Stem Cells

Question 1

describe the features of stem cells

Answer 1

• unspecialised/undifferentiated
• capable of dividing and renewing themselves for long periods via mitotic cell division (self-renewing), while still maintaining the undifferentiated state
• can form progenitor cells which differentiate into specialised cell types under the presence of appropriate chemical signals

Question 2

why do stem cells undergo asymmetrical division?

Answer 2

stem cell divides to produce:
* one daughter cell that is identical to the parental stem cell, ensuring a constant pool of stem cells
* one progenitor cell that is only capable of differentiating into related specialised cell type, increasing/renewing the population of specialised cells in a specific tissue

Question 3

why do stem cells undergo symmetrical division?

Answer 3

• stem cell divides to produce two daughter stem cells that possess the same characteristics as parental cell (same developmental and differentiation potential)
• enlarges population of undifferentiated cells and increases the pool of stem cells for further division

Question 4

describe the characteristics of totipotent stem cells

Answer 4

• have the potential to become any cell type to form an entire organism, including the extra-embryonic membranes (e.g. placental membranes surrounding the embryo)
• zygote and the first 16 cells produced by mitotic division of the zygote are totipotent

Question 5

describe the characteristics of pluripotent stem cells

Answer 5

• have the ability to form progenitor cells which can differentiate into almost any cell type to form any organ. they can form any cell type but not those of the extra-embryonic membranes
• embryonic stem cells (ES cells) from the inner cell mass of the blastocyst are pluripotent
• ES cells can give rise to cells that differentiate into any of the three germ layers: mesoderm (muscle), ectoderm (epidermal tissues) and endoderm (lungs)

Question 6

describe the characteristics of multipotent stem cells

Answer 6

• have the potential to become a limited range of cell types in the adult body
• serve to replace cells lost through wear and tear
• also known as adult stem cells (lymphoid and myeloid stem cells formed from hematopoietic/blood stem cells, able to differentiate into various types of blood cells)

Question 7

discuss the uses of stem cells in research and medical applications (4 pts)

Answer 7

• stem cell research has enabled scientists to better identify the genes and proteins critical to cell division and differentiation, leading to new and better treatments for certain medical conditions resulting from errors in cell division and differentiation
• stem cells can be differentiated into specific cells/tissues which can be used to test for the efficacy and safety of drugs
• stem cells can be used to generate replacement of cells, tissues or organs for transplant
• cells and tissues generated are immunologically compatible with the person from whom the adult stem cells are harvested, enabling organ transplant to be carried out without fear of rejection during the transplant process

Question 8

discuss the ethical issues of the use of stem cells

Answer 8

• oocytes could be used to create ES cell by transferring nuclear DNA from a somatic cell
• harvesting oocytes is painful to the donor
• neglecting the welfare of donors of oocyte, increasing risk of exploitation for research and commercial benefits
• could cause serious health problems during oocyte retrieval from donor
• e.g. reducing quality/number of remaining oocytes for future reproductive purposes
• researchers may not have ensured the confidentiality of the donor and such information may subject the donor to possible exploitation
• researchers might not have obtained informed consent of donors of oocytes in which the donors fully understand the implications of the donation
• harvesting ES cells from an embryo requires the destruction of an embryo, which has the potential to develop into a full-sized organism
• intentional creation of embryos for research and destroying them in the process is considered as active killing and violates respect for nascent human life
• patients may not have provided informed consent as they do not fully understand the implications arising from the medical application of ES cells
• implantation of human stem cells into other animals will result in the development of human part on these other animals which is unnatural and poses some moral issues
• application of stem cells as part of a medical therapy can have medical risks e.g. immunological incompatibility
• application of stem cells as part of a medical therapy may not achieve the intended benefits of the treatment (may not have been sufficient successful trials to support the benefits claimed/patient may not have a good chance of being cured due to poor health)
• only the rich has access to and can afford the stem cell therapies that come with high costs

Question 9

discuss how human induced pluripotent stem cells (iPSCs) overcome ethical implications of the application of stem cells in research and medical applications

Answer 9

• iPSCs are created when specialised adult cells are genetically reprogrammed to assume a stem cell-like state
• these have similar features to embryonic stem cells, eliminating the need to harvest and use embryonic stem cells
• iPSCs also eliminate the risk of exploitation of women for donation of embryos