STEM CELLS

what 3 unique characteristics do stem cells have?

1) they are undifferentiated and unspecialised

2) they can undergo extensive proliferation and are capable of self-renewal through mitosis → maintains a constant pool of stem cells

3) they can undergo differentiation in the presence of appropriate molecular signals

what are the normal functions of stem cells in a living organism?

1) self-renewal to ensure constant pool of stem cells

2) growth and development

3) differentiate into specialised cells to replace cells that are lost due to cell death and injury

what is the purpose of stem cells differentiating?

to replace damaged cells or cells lost through death

what 2 types of cell division can a stem cell undergo and what are its purposes?

1) symmetrical division → stem cell divides to produce 2 genetically identical daughter stem cells. this maintains the pool of stem cells for further division.

2) asymmetrical division → stem cell divides to produce 1 genetically identical daughter stem cell and 1 progenitor daughter cell. progenitor daughter cell helps increase or renew population of specialised cells in specific tissue.

what happens if a stem cell division resulted in 2 progenitor cells all the time?

there will no longer be self-renewal and all stem cells will eventually be depleted.

Suggest how stem cells are able to differentiate into specialised cells upon receiving molecular signals.

Molecular signals may activate or shut down expression of specific genes that result in synthesis of tissue-specific structure that enable these specialised cells to perform certain functions.

What is the difference between genome of stem cell and specialised cell? What accounts for the difference in characteristics?

Their genomes are identical. The differences in gene expression cause differences in characteristics.

note: in general, as cell potency level decreases, more and more genes that allow a cell to be in a higher potency level are “switched off”.

simultaneously, more tissue-specific genes are “switched on” as specialisation increases

define totipotent stem cell, with an in-syllabus example of cell and where it’s derived from

→ totipotent stem cells have the ability to differentiate into all the cell types that are up an entire organism, including extra-embryonic tissue such as placenta.

→ tldr totipotent stem cells have the ability to give rise to an entire organism

→ eg: zygotic stem cells derived from zygote, as well as embryos produced within first 3 mitosis divisions / up to 8 cell stage

note: totipotent stem cells can also be called pluripotent and multipotent

define pluripotent stem cell, with an in-syllabus example of cell and where it’s derived from

→ pluripotent stem cells have the ability to differentiate into all the cell types that make up an organism except for extra-embryonic tissue such as the placenta

→ tldr pluripotent stem cells alone cannot form the entire organism as placenta is required for foetal nourishment and development

→ eg: embryonic stem cells (ESCs) are derived from cells of inner cell mass of blastocyst

define multipotent stem cell, with an in-syllabus example of cell and where it’s derived from

→ multipotent stem cells have the ability to differentiate into several related specialised cell types, but far fewer types than the pluripotent embryonic stem cells

→ adult stem cells, from different tissues of an organism after embryonic development. eg myeloid and lymphoid stem cells derived from bone marrow.

what is the purpose of of multipotent stem cells in the human body?

→ produce specialised cells for growth and development

→ replacement of cells that are lost due to cell death and injury

are adult stem cells found only in adults? and what is the potency of umbilical cord stem cells?

no, infants have them too. multipotent.

what are the 2 approaches to stem cell therapies and what they roughly entail?

1) stem cell transplant: adult stem cells obtained from donor, transplanted to patients

2) genetically modified stem cell transplant: removing stem cells from patient, genetically modifying them by inserting normal functional allele, reintroducing the modified stem cells into patient

list advantages and disadvantages of using stem cell transplant approach.

advantages

• no need for repeated treatment as stem cells from donor can undergo self renewal

• stem cells relatively accessible and easily obtained from donor → less ethical issues than usage of embryonic stem cells

disadvantages

• stem cells obtained from adult donor produce limited number of cell types → cannot used to be treat all diseases

• adult stem cells are found in small numbers, can be difficult to isolate and culture

• possible immune rejection or no matching donor

list advantages and disadvantages of using genetically modified stem cell transplant approach.

advantages

• no immune rejection → stem cells are the patient’s own

• less ethical issues than usage of embryonic stem cells

• no need for repeated treatment → adult stem cells capable of self-renewal, maintaining constant pool

disadvantages

• adult stem cells are found in small numbers, difficult to isolate and culture

• adult stem cells produce a limited number of cell types (multipotent) → cannot be used to treat all diseases

• risks involved in retroviruses

  • retroviral insertional mutagenesis → retrovirus integration into the genome can transform cells by oncogene activation or tumour suppressor gene inactivation → can trigger onset of cancer

why are retroviruses used as vectors for gene therapy?

retroviruses have integrase to integrate normal, functional allele into genome of target cell, hence is useful for genetically modified stem cell transplants

compare the use of embryonic stem cells and adult stem cells in stem cell therapy and research

what are the principles of bioethics?

1) respect for persons → inherent worth and autonomy of each person, with informed consent

2) maximising benefits, minimising harms → how one would directly help others and act in their best interests while “doing no harm”.

3) justice → treat people fairly and equitably, sharing resources, risks, and core

what are the arguments against using embryonic stem cells?

what are the arguments for using embryonic stem cells?

describe what iPSCs are.

induced pluripotent stem cells are differentiated and specialised adult somatic cells → reprogrammed to become pluripotent stem cells, by losing specialist functions and behaving virtually in the same way as embryonic stem cells.

list the advantages of using iPSCs.

list the disadvantages/risks of using iPSCs.