1. Regulating the Cell Cycle
Where do cells come from? Where did the cell in my cheek come from?
-All cells come from pre-existing cells (cell theory)
What is the earliest cell then in our body?
-all cells originated from your egg cell
-imagine, one tiny cell grew for over 10 months into a baby
-how much does a baby weigh?
- 7lbs
How many cells does the human body have? Trillions
If the skin cell has the same DNA as the egg cell, why hasn’t your skin cell grown to be 7lbs
Why aren’t our trillions of cells 7lbs each?
This is gene regulation!
1/3 of genes are turned off before we are even born
If these genes turn back on = cancer
Oncogenes = off: growth gene
Tumor suppressor genes = on
If liver and skin cells have the same genes, but the liver cell has different genes ON than the skin cell

2. Controls on Cell Division
Density-dependent Inhibition
Cells will continue to grow until cells come into contact with other cells (depends on density of population)
Contact inhibition: chemicals released by cells so they stop dividing as they become crowded.

3. When you are cut…
Cells at the edges of the injury are stimulated to divide rapidly
When close to healing, rate of division slows down
Controls on growth are restored and everything returns to normal

4. Growth factors are proteins secreted by cells that stimulate other cells to divide
After forming a single layer, cells have stopped dividing.
Growth Factor
Providing an additional supply of growth factors stimulates further cell division.
The cells are still in a single layer, but smaller and more numerous
Most cells require growth factors in order to begin dividing, and they stop dividing when they run out of these substances.
Flooding a layer of nondividing cells with growth factor stimulates the cells to grow to a greater density than they would otherwise.

5. 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
Cell cycle control system is a set of proteins that both triggers and coordinates major events in the cell cycle.
Control system
M checkpoint
G2 checkpoint
Figure 8.9A

6. Cell cycle control system
The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division
Growth factor
Plasma membrane
Relay proteins
Receptor
protein
G1 checkpoint
Growth Factors
Proteins that bind to receptors on the cell surface
Stimulate the growth and division of cells
Important in embryonic development and wound healing
Signal transduction pathway
Cell cycle control system

7. Internal regulators exist at checkpoints throughout the cell cycle.
Allow the cell cycle to proceed only when certain processes have happened inside the cell
Check to see that a cell doesn’t enter M phase until all chromosomes have been replicated
CDK & Cyclin

8. Cancer

9. Uncontrolled Cell Growth
Cancer is a disorder in which some of the body’s own cells lose the ability to control growth
Malignant cells are cancerous cells
Apoptosis Animation
Apopotosis Multiple
Apoptosis Explanation

10. Uncontrolled Cell Growth
Cancer cells do NOT respond to signals that regulate cell growth
They will divide uncontrollably and form tumors
Cancerous cells may break loose from tumors and spread throughout the body (metastasize)

11. What causes cancer? A mutation to the DNA that controls the cell cycle
The average cancer cell has between 6 and 8 different mutations
What do these mutation affect?
Genes that control the cell cycle
Genes that control cell death

12. Cell Cycle controlled by:
2 types of genes
Proto-oncogenes
Encode proteins that promote cell division (gas pedal on a car: “GO!”)
Tumor-suppressor genes
Encode proteins that inhibit cell division (brake pedal on a car: “STOP!”)
Cancerous cells have mutated proto-oncogenes AND tumor suppressor genes = “Always on GO!”
Which of these do you think is mutated in cancer cells?
Tumor-suppressor gene

13. What causes the loss of growth control?
All cancers have one thing in common:
The control over the cell cycle has broken down
Some cancer cells no longer respond to external growth regulators
Some cancer cells fail to produce internal regulators to ensure orderly growth
Defect in gene p53

14. Gene p53
Main function is to halt the cell cycle until all chromosomes have been properly replicated
Damaged/Defective p53 cause the cells to lose the information needed to respond to signals that would control their growth

15. Cancer Benign tumors remain clustered and can be removed.
Cancer Cell Behavior
Benign tumors remain clustered and can be removed.
Malignant tumors metastasize, or break away, and can form more tumors.
cancer cell
bloodstream
normal cell
Several mutations to the DNA that controls the cell cycle occurs.
The p 53 gene does not find the mutations and destroy the cell.
Cells start to divide uncontrollably.
The new cells formed are also cancerous.
Large #’s of cancerous cells from clumps called tumors.
Tumors out-compete normal healthy cells for nutrients. The normal cells die.
Tumors break apart and spread cancer cells to other tissues and organs and out-compete the normal cells there killing them