Regulating the Cell Cycle
10.3
WARM UP:
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Label the next blank page in your notebook  10.2
Review Warm Up.
Copy and answer the following questions on this page:
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1. How does the structure of chromosomes differ in
prokaryotes and eukaryotes?
2. During which phase of the cell cycle are chromosomes
replicated?
3. What happens during each of the 4 phases of mitosis? Write
1 sentence for each phase.
4. What is cytokinesis and why does it occur?
5. How does cytokinesis differ in animal and plant cells?
Controls on Cell Division:
How is the cell cycle regulated?
Discovery of Cyclins:
 In
the early 1980s, biologists
discovered a protein in cells that
were going through mitosis  cyclin
 Biologists have since discovered a
family of proteins known as cyclins
that regulate the timing of the cell
cycle in eukaryotic cells
Regulatory Proteins:
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Since the discovery of cyclins, scientists have discovered
dozens of other proteins that also help regular the cell
cycle.
The cell cycle is controlled by regulatory proteins both
inside and outside the cell.
Internal Regulators:
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Respond to events occurring inside a cell
Allow the cell cycle to proceed only when certain events
have occurred in the cell itself
Example:
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several regulatory proteins make sure a cell does not enter
mitosis until its chromosomes have replicated
External Regulators:
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Proteins that respond to events outside the cell
direct cells to speed up or slow down the cell cycle
Growth factors = important group of external regulatory
proteins
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Stimulate the growth and division of cells
Important during embryonic development and wound healing
Other external regulators cause cells to slow down or
stop their cell cycles
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Prevents excessive cell growth and keeps body tissues from
disrupting one another
Apoptosis:
As new cells are produced, other cells die.
 Cells end their life cycle in two possible ways:
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By accident due to damage or injury
May be programmed to die = apoptosis
Once apoptosis is triggered…
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1. the cell and its chromatin shrink
2. part of the cell’s membranes break off
3. neighboring cells then quickly clean up the
cell’s remains
Cancer: Uncontrolled Cell Growth
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Cancer = a disorder in which body cells lose the ability to
control growth
Cancer cells do not respond to the signal that regulate the
growth of most cells
Cancer cells form a mass of cells called a tumor
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Not all tumors are cancerous
Some tumors are benign = noncancerous
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Do not spread to the surrounding healthy tissue or to other parts of the
body
Cancerous tumors are malignant  invade and destroy
surrounding healthy tissue
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As cancer cells spread, they absorb the nutrients needed by other cells,
block nerve connections, and prevent the organs they invade from
functioning properly
What causes cancer?
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By defects in the genes that regulate cell growth and
division
Several sources:
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Smoking/chewing tobacco
Radiation exposure
Other defective genes
Viral infection
Some cancer cells will no longer respond to external
growth regulators, and some fail to produce the internal
regulators that ensure orderly growth.
What causes cancer? (cont.)
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A lot of cancer cells have a defect in a gene called p53 –
normally stops the cell cycle until all chromosomes have
been properly replicated
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damaged or defective p53 genes cause cells to lose the
information needed to respond to signals that normally control
their cell growth
Treatments for Cancer:
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1. Tumor is removed
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2. Radiation
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When a cancerous tumor is found, it can often be removed by
surgery.
Example: skin cancer
Carefully targeted beams of radiation
Cancer cells are vulnerable to radiation because they grow
rabidly and need to copy their DNA more quickly than most
normal cells
3. Chemotherapy
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Chemical compounds that kill cancer cells
Also interferes with cell division in normal, healthy cells
Serious side effects in many patients