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Cell Cycle Clock,
Mitosis, and
Cancer Biology
Lemon Bay High School
Susan Chabot
Cell Division – Mitosis of a Zygote
The Cell Cycle Clock
G0 Quiescence
Work but no Mitosis
The Cell Cycle Control System
• is like a clock
• regulated by
both internal and
external controls
• has specific
where the cell
cycle stops until
a go-ahead
signal is
The Cell Cycle Control System
• For many cells, the G1 checkpoint is
the most important.
• If a cell receives a go-ahead signal at the
G1 checkpoint, it will usually complete the
S, G2, and M phases and divide.
• If the cell does not receive the go-ahead
signal, it will exit the cycle, switching into
a non-dividing state called the G0 phase
The Eukaryotic Cell Cycle is Regulated by
a Molecular Control System
• The frequency of cell division varies with the
type of cell.
– Not all cells divide at the same time, for the same
reasons, or as frequent as other cells.
• These differences result from genetic
regulation at the molecular level.
– This controls the RATE and TIMING of cell
Types of Cells
All cells in a eukaryotic, multicellular organism can be
placed in 1 of 3 categories based on their ability to
• Labile
• Stabile
• Permanent
Contact Inhibition
• Cells
do not normally grow or divide when in
contact with other cells.
 Ex: Cultured cells in a petri dish
 will divide until they form a layer one cell
thick and then stop when make contact w/
other cells.
 Called contact inhibition of cell growth.
• Cells
can migrate in culture
 Stop moving when touch other cells due to
contact inhibition of cell movement.
Contact inhibition
Does not occur in Cancerous
Cancerous cells continue growing and moving when
they touch other cells.
They pile up and they migrate to other parts of the body -- the
cancer spreads.
Growth Factors
Chemical messages that control the cell cycle
Characteristics of Cancer
Characteristics of Cancer Cells…
1. Have lost the genetic ability to stop
Cancer is heritable—Cancer cells give rise to
cancer cells
2. Immortal
3. Not subject to contact inhibition
4. Metastasize: Spread into other tissues
5. Are De-differentiated
less specialized than the cell it came from)
2. Basal cell carcinoma
1. Normal cell growth
Only one daughter
Cell divides
Actively dividing cells
(basal cells)
Both daughter
cells divide
Slide 12
Growth Factors
Stimulate Cell Division
• Diffuse
through the body making contact with
many different cells
• Bind
to Membrane Receptors, like a key
fitting into a lock.
 stimulate a pathway inside cell that leads to
cell division.
• Different
cell types are stimulated by
different growth factors.
Cancer: It’s all in the Genes
• Proto-oncogenes:
 “pre-cancer
 Genes that code for growth factors
 Active in actively dividing tissues (e.g.
 Sometimes mutate into......
• Oncogenes:
mutated proto-oncogene
 Genes that cause cancer
 Produce too much growth factor
 Over stimulate mitosis
Tumor Suppressor Genes
• Tumor
Suppressor Genes
 Code
for Proteins that turn off cell
• p53
 Codes
for a protein that stops the cell
cycle after G1
 Half of all cancers involve a mutation of
The Role of the
Environment in Causing
• Certain
Viruses, toxins, or Radiation may lead to
a p53 mutation
2nd p53 mutation may lead to one of the
following cancers
Bladder, blood, brain, breast, colon, esophagus, liver,
lung, spleen, thyroid, etc.
TMN System
T = Tumor Size
N = Lymph Node Involvement
M = Metastasis
Therapeutic Strategies for
Treating Cancer
• Slash
– Surgical Removal
• Burn
– with Radiation
• Poison
– with Chemotherapy
• Since
cancer is uncontrolled cell
division, all chemotherapeutic
treatments involve the cell cycle.
 Phase-specific chemotherapies
Prevent cells from entering S-phase
Block the S-phase
Block the M-phase (mitosis)
Cells Affected by
• Chemo
• Which
may affect all dividing cells
cells divide rapidly?
 Hair follicle cells
 Skin cells
 Cells lining digestive tract
 Blood stem cells
• What
would be the side effects?
Common Warning Signs of Cancer:
C - change in bowel or bladder habits
A - a sore that does not heal
U - unusual bleeding or discharge
T - thickening or lump in the breast or any part of
the body
I - indigestion or difficulty swallowing
O - obvious change in a wart or mole
N - nagging cough or hoarseness