Stem cells

what is a stem cell

undifferentiated cells that can differentiate into any cell type by mitosis

What are the two key features of stem cells?

• Self-renewal – can divide repeatedly by mitosis.

• Potency – ability to differentiate into specialised cell types.

What is differentiation?

• The process by which a stem cell becomes a specialised cell.

• Occurs through changes in gene expression (some genes switched on/off).

What is meant by potency?

• Potency is the range of different cell types a stem cell can differentiate into.

• Potency decreases as cells become more specialised.

What are the three types of stem cell potency?

• Totipotent

• Pluripotent

• Multipotent

What are totipotent stem cells?

• Can differentiate into any cell type, including extra-embryonic cells (e.g. placenta).

• Found in:

  • the zygote, and

  • embryos up to the 16-cell stage.

morula

very early stage embryo

What are pluripotent stem cells?

• Can differentiate into any cell type in the embryo,

• Cannot form extra-embryonic cells (placenta).

• Found in early embryos (embryonic stem cells).

What are multipotent stem cells?

• Can differentiate into a limited range of related cell types.

• Less potent than embryonic stem cells.

• Found in adult tissues.

What are adult stem cells?

• Stem cells that remain in adult tissues.

• Are multipotent.

• Used for growth, cell replacement and tissue repair.

Why are bone marrow stem cells multipotent?

They can differentiate into blood cells only, such as:

• red blood cells

• neutrophils

• monocytes

• lymphocytes

Where are adult stem cells found?

• Bone marrow

• Skin

• Gut lining

• Brain

• Heart

Why do most adult cells lose the ability to divide?

• As cells differentiate, they become specialised.

• Many lose the ability to undergo mitosis permanently.

What is stem cell therapy?

• The use of stem cells to replace or repair damaged tissues.

• Typically uses adult (multipotent) stem cells.

Give examples of stem cell therapy applications.

• Treating leukaemia (bone marrow transplants).

• Repairing skin burns.

• Research into treating degenerative diseases.

How does potency change during development?

• Totipotent → pluripotent → multipotent

• Potency decreases as cells become more specialised.

unipotent differentiated cells are in the —— phase of the cell cycle

G0

what are the advantages of stem cells?

• Can replace damaged or diseased cells, e.g. in leukaemia or skin burns

• Stem cells can divide repeatedly, providing a long-term supply of new cells

• Pluripotent stem cells can form many different cell types

• May reduce the need for organ transplants

• Useful for medical research and understanding disease development

• improved quality of life

what are disadvantages of stem cells

• Ethical concerns over the use of embryonic stem cells (destruction of embryos)

• Risk of tumour formation if cell division is not controlled

• Immune rejection may occur if donor cells are used

• Adult stem cells are multipotent, so can only form a limited range of cells

• Stem cell treatments are often expensive and still experimental