Unit 7- Stem Cells

Question 1

What is the potency and source of totipotent stem cells?

Answer 1

• found in zygote/very early embryo (8 cell divisions)

- are able to produce any type of cell including extra embryonic membranes to form more embryo

Question 2

What is the potency and source of pluripotent stem cells?

Answer 2

• found in blastocyst inner cell mass

- can produce any cell type except extra embryonic membrane, so can’t form a new embryo

Question 3

What is the potency and source of multipotent stem cells?

Answer 3

• found in most adult tissue

- can produce a limited range of related cell types

Question 4

What is happening to cells when they change from totipotent to pluripotent etc

Answer 4

Epigenetic changes to cells switch off particular genes for cell types reducing the potency

Question 5

Give an example of a multipotent stem cell, and what is can differentiate into

Answer 5

Bone marrow cells

- may form red blood cells, white blood cells and platelets

Question 6

How can we get hold of embryo stem cells?

Answer 6

• in IVF, embryos are created and inserted into the mother

- there are inevitably spare embryos which contain pluripotent stem cells

Question 7

What are the advantages and disadvantages of extracting pluripotent stem cells from embryos?

Answer 7

+ ability to produce almost all types of cells, potential to grown replacement organs and tissues
+ provision of cells for drug testing can replace the need for animal testing
- possible rejection of cells by immune system as the cells aren’t from then patient
- ethical issues of killing an embryo

Question 8

What are the ethical views for and against using embryonic stem cells donated from fertility centres?

Answer 8

• some religions consider human life and rights to start at conception
• embryos cannot give consent
• killing an embryo is no different from killing a person
  + potential benefits outweigh harm
  + banking cell embryos now will reduce future need for them

Question 9

Where are adult stem cells obtained, and what potency are they?

Answer 9

• most body tissues contain a small number of adult stem cells
• these are multipotent

Question 10

Issues and benefits of adult stem cells

Answer 10

• stem cells won’t get rejected of they are from the patient
• difficult to find and culture for transfer
• not all cell types have adult stem cells
• in bone marrow transplants the implanted white blood cells may damage the recipient

Question 11

Describe how cells can become induced pluripotent stem cells

Answer 11

• genes are inserted into fibroblasts using retroviruses
• the genes code for transcription factors which reprogrammed the fibroblast to undo changes made in cell specialisation to become pluripotent stem cells

Question 12

What kind of cells can be reprogrammed into IPS cells? And what are they?

Answer 12

Fibroblasts

- cells found in skin and other tissues

Question 13

What are the issues of using IPS cells?

Answer 13

• the genes used can promote cancer development

- sometimes the cells are changed in a way that still causes rejection by own immune system

Question 14

How does use of IPS cells avoid ethical issues?

Answer 14

No killing of embryos

Question 15

Identical twins develop when a single embryo splits into 2 in early development. Explain the observation that a split in the first few hours results in each embryo having its own placenta but a split after reaching the uterus results in embryos sharing a placenta

Answer 15

• early embryos have totipotent cells, which can form a placenta in each new embryo
• cells are pluripotent by the time they reach the uterus because of epigenetic changes
• both embryos in a later split depend on cells that can’t differentiate into more placental tissue as they are no longer totipotent, therefore they share the placenta they already have