Regulating the Cell Cycle
How long does the cell cycle take?




Not all cells move through the cell cycle at the
same rate
Most nerve and muscle cells do not divide once
they have developed
Skin, digestive tract, and bone marrow cells
grow and divide rapidly
Such cells may pass through the cell cycle in a
matter of hours
Cell Cycle Regulators




Controls on cell growth and division can be
turned on and off
Sientist dicovered a protein called cyclin
seemed to regulate the cell cycle
Cyclins regulate the timing of the celll cycle in
eukaryotic cells
There are two types of regulatory proteins:
those that occur inside of the cell and those that
occur outside of the cell
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
occurred inside the cell
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 ccycle
These signals prevent excessive cell growth
and keep the tissues of the body from disrupting
each other
Uncontrolled Cell Growth


The principal reason
that cell growth is
regulated is that the
consequences of
uncontrolled cell
growth is severe,
often fatal
Cancer – a disorder in
which some of the
body's own cells lose
their ability to control
growth
Uncontrolled Cell Growth


Cancer cells do not
respond to the signals
that regulate the
growth of most cells
Cancer cells divide
uncontrollably and
form masses of cells
called tumors
Uncontrolled Cell Growth

All cancers have one
thing in common:
The control over the
cell cycle has broken
down