1. Cell Cycle Regulation

2. Factors that affect cell division
Most animal cells divide only when stimulated, and others not at all
In laboratory cultures, most normal cells divide only when
Attached to a surface—anchorage dependent
Have enough space
Have enough growth factor

3. Cell Cycle Control System
G1 checkpoint
Control
system S G1 G2 M
M checkpoint
G2 checkpoint

4. Growth factors signal the cell cycle control system
Proteins within the cell control the cell cycle
Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide
G1 checkpoint
M checkpoint
G2 checkpoint
Control system
Figure 8.9A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

5. For many cells, the G1 checkpoint is the “restriction point”
A go-ahead signal indicates that the cell will complete the cycle and divide
In the absence of a go-ahead signal, the cell may exit the cell cycle and remain in the non-dividing state called G0 phase
Many human cells are in the G0 phase until they die—muscle and nerve cells

6. Cell cycle control system
G1 Checkpoint:
The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division
Growth factor
Figure 8.8B
Cell cycle control system
Plasma membrane
Receptor
protein
Signal transduction pathway
G1 checkpoint
Relay proteins
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

7. Cells must have Growth Factors
Growth factors are proteins secreted by cells that stimulate other cells to divide
After forming a single layer, cells have stopped dividing.
Providing an additional supply of growth factors stimulates further cell division.
Figure 8.8B

8. Cells are Density Dependent
Cells continue dividing until they touch one another (density-dependent inhibition)
Cells anchor to dish surface and divide.
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 dish with a single layer and then stop (density-dependent inhibition).
Figure 8.8A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

9. G2 Checkpoint: Repair enzymes make sure DNA has been copied correctly
There are plenty of proteins (growth factors) and organelles present
Control system
Figure 8.9A
G2 checkpoint

10. Metaphase Anaphase M Checkpoint:
Anaphase does not begin until all chromosomes are attached to spindle at metaphase plate
Metaphase
Anaphase

11. Cancer cells: Growing out of Control
Cancer cells have abnormal cell cycles
They divide excessively and can form abnormal masses called tumors
Cancer cells do not respond normally to the body’s control mechanisms and divide excessively
Density-independent—make their own growth factors and continue to divide uncontrolled (“immortal”)
Anchorage-independent
Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

12. Abnormal cells that escape cell-cycle control are products of mutated or transformed normal cells
May proliferate to form a tumor—an unregulated growing mass of cells within normal tissue
Benign tumor—if cells remain at the original site
Malignant tumor—if mass impairs normal function of one or more organs of the body
Excessive proliferation
Cells with unusual number of chromosomes
Aberrant metabolism
Detaches and migrates through body (metastasis)

13. Malignant tumors can invade other tissues and may kill the organism
Lymph vessels
Tumor
Glandular tissue
Metastasis 1 2 3
A tumor grows from a single cancer cell.
Cancer cells invade neighboring tissue.
Cancer cells spread through lymph and blood vessels to other parts of the body.
Figure 8.10