1. (1) Division and differentiation in human cells
(F) Cancer Cells
(A) Somatic cells
Human Cells
(E) Uses of stem cells
(B) Differentiation in cells
(D) Germline cells
(C) Stem cells

2. Division and differentiation in human cells (B)
Define what is meant by ‘cell differentiation’
Define what is meant by ‘selective gene expression’
Describe the difference in gene expression between an undifferentiated and differentiated cell.

3. BUT… we all started off from ONE fertilised egg!
You have learnt that there are different types of cells in your body:
BUT… we all started off from ONE fertilised egg!
How did the variations in cells arise?
What is this process called?

4. It’s all to do with your DNA and a process called cell differentiation

5. Every cell contains DNA (genes)
DNA (genes) carries the code to make a variety of different proteins
e.g. Hair, nails, antibodies, hormones

6. Cell Differentiation
Differentiation is the process by which an unspecialised cell becomes altered and adapted to perform a specialised function as part of a permanent tissue.
Once a cell becomes differentiated it only expresses the genes that code for the proteins characteristic for that type of cell.

7. Now let’s look at ONE of these cells...
Early embryo
(blastocyst)
Fertilised egg cell
Repeated mitosis and cell division
Now let’s look at ONE of these cells...
Inside the nucleus of ONE cell, there are ALL the genes…
But this cell is destined to become a blood cell, so it only switches on the genes, it NEEDS to the job of a blood cell
And switches off the genes that are not necessary.

8. Genes switched on in ALL cells Genes switched on in SOME cells
Genes that code for vital metabolites necessary for basic life processes
Genes that are only switched on in certain differentiated cells.
e.g.
insulin made by pancreas cells
antibody production
Production of digestive enzymes
Production of keratin
e.g.
enzymes needed for aerobic respiration
proteins in plasma membrane
Proteins needed to make cell organelles

9. Selective gene expression

10. Selective gene expression
Every cell contains DNA.
Short sections of DNA which have a specific job are called genes.
Genes carry the code to make a variety of different proteins.
Not all proteins are needed at the same time.
Therefore, the genes that control the production of proteins can be switched on or off.
This prevents resources (energy) being wasted.

11. Selective gene expression

12. Back to differentiation…
Fully grown adult
Early embryo
(blastocyst)
Fertilised egg cell
Growth and DIFFERENTIATION
Repeated mitosis and cell division
(see figure 1.1 on page 2 for more details!)

13. Back to differentiation & Selective gene expression
(see figure 1.4 on page 4)