10-3: Regulating the cell cycle
Specialized cells divide at different rates
Some cells never divide
Cardiac: cannot divide
Smooth muscle: can divide
Intestine: 1-2 days, can divide
Nerve cell: cannot divide
RBC: 120 days, cannot divide
Nerve cell: brain
Red blood cell
Cardiac cells
Smooth muscle
Small intestine
Controls on cell division
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Not all cells in the body
divide at the same rate
Cells in a petri dish will
divide until they fill the
dish, then they stop.
If cells are removed,
they’ll grow until the
space is filled again.
Controls on cell division
can be turned on and off.
Cell cycle
regulators
► The
protein cyclin regulates the timing of the cell
cycle in eukaryotic cells. When present, cyclin
triggers cell division.
Internal regulators
► Proteins
Different cyclins active at phases of the
cell cycle
that respond
to internal events in
the cell.
► Some make sure that
the cell doesn’t enter
mitosis until the DNA
is replicated
► Another makes sure
that chromosomes
are attached to the
spindle before
anaphase.
External regulators
► Proteins
that respond
to events outside the
cell.
► Direct the cell to speed
up or slow down the
cell cycle.
► Growth regulators:
important in embryos,
for healing wounds
Cat embryo
Rubber bullet wound
Inhibitors on cell surfaces cause cells to slow
or stop division
Uncontrolled cell
growth
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Cancer is a disease of the
cell cycle
Cancer cells don’t respond
to the signals that regulate
growth.
Leads to uncontrolled cell
growth.
Causes: viruses, tobacco,
radiation exposure
Form masses of cells:
tumors
Melanoma: skin cancer
Oral cancer
Stem cells
► Unspecialized
cells
that have the ability
to turn into any kind
of cell.
► Could replace
damaged cells of
brain, nervous
system.
Human stem cell
stem cell controversy
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Stem cells are produced from human embryos, and are
destroyed when used for research
Raises moral and ethical questions as to their use: Is a
fertilized egg a human being?
Stem cells in umbilical cord blood
Human blastocyte: 100 cells
Adult stem cells
► Adult
stem cells are
found in bone marrow
► Future possibility: a
person’s own stem
cells could be used to
heal previously
untreatable conditions:
spinal cord injury, grow
new liver tissue,
replace heart valves,
reverse the effects of
diabetes.