Stem Cells
Biology: Cambridge International A Level, topic 5.1.5
Stem Cells
Stem cells are unspecialised cells. Unspecialised cells are capable of dividing and differentiating into any type of cell. Stem cells divide by mitosis and are important in tissue repair.
Totipotent cells
- Totipotent cells exist for only a very limited time during embryonic development in mammals (the first few cell divisions).
- During development, totipotent cells translate only part of their DNA. This means that the cells remain unspecialised.
- Totipotent cells are able to produce any type of body cell, as well as cells of supportive structures such as the placenta.
- They are the most unspecialised stem cell.
Pluripotent cells
- Totipotent cells develop into pluripotent cells in embryos.
- Pluripotent cells are able to divide in unlimited numbers and produce any type of cell that makes up the body.
- Pluripotent cells can be used to treat human disorders.
Multipotent cells
- Multipotent cells are found in mature mammals.
- Multipotent cells can develop into a limited number of cell types.
- E.g. Multipotent cells in the bone marrow can produce a range of blood cells.
Unipotent cells
- Unipotent cells are found in mature mammals.
- Unipotent cells can divide to produce new cells but can only produce one type of cell.
- E.g. Cardiomyocytes are unipotent cells that can produce new muscle cells.
Specialisation of Stem Cells
Stem cells become specialised during embryonic development. Specialised cells only express some of the genes in their DNA.
Totipotent cells
- Totipotent cells become specialised during embryonic development.
- When the cells become specialised, only some genes in the cell are activated.
- Only the activated genes are expressed.
Proteins in differentiation
- If a gene is expressed, it is transcribed into mRNA and translated into a protein.
- Differentiation happens as certain proteins are made.
- The presence of certain proteins means a cell has become specialised.
Test yourself on Stem Cells
What is the most unspecialised stem cell?
Which of the following statements about stem cells are true?
Stages in Specialisation of Stem Cells
When do totipotent cells become specialised?
Which of the following statements about cell specialisation are true?