Topic 8.2 Gene expression is controlled by a number of features

Question 1

What are stem cells?

Answer 1

Undifferentiated / unspecialised cells capable of:
1. Dividing to replace themselves indefinitely
2. 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 - see 8.2.2)
● So mRNA is transcribed only from these genes and then translated to form proteins
● These proteins modify cells permanently and determine cell structure / function

Question 3

Describe totipotent cells

Answer 3

● Occur for a limited time in early mammalian embryos
● Can divide AND differentiate into any type of body cell (including extra-embryonic cells eg. placenta)

Question 4

Describe pluripotent cells

Answer 4

● Found in mammalian embryos (after first few cell divisions)
● Can divide AND differentiate into most cell types (every cell type in the body but not placental cells)

Question 5

Describe multipotent cells

Answer 5

● Found in mature mammals
● Can divide AND differentiate into a
limited number of cell types

Question 6

Describe unipotent cells, using an example

Answer 6

● Found in mature mammals
● Can divide AND differentiate into just one cell type

Question 7

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

Answer 7

● Transplanted into patients to divide in unlimited numbers
● Then differentiate into required healthy cells (to replace faulty / damaged cells)

Question 8

Explain how induced pluripotent stem (iPS) cells are produced

Answer 8

1. Obtain adult somatic (body) cells (non-pluripotent cells or fibroblasts) from patient
2. Add specific protein transcription factors associated with pluripotency to cells so they express
   genes associated with pluripotency (reprogramming)
   ○ Transcription factors attach to promoter regions of DNA, stimulating or inhibiting transcription
3. 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 could relieve human suffering by
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:
X Ethical issues with embryonic stem cells as obtaining them requires destruction of an
embryo and potential life (embryo cannot consent)
X Immune system could reject cells and immunosuppressant drugs are required
X Cells could divide out of control, leading to formation of tumours / cancer