1. Interest Grabber Answers
Knowing When to Stop
Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.
1. How do you think the body repairs an injury, such as a cut on a finger?
The cut is repaired by the production of new cells through cell division.
2. How long do you think this repair process continues?
Cell division continues until the cut is repaired.
3. What do you think causes the cells to stop the repair process?
Students will likely say that when the cut is filled in, there is no room for more cells to grow.

2. REGULATING the CELL CYCLE

3. Control of Cell Division
Section 10-3
If center cells are removed, cells near the space will start to grow again.
SHOWS: Cell division
genes can be turned on
and off
Cells grow until they touch other cells

4. CELL DIVISION GENES
EXAMPLE: Cell division genes can be ________ in case of injury.
Cells near injury are
stimulated to divide
to heal and replace damaged/missing cells
and shut off when the
repair has been made.
turned on

5. CELL DIVISION GENES Some cells divide frequently
(some human skin cells divide once/hour)
Some cells divide occasionally
(liver cells divide about once/year)
Some cells don’t divide once they form
(nerve cells)

6. CELL CYCLE REGULATORS
In early 1980’s scientists discovered a protein in dividing cells that caused a
______________to form in
_______________ cells
Mitotic spindle
NON-dividing

7. CELL CYCLE REGULATORS Levels of this protein rose and fell with
the cell cycle so it was named
__________ because it seemed to control the cell cycle.
A whole family of CYCLINS have since been discovered that regulate the _____________________
in EUKARYOTIC CELLS
CYCLIN
TIMING of CELL CYCLE

8. OTHER REGULATORS INTERNAL
______________ REGULATORS Proteins that respond to events inside
the cell.
Allow cell cycle to proceed only if
certain processes have happened
EX: Cell can’t enter mitosis until all the
chromosomes have been copied

9. Three Cell Cycle Checkpoints
1st checkpoint: at the end of G1 (checks that the cell has doubled in size)
2nd checkpoint: at the end of G2 (checks that the cell can divide)
3rd checkpoint: at the end of metaphase (checks to see that replicated chromosomes are attached to spindle fibers)

10. OTHER REGULATORS EXTERNAL
______________ REGULATORS Proteins that respond to events outside
the cell.
Signals tell cell to speed up or slow
down the cell cycle
EX:
Growth factors stimulate cells to divide Especially important during wound healing and
embryo development

11. EXTERNAL REGULATORS Molecules on the surface of neighboring
cells act as signals to slow down
or stop the
cell’s cycle.
These signals prevent
excessive growth and
keep tissues from
disrupting each other.

12. Cancer cells have lost control of their cell division genes
SEM Image by: Riedell
CHO (Chinese Hamster Ovary) cells in culture

13. NO CONTACT INHIBITION Cancer cells don’t stop when they touch nearby
they just keep growing!
That’s what makes
a tumor.
See a video

14. Cancer cells Carcinogens Don’t stop dividing
Like a “car with no brakes”
Can spread to new places (METASTASIS)
______________ are substances that can damage DNA and cause cancer
Ex: Cigarette smoke (OR CHEW), Radiation, chemicals in environment, even viruses,
Carcinogens

15. Cancer cells
Cancer is complicated and can have many causes, but all cancers have one thing in common . . .…
They have lost control over their _____________.
Many cancers cells have a damaged or defective
gene called _____, so they can’t respond to
normal cell signals to control their growth.
CELL CYCLE
p53

16. He La cells