Download Regulating the cell cycle

REGULATING
THE CELL CYCLE
Chapter 10
 Not
all cells in the body go through the
cell cycle at the same rate.

For example: muscle and nerve cells
never go through mitosis after they
mature.

Liver cells go through mitosis about
once a year.
 Skin and intestinal cells go through
mitosis every few hours.
WHAT CONTROLS THE RATE OF CELL
DIVISION?
 1.
Contact inhibition: chemicals released by
cells so they stop dividing as they become crowded.
 Contact inhibition can be turned on or off as
needed.

Cyclins:
 proteins that regulate the timing of the
cell cycle.
 trigger cell division.
 A. Internal regulators: several proteins
make sure the cell cycle does not proceed
unless certain processes have happened
inside the cell.
 For example: one protein makes sure the
cell does not go into mitosis until all of the
DNA has replicated.

2.

B. External regulators: several
proteins that respond to events
outside the cell and direct the cell to
either speed up or slow down the cell
cycle. Growth factors are among
the most important external
regulators.
 3.
Apoptosis: programmed cell
death or cell suicide
 cell fragments are quickly ingested
by other cells
WHAT HAPPENS IF THE RATE OF THE CELL
CYCLE IS NOT CONTROLLED?
CANCER –
body’s
own cells lose the
ability to control growth
and division and start to
divide uncontrollably.
WHAT CAUSES CANCER? A MUTATION TO THE
DNA THAT CONTROLS THE CELL CYCLE
 The
accumulation of multiple
mutations transform a normal cell
into a cancer cell.
 average cancer cell contains between
six -eight different mutations. These
mutations affect:
1genes
that control the cell cycle
2genes that control cell death
3genes that allow the cell to
obtain nutrients and migrate
through out the body.
CANCER CELLS IGNORE THE SIGNALS
THAT REGULATE THE CELL CYCLE
cell
cycle is controlled by the
products of two classes of genes,
proto-oncogenes (promote cell
division * GO* and tumor
suppressor genes (suppress cell
division *STOP* )
 DNA
mutations can be caused by
environmental factors (also called
mutagenic agents) such as:
UV
radiation
Viruses
Toxic chemicals (cigarettes)
HOW DOES CANCER PROGRESS?
Several mutations to the DNA
that controls the cell cycle occurs.
 2. The p 53 gene does not find the
mutations and destroy the cell.
 3. Cells start to divide
uncontrollably.

1.
new cells formed are also
cancerous.
 5. Large #’s of cancerous cells from
clumps called tumors.
 6. Tumors out-complete normal
healthy cells for nutrients. The
normal cells die.

4. The

Tumors break apart and
spread cancer cells to other
tissues and organs and outcompete the normal cells
there killing them. This is
called metastasis.
7.

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