6.5 Stem Cells

Question 1

What are stem cells?

Answer 1

Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism.

Question 2

What is meant by ‘undifferentiated’?

Answer 2

Stem cells that are not adapted to any function (unspecialised).

Question 3

What problems can the division of stem cells cause?

Answer 3

If stem cells divide too quickly:
- Tissues are not efficiently replaced
- Leads to ageing
If stem cells divide too quickly:
- Masses of cells formed (tumours)
- Leads to cancer development.

Question 4

What is meant by potency?

Answer 4

A cell’s ability to differentiate into different cell types.
Totipotent/pluripotent/multipotent

Question 5

What is meant by totipotent?

Answer 5

• Can differentiate into any type of cell
• e.g. zygotes, 8/16 cells from first few mitotic divisions
• Can also differentiate into extra-embryonic tissues, e.g. amnion, umbilicus.

Question 6

What is meant by pluripotent?

Answer 6

• Can form all tissue types, but not whole organisms.
• Present in early embryos as origin of different types of tissue.

Question 7

What is meant by multipotent?

Answer 7

• Can only form a range of cells within a certain type of tissue.
  E.g. haematological stem cells give rise to various types of blood cell.

Question 8

What is the benefit of being a multicellular organism?

Answer 8

They are more efficient:
- Groups of cells with different functions working together as one unit can make use of resources more efficiently

Question 9

How do blood cells exemplify the benefits of being a multicellular organism?

Answer 9

• Erythrocytes and neutrophils both present in blood
• They have differentiated to become more efficient at their particular functions.

Question 10

Why do blood cells need to be produced from stem cells?

Answer 10

• Erythrocytes and neutrophils have different structures and functions
• They have to differentiate to carry out their function

Question 11

Where are the stem cells for blood cells found?

Answer 11

Bone marrow

Question 12

How long do neutrophils live?

Answer 12

~6 hrs

Question 13

How many neutrophils are produced by stem cells per hour?

Answer 13

~1.6 billion per kg per hour - increases during infection.

Question 14

What are the two main sources of animal stem cells?

Answer 14

• Embryonic stem cells
• Tissue (adult) stem cells

Question 15

What are embryonic stem cells? - where present, potency?

Answer 15

• Present at early stage of embryo development
• Totipotent
• After a blastocyst (mass of cells) forms, cells are in a pluripotent state until birth

Question 16

What are tissue (adult) stem cells? - purpose, potency, recovery methods?

Answer 16

• Present throughout life from birth
• Found in specific areas, e.g. bone marrow
• Multipotent - Although growing evidence that they can be artificially triggered to become pluripotent
• Can also be harvested from umbilical cords

Question 17

Where are stem cells found in plants?

Answer 17

• Present in meristematic tissue
• Found wherever growth occurs, e.g. tips of roots and shoots (termed apical meristems)
• Also found in vascular cambium (sandwiched between xylem & phloem) - Cells differentiate into xylem + phloem
  => Vascular tissue grows as plant grows

Question 18

What potency are plant stem cells at?

Answer 18

Meristematic stem cells are pluripotent throughout the life of the plant.

Question 19

Name some of the potential uses of stem cells.

Answer 19

Heart disease, type 1 diabetes, Parkinson’s disease, macular degeneration, birth defects, spinal injuries

Question 20

How are stem cells used already?

Answer 20

Treatment of burns - Stem cells grown on biodegradable meshes produce new skin: quicker than taking graft from other part of body

Drug trials - Potential new drugs tested on stem cell cultures before animals/humans

Developmental biology - can divide indefinitely and differentiate into almost any cell .˙. Useful in studying changes as multicellular organisms grow and develop from a single cell

Question 21

What are the main objections to using stem cells?

Answer 21

• Removal of stem cells from embryos usually results in their destruction
• Religious objections to use of embryos
• Moral objections - many people believe that life starts at conception .˙. Extraction of stem cells is murder

Question 22

What is Alzheimer’s disease and how might stem cells be used to treat it?

Answer 22

• Nerve cells in the brain die in increasing numbers
• Results in severe memory loss
• Stem cells may be used to regrow healthy nerve cells.

Question 23

What is Parkinson’s disease and how might stem cells be used to treat it?

Answer 23

• Patients suffer from uncontrollable tremors
• Dopamine-releasing nerve cells in the brain are lost, which are needed to control movement
• Transplanted stem cells may help to regenerate dopamine-producing cells.

Question 24

What are the advantages of harvesting tissue stem cells from umbilical cords?

Answer 24

• Plentiful supply of umbilical cords
• Non-invasive
• Can be stored easily
• Would not be rejected in cultured tissue transplant (to umbilicus’ owner)

Question 25

What are some solutions for the opposition to the use of animal stem cells?

Answer 25

• Umbilical stem cells - Although their use overcomes issues to a large extent, they are multipotent (not pluripotent) - uses restricted
• Tissue stem cells could be used, however they do not divide as well, + more likely to mutate

Developments being made:
- iSPCs (induced pluripotent stem cells) - genetically modified to act as embryonic stem cells .˙. Pluripotent stem cells