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Biology
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2. 10-3 Regulating the Cell Cycle
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3. Controls on Cell Division
Experiments show that normal cells will reproduce until they come into contact with other cells.
When cells come into contact with other cells, they respond by not growing.
This demonstrates that controls on cell growth and division can be turned on and off.
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4. 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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Cell Cycle Regulators
External Regulators 
Proteins that respond to events outside the cell are called external regulators.
External regulators direct cells to speed up or slow down the cell cycle.
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Cell Cycle Regulators
How is the cell cycle regulated?
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Cell Cycle Regulators
Cell Cycle Regulators
The cell cycle is regulated by a specific protein called cyclin.
The amount of this protein in the cell rises and falls in time with the cell cycle.
Scientists called this protein cyclin because it seemed to regulate the cell cycle.
Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells.
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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 a result, the second cell enters mitosis.
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Cell Cycle Regulators
Internal Regulators 
Proteins that respond to events inside the cell are called internal regulators.
Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell.
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10. Uncontrolled Cell Growth
Cancer is a disorder in which some of the body's own cells lose the ability to control growth.
How are cancer cells different from other cells?
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11. Uncontrolled Cell Growth
Cancer cells do not respond to the signals that regulate the growth of most cells.
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12. Uncontrolled Cell Growth
Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.
All cancer cells are have a defective 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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