Regulating the
Cell Cycle
10-3
Controls on Cell
Division
If we look at cells dividing in a petri dish
we can see that they will divide until they
cover the bottom of the dish
Controls on Cell
Division
If we take out all of the cells in the middle
of the dish, the other cells will divide until
the plate is covered again, at which point
cell division will stop occuring
Controls on Cell
Division
This is similar to how the body heals
When the body is cut, broken, or bruised,
cells at the edge of the injury are
stimulated to divide rapidly
Controls on Cell
Division
This stimulation is what creates the
healing of the injury and restoration of the
body
Cell Cycle
Regulators
In the 1980’s two
scientists, Tim Hunt
of the UK and Mark
Kirschner of the
USA discovered
that cells in mitosis
contain a specific
protein that
stimulates Mitosis
to occur
Cell Cycle
This protein is
Regulators
called Cyclin
because it controls
the cell cycle
They did an
experiment where
they injected cyclin
which was found to
stimulate the
growth of spindles,
causing mitosis to
Cyclin
There are many
different types of
Cyclin proteins that
are found in mitotic
cells
Some are known
as internal
regulators while
others are external
regulators
Internal
Regulators
Cyclin proteins that
are internal
regulators respond
to events that are
inside the cell
Examples would be
cyclin that prevents
a cell from entering
anaphase until all
its chromosomes
are attached to
External Regulators
External Regulators
are cyclin proteins
that respond to
events that are
outside the cell
They direct cells to
speed up or slow
down the cell cycle
Cancer
Cell growth and
reproduction must
be monitored
carefully
If it is uncontrolled,
cancer will form
Cancer cells do not
respond to the
signals that
regulate most cells
Cancer
When a cancer
replicates
uncontrollably it will
form a tumor which
can harm
surrounding tissue