1. Cell Cycle Regulation and Cancer
Lecture #15
Honors Biology
Ms. Day

2. Another Type of Cell Division: Binary Fission
Prokaryotes (bacteria)
Reproduce by a type of cell division called binary fission
No nucleus  no karyokinesis!!

3. The bacterial chromosome replicates
In binary fission,
The bacterial chromosome replicates
The two daughter chromosomes move apart
Origin of
replication
E. coli cell
Bacterial
Chromosome
Cell wall
Plasma
Membrane
Two copies
of origin
Origin
Chromosome replication begins.
Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1
Replication continues. One copy of the origin is now at each end of the cell. 2
Replication finishes. The plasma membrane grows inward, and
new cell wall is deposited. 3
Figure 12.11
Two daughter cells result. 4

5. Cell Cycle needs to be controlled (Regulated)
The cell cycle has 3 checkpoints
A place where stop and go signals can regulate (control) cycle
Signals make sure things
been completed
completed correctly
There are 3 checkpoints
G1 checkpoint
G2 Checkpoint
M checkpoint

6. The Cell Cycle Control System
Figure 12.14
Control system
G2 checkpoint
M checkpoint
G1 checkpoint G1 S G2 M

7. Checkpoint = give “go” or “stop” signals
G1 checkpoint G1 G0
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in cell cycle.
If a cell does not receive a go-ahead signal at the G1checkpoint, cell exits the cell cycle and goes into G0, a nondividing state.
Figure A, B

8. Chromosomes are lined up in the middle properly
of replicated DNA
of unreplicated (original) DNA

9. What controls the checkpoints?
Two types of proteins in cytoplasm
Cyclins
cyclin-dependent kinases (Cdks)

10. CYCLIN DEPENDENT KINASE (CDK)
INACTIVE FORM
CYCLIN DEPENDENT KINASE (CDK)
CYCLIN +
ACTIVE FORM
CDK/CYCLIN COMPLEX

11. Active vs. Inactive??
What happens when cyclins and cdks are in the ACTIVE form?
Cells can pass through the cell cycle to the NEXT phase 
What happens when cyclins and cdks are in the INACTIVE form?
Cells can NOT pass through the cell cycle to the NEXT phase 

12. cyclin degrades & breaks apart cyclin degrades & breaks apart

13. What degrades (breaks down) cyclins?
Proteolytic enzymes (proteins)
Break down/degrade cyclins  cause them to fluctuate in [ ]
“PROTEO” means protein
“LYTIC” means break or lyse
REMEMBER:
Cyclin concentration fluctuates (changes)
Cdk concentration stays the SAME

14. Programmed Cell Death (Apoptosis)
If cell doesn’t “pass” checkpoint, it goes through apoptosis
Cell signaling is involved in programmed cell death needed to maintain healthy tissues/ cell function
2 µm
Figure 21.17

15. What other things control cell division?
Both internal and external signals control the cell cycle/cell division…
Internal signals
CDK/Cyclins at checkpoints
External signals
Growth factors
Density dependent inhibition
Anchorage dependence

16. External (outside the cell) Influences on Cell Division
Growth factors
Stimulate other cells to divide
In density-dependent inhibition
Crowded cells stop dividing
Most animal cells exhibit anchorage dependence
Cells must be attached to a structure to divide
Ex: protein of a tissue or another cell

17. Normal mammalian cells.
Cells anchor to dish surface and
divide (anchorage dependence).
When cells have formed a complete single layer, they stop dividing (density-dependent inhibition).
If some cells are scraped away, the remaining cells divide to fill the gap and then stop (density-dependent inhibition).
Normal mammalian cells.
**The availability of nutrients, growth factors, and a substratum for attachment limits cell density to a single layer.
(a)
25 µm
Figure A

18. Loss of Cell Cycle Controls in Cancer Cells
Abnormal dividing cells form tumors
TUMOR= mass or group of abnormal dividing cells

19. Abnormally Dividing Cells make Tumors
Two Types of Tumors:
Benign  “fine”
Clump of cells remain at orginal spot
Malignant  “mean” “cancer”
Loose/destroy attachments to other cells  they can spread or move (called metastasize)!!!

20. Cancer cells = continue to divide w/out rules
Do NOT follow the “rules”
No checkpoints and no density-dependent inhibition or anchorage dependence
Immortal cells (if enough nutrients)
25 µm
Cancer cells usually continue to divide well
beyond a single layer,
forming a clump of overlapping cells.
Figure B

21. Why do cells break the “rules”?
Don’t need growth factors  maybe they make their own growth factors
Mutations in GENES that make proteins involved in control systems!!!

22. Cancer cells are “hungry”…
Angiogenesis
Making of blood vessels towards tumor
Without blood and the nutrients it carries, a tumor would be unable to continue growing.

23. Cancer Treatment
Radiation  destroys DNA in cancer cells (these cells have lost ability to repair damage)
Chemotherapeutic drugs interfere with specific steps in cell cycle
Also effects normal cells 

24. Figure 12.19 Tumor Lymph vessel Blood vessel Glandular tissue
Cancer cell
Blood vessel
Lymph vessel
Metastatic Tumor
Cancer cells invade neighboring tissue. 2
Cancer cells spread through lymph and blood vessels to
other parts of the body. 3
A tumor grows from a single cancer cell. 1
A small percentage of cancer cells may survive and establish a new tumor in another part of the body. 4
Figure 12.19

25. Movies for Review... Angiogenesis Cancer Movie
Angiogenesis