1. 1.4 The Cell Cycle (Continued)
“More about Interphase”

2. Interesting Cell Facts
Cell Cycle – A continuous sequence of cell growth and division, including the stages of interphase, mitosis and cytokinesis.
You lose about 30,000 – 40,000 skin cells every day
If you collected all the dead cells that you shed over a day you would have about 0.5 g of dead cells.
Young people: Skin cells mature and come to surface over a 4 week period.
Elderly people: Surface cells are held in the skin up to 75 days, making them look duller in appearance

3. How do you keep your skin healthy?
Stay out of the sun
Apply creams

4. “Interphase Has Sub-Stages”
5 basic phases of a cells life; G1, S, G2, Mitosis, and cytokinesis
cell spends 90% of its life in interphase, a collection of G1, S, and G2 phases.
First Growth Phase 1 (G1) - Cell growth
Synthesis Phase (S) - DNA replication
Second Growth Phase 2 (G2)
-Preparation for mitosis

5. Cell Cycle -- 4 Phases

6. “First Growth Phase G1 Phase”
Sub-Stage #1
“First Growth Phase G1 Phase”
The first Growth phase.
During this phase a cell grows rapidly and carries out its routine functions such as producing new proteins and organelles.
Cells not dividing remain in this phase. Most muscle and nerve cells never divide so they remain in this phase. If they die they can not be replaced.
If the cell is healthy and conditions are favourable, the cell moves onto the next phase.

7. “Synthesis Phase” Sub-Stage #2
DNA is copied (synthesized) in this phase.
Key proteins for chromosomes are produced during this phase.
At the end of this phase each chromosome is now 2 chromatids attached at the centromere.

8. “Second Growth Phase G2 Phase”
Sub-Stage #3
“Second Growth Phase G2 Phase”
Shortest sub-stage in interphase.
Preparation of organelles are made for the nucleus to divide.
Microtubules, or hollow protein fibers, are assembled and will be used to move the chromosome around and eventually separate them.

9. Interphase Video
Eukaryotic Cell Cycle | Biology | Genetics

10. To Divide or Not to Divide

11. Cell Cycle Checkpoints
There are ‘checkpoints’ in a cell’s life that determine if cell will continue to divide or not
Cell division will not take place if:
1. There are not enough nutrients to support cell growth
2. The DNA has not doubled
3. The DNA is damaged

12. Cell Division
Many cells in our bodies have entered the non-dividing stage where they are no longer reproducing
ex: nerve cells, muscle cells, bone cells
Most normal cells will undergo rounds of cell division before dying
apoptosis = programmed cell death

13. Cell Death
All cells are pre-programmed to die at some point (apoptosis)
Some cells die prematurely from damages that cannot be repaired
Some other cells commit “suicide” where cells break down in an organized way if the cell is:
pre-programmed (ex: a fetus’s hands & feet)
compromised (cell division goes wrong, cell is infected with a virus, etc.)

15. Case Studies: Sickle Cell Anemia Malignant (Cancerous) Tumours
What happens when cell division goes wrong but the cell doesn’t stop dividing?
Case Studies:
Sickle Cell Anemia
Malignant (Cancerous) Tumours

16. What is a Mutation? A change in the genetic code of a cell
Happens by chance
when DNA is doubling in interphase, sometimes the order of letters gets mixed up
Can be good or bad
good = giraffes born with a longer neck reach leaves higher on a tree, animals with superior reflexes can better catch their prey
bad = tumours like cancer, disorders like Down’s syndrome or muscular dystrophy

17. Cancer & the Cell Cycle
Some cells start dividing normally, but then mutate so that they ignore the “stop dividing signs” in the cell cycle
some cancer cells have been found to produce a special protein that signals to cells that they don’t have to stop dividing
in other cancer cells, mutations don’t allow the host cell to produce or even recognize the ‘suicide’ proteins that signal normal cell death
Rapid, uncontrolled division of cells is known as a tumour

18. Name 4 lifestyle factors that could contribute to developing tumours in the lungs (and ultimately, lung cancer)