• Muscle cells, bone cells, brain cells, skin cells, etc.

• All these cells have the same DNA! The reason they appear different and have different function is because they express different set of genes (this process is termed as differentiation)

  • Note that the only cell type that is genetically different from the rest of the other cells are the gametes, as they are formed via meiosis (haploid and have different allele combinations)

1. Self-renew means that the stem cell are capable divide and give rise to more of themselves (stem cells).

   • this is achieved via mitosis.

   • stem cells can do this repeatedly, described by term 'extensive proliferation'. 

2. Differentiating means that when dividing the stem cell are able to differentiate (become) into a specialised cell (e.g., muscle cell / blood cell)

   • this is achieved through the changes in gene expression via molecular signalling. (refer above on Cell differentiation video!)

3. A differentiated cell has a specialised function, e.g., muscle cells can contract. Which means an undifferenitated cell does not have any tissue-specific function.

1. Having the highest potential means that the stem cell can differentiate into all possible cell types. While having the lowest potential means that the stem cell can only differentiate into one possible cell type.

   • Consider the analogy of a ball at the top of the hill (see Fig. A).

     • At the top of the hill, it has the highest potential, as it can roll into any of the 4 possible point at the bottom of the hill.

     • However, as it starts to roll down (differentiating), some of the paths no longer leads to all possible points, this decreases its potential.

     • This idea is similar to that of a stem cell, it starts out with the highest potential of becoming any cell, but as it gradually differentiates, its potency decreases, until it eventually becomes a specialised cell type. 

2. Totipotent > Pluripotent > Multipotent > Unipotent (note that unipotent is not required in the syllabus)

   • Consider the following acronym to help you remember the potency in order:

     • The (Toti) - or you can remember that Toti refers to total, so ALL possible cell type

     • Pie (Pluri) - letter P is closer to letter T, so it is the next highest in potential

     • Maker (Multi)

3. Totipotent - all specialised cell types

   • this means that a single totipotent stem cell can form an entire organism on its own.

Pluripotent - all specialised cell types except for extraembryonic cells

• 'extra' refers to outside, so pluripotent stem cells cannot form cells that are outside of the embyro, this includes the placenta and umbilical cord (see Fig. B).

Multipotent - only specialised cells within a closely related family (e.g., all blood cells)