Stem Cells

Question 1

What are stem cells?

Answer 1

Undifferentiated / unspecialised cells capable of: Dividing by mitosis to replace themselves and capable of differentiating into other types of specialised cells

Question 2

Describe how stem cells become specialised during development

Answer 2

Stimuli lead to activation of some genes due to transcription factors, so mRNA is transcribed only from these genes and then translated to form proteins. These proteins modify cells permanently and determine cell structure and function

Question 3

Describe totipotent cells

Answer 3

They occur for a limited time in early mammalian embryos. They can divide and differentiate into any type of body cell.

Question 4

Describe pluripotent cells

Answer 4

Found in mammalian embryos after the first few cell divisions. They can divide and differentiate into most cell types.

Question 5

Describe multipotent cells

Answer 5

They are found in mature mammals. They can divide and differentiate into a limited number of cell types.

Question 6

Describe unipotent cells, using an example

Answer 6

They are found in mature mammals and can divide and differentiate into just one cell type. For example, unipotent cells in the heart can divide and differentiate into cardiomyocytes (cardiac muscle cells)

Question 7

Explain how stem cells can be used in the treatment of human disorders

Answer 7

They can be transplanted into patients to divide and then differentiate into required healthy cells (to replace faulty / damaged cells)

Question 8

Explain how induced pluripotent stem (iPS) cells are produced

Answer 8

• Obtain adult somatic (body) cells (non-pluripotent cells) from patient
• Add specific protein transcription factors associated with pluripotency to cells so they express genes associated with pluripotency
• Transcription factors attach to promoter regions of DNA, stimulating or inhibiting transcription
• Culture cells to allow them to divide by mitosis

Question 9

Evaluate the use of stem cells in treating human disorders

Answer 9

For:
* Can divide and differentiate into required healthy cells, so can treat illnesses, saving lives and improving quality of life
* Embryos are often left over from IVF and so would otherwise be destroyed
* iPS cells unlikely to be rejected by patient’s immune system as made with patient’s own cells
* iPS cells can be made without destruction of embryo and adult can give permission

Against:
* Ethical issues with embryonic stem cells as obtaining them requires destruction of an
embryo and potential life (embryo cannot consent)
* Immune system could reject cells and immunosuppressant drugs are required
* Cells could divide out of control, leading to formation of tumours / cancer