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5.3 Regulation of the Cell Cycle
Summarize how cell regulation controls and
coordinates cell growth and division and
allows cells to respond to the environment,
and recognize the consequences of
uncontrolled cell division.
5.3 Regulation of the Cell Cycle
Cell cycle regulation is necessary for healthy
5.3 Regulation of the Cell Cycle
•The cell cycle is driven by a chemical control
system that both triggers and coordinates key events
in the cell cycle.
•The cell cycle control system is regulated at certain
•Signals from inside the cell (internal signals) and
from outside the cell (external signals) are involved
in turning the process of cell division off and on.
5.3 Regulation of the Cell Cycle
Internal and external factors regulate cell division.
• An internal signal involves the cell sensing the presence
of chemicals, called enzymes, which are produced inside
the cell.
• Two of the most important internal factors are kinases
and cyclins.
5.3 Regulation of the Cell Cycle
• An external signal involves the cell sensing the presence of
a chemical (such as a growth factor) which was produced in
other specialized cells.
• Cells can also respond to physical signals from their
• Cells sense when they are too closely packed and cell
division is turned off.
• Cells sense when they are not in contact with a
surface and cell division is turned on.
5.3 Regulation of the Cell Cycle
Sometimes cells do not respond normally to the body’s
control mechanisms and divide excessively.
•Cancer cells are an example of cells that do not heed the
normal signals which shut down the cell division process.
•They continue to divide even when they are very densely
packed and/or there is no growth factor present.
•Cancer begins when a single cell is transformed into a
cancer cell, one that does not heed the regulation
5.3 Regulation of the Cell Cycle
• Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– caused by a cell’s production of self-destructive
– occurs in
webbed fingers
of infants
5.3 Regulation of the Cell Cycle
Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.
– Benign tumors remain clustered and can be removed.
– Malignant tumors metastasize, or break away, and can
form more tumors.
normal cell
cancer cell
5.3 Regulation of the Cell Cycle
•Normally the body’s immune system will recognize that the
cell is damaged and destroy it, but if it evades destruction, it
will continue to divide and each daughter cell will be a cancer
•A mass of these cells that invades and impairs the functions
of one or more organs is called a malignant tumor.
•A benign tumor is a mass of abnormal cells that remains at
the original site.
•Cancer cells may also separate from the original tumor, enter
the blood and lymph vessels of the circulatory system, and
invade other parts of the body, where they grow to form new
5.3 Regulation of the Cell Cycle
• Cancer cells do not carry out necessary functions.
• Cancer cells come from normal cells with damage to
genes involved in cell-cycle regulation.
5.3 Regulation of the Cell Cycle
• Carcinogens are substances known to promote cancer.
• Standard cancer treatments typically kill both cancerous
and healthy cells.
5.3 Regulation of the Cell Cycle
Complete p. 47-48 in Study Guide workbook