1. 10-3 Regulating the Cell Cycle
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2. Controls on Cell Division
Contact Inhibition
Cells in a petri dish will continue to grow until they come into contact with other cells.
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3. Controls on Cell Division
Contact inhibition – Cells stop growing when in contact with other cells
Cell growth can be turned on and off by internal and external regulators.
Once cells reach adult stage they grow and divide at different rates depending on cell type.
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Cell Cycle Regulators
Cell Cycle Regulators
Cell cycle is regulated by a specific protein called cyclin.
amount of protein rises and falls in time with the cell cycle
Cyclin directs the cell to go into mitosis.
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Cell Cycle Regulators
Cyclins were discovered during a similar experiment to this one.
The timing of the cell cycle is regulated by cyclins. When cytoplasm from a cell in mitosis is injected into another cell, the second cell enters into mitosis. The reason for this effect is a protein called cyclin, which triggers cell division.
A sample of cytoplasm is removed from a cell in mitosis.
The sample is injected into a second cell in G2 of interphase.
As result, the second cell enters mitosis.
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Cell Cycle Regulators
Internal Regulators 
Internal regulators - Proteins that respond to events inside the cell
Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell.
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Cell Cycle Regulators
External Regulators 
External Regulators - proteins that respond to events outside the cell.
External regulators direct cells to speed up or slow down the cell cycle.
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What is the Life span of a human cell? It depends on what cell it is. e.g. blood cell, skin cell, stomach tissue cell Recent studies have shown that few cells live as long as the individual they belong to without renewal. A majority, if not all, the cells making up the cerebral cortex belong to this small group. The life span of some other human cells are as follows:
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9. Lifespan of select human cells:
Platelets days
Skin epidermal cells weeks
Lymphocytes -- 2 months - a year
Red blood cells -- 4 months
Stomach lining cells -- 2 days
Macrophages -- months - years
Endothelial cells -- months - years
Pancreas cells -- 1 year or more
Bone Cells years
 Cell Type – Lifespan
Granulocytes hours to 3 days
Stomach lining cells -- 2 days
Sperm cells days
Colon cells days
Epithelia of small intestine -- 1 week or less
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10. Uncontrolled Cell Growth
Uncontrolled Cell Growth xxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Cancer is a disorder in which some of the body's own cells lose the ability to control growth.
Cancer cells
divide uncontrollably
form masses of cells called tumors
Tumors can damage surrounding tissues
Metastatic cancer cell – cell that breaks loose from tumor and spreads throughout the body
Cancer is usually caused by a defect in gene p53
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10-3
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10-3
The cell cycle is believed to be controlled by proteins called
spindles.
cyclins.
regulators.
centrosomes.
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10-3
Proteins that respond to events inside the cell are called
internal regulators.
external regulators.
cyclins.
growth factors.
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10-3
Once a multicellular organism reaches adult size, the cells in its body
stop dividing.
grow and divide at different rates, depending on the type.
have the same life span between cell divisions.
undergo cell division randomly.
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10-3
One effect of an internal regulator is that a cell will not begin mitosis until
it becomes too large.
the cell’s growth is stimulated.
it is in physical contact with other cells.
all its chromosomes have been replicated.
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10-3
One factor common to almost all cancer cells is
a lack of cyclin.
a defect in gene p53.
exposure to tobacco smoke.
exposure to radiation.
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