of interest.
They are of interest because whilst they have the potential to be as flexible as embryonic stem cells, they are obtained from adult tissue so they won't result in the destruction of embryos hence why they don't raise as many ethical issues as embryonic stem cells
Describe the production of specialised cells from totipotent cells
Under the right conditions, some genes are expressed and others are switched off
mRNA is only transcribed from specific genes and the mRNA from these genes is then translated to proteins
The proteins modify the cell by determining the cell structure and controlling the processes in the cell
It is the changes in the cell by these proteins that cause the cell to become specialsed
Do all parts of the totipotent cell DNA need to be transcribed and translated to from specialised cells?
No. The production of specialised cells from totipotent cells requires only part of the cell's DNA to be translated.
Why does stem cells become specialised?
Stem cells become specialised because during their development they only transcribe and translate part of their DNA
Pluripotent cells and their use in treating human disorders.
Some stem cells can be used to replace cells damaged by injury or illness. For example Bone marrow transplants can be used to replace the faulty bone marrow in patients that produce healthy blood cells. This technique has been used to treat leukaemia and lymphoma
Gone marrow transplants can be used to replace the faulty bone marrow in patients that produce healthy blood cells. This technique has been used to treat many diseases and gentic disorders. Name 4
Leukaemia, lymphoma, sickle-cell anaemia, SCID
What are cardiomyocytes?
Heart muscle cells that make up a lot of the tissue in our hearts
Unipotent cells exemplified by cardiomyocytes.
Some scientists believe that old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart
What are IPS
Induced pluripotent stem cells are stems cells made from somatic cells which have already differentiated
How were IPS cell developed?
The scientists who discovered it found that there were four genes expressed in a mouse embryo that control pluripotency. They then added these four genes to somatic cells and found that the transcription factor produced by these genes made the cell pluripotent
Evaluate the ethical objections around pluripotent embryonic stem cells.
As the procedure results in the destruction of an embryo that could have become a fetus if placed in a womb, some people who believe in life at fertilisation say that it is wrong to take away that individuals right to life
How do plant and animal cells differ in relation to differentiation?
Why is only a small proportion of the cell's DNA translated when it specialises?
Stem cells are found in human bone marrow and in embryos. These cells can divide to form
a clone. Stem cells are able to develop into different types of cell.Use your knowledge of genes to explain how stem cells are able to develop into different types of cell.
different genes expressed (switched on) so different proteins produced.
What is a clone?
Bone marrow transplants used in treating diseases such as leukaemia involve the transfer of stem cells from a genetically matched donor. The injection of stem cells into specific organs of the body has been used to treat other diseases. These stem cells develop into similar tissues as their surroundings. Suggest one way in which the development of these cells is influenced by their surroundings.
Growth hormones released by surrounding cells.
Bone marrow transplants used in treating diseases such as leukaemia involve the transfer of stem cells from a genetically matched donor. Suggest why the stem cells are obtained from a genetically matched donor.
To prevent rejection ( from an immune response)
Plant physiologists attempted to produce papaya plants using tissue culture. They investigated the effects of different concentrations of two plant growth factors on
small pieces of the stem tip from a papaya plant. Their results are shown in the table. Callus is a mass of undifferentiated plant cells. Plantlets are small plants. Explain the evidence from the table that cells from the stem tip are totipotent.
Gives rise to new plants so must be able to develop into different tissues and other
specialised cell types.
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