Stem Cells (AQA A Level Biology)

Pluripotent & Unipotent Cells

Pluripotent embryonic stem cells

• Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta)

• Pluripotent stem cells can divide in unlimited numbers and keep replacing themselves

• They can be used in treating human disorders

Induced pluripotent stem cells (iPS cells)

• iPS cells can be produced from adult somatic cells using appropriate protein transcription factors

• These transcription factors cause specific genes to be expressed which dedifferentiate a cell back to its pluripotent state

• Each individual can have their own pluripotent stem cell line produced from their body's cells and these could potentially be used to generate transplants without the risk of immune rejection

Multipotent adult stem cells

• As tissues, organs and organ systems develop, cells become more and more specialised

• Cells must differentiate and specialise to fulfil particular roles. As a result, these adult cells gradually lose their ability to divide until eventually, they are no longer able to divide

• However, small numbers of stem cells (known as adult stem cells) remain to produce new cells for the essential processes of growth, cell replacement and tissue repair

• Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able to produce a limited range of cell types – they are multipotent

• For example, the stem cells found in bone marrow are multipotent adult stem cells – they can only differentiate into blood cells (red blood cells, monocytes, neutrophils and lymphocytes)

• In adults, stem cells can be found throughout the body (eg. in the bone marrow, skin, gut, heart and brain)

• Research is being carried out on stem cell therapy, which is the introduction of adult stem cells into damaged tissue to treat diseases (eg. leukemia) and injuries (eg. skin burns)

Unipotent cells

• Unipotent cells are adult cells that can only differentiate into their own lineage

  • For example, heart muscle cells (cardiomyocytes) can generate new cardiomyocytes through the cell cycle to build and replace heart muscle

• Most cells in animal bodies are unipotent

There are different levels of potency that cells can have. Totipotent cells have the highest potency and can therefore differentiate into any type of cell. Unipotent cells have the lowest potency, only being able to divide into one cell type.