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NOTES: 10.3-10.4
Regulating the Cell Cycle /
Cell Differentiation
10.3: Regulating the Cell Cycle
Key Concepts:
• How is the cell cycle
regulated?
• How are cancer cells
different from other
cells?
• What causes
cancer?
The Cell Cycle –
review of the basics:
• Genetic information is in the
form of DNA
• Cell cycle = process of cell
division
 The cell grows;
 DNA is copied;
 The contents of the nucleus are
divided;
 Cytoplasm is divided;
 Two new cells exactly like the
original cell!
Also, recall…
• one of the major characteristics of living
things is the ability to GROW
• an adult doesn't have bigger cells, they have
more cells
You can grow too many cells!!!
An Interesting Fact About Cell Division:
• Not all cells move through the
cell cycle at the same rate
– Ex: most muscle cells & nerve
cells do not divide at all once
they have developed
– Ex: skin cells and cells lining
our intestines complete the
cell cycle every 24-28 hours
– Ex: frog embryo cells take less
than one hour!
• Controls can be observed in a lab
– Cells in a petri dish containing nutrient broth
(food) will grow and divide forming a thin layer
– When the cells come into contact with each
other, they stop growing
Controls on Cell Division continued…
• If cells from the center
are removed, growth and
division will continue
until cells are in contact
with each other once
again
• When have you
witnessed this happening
with your own body?
Cell Cycle Regulators
• Several scientists discovered that cells
undergoing cell division (mitosis)
contained a protein/enzyme
• If this protein was injected into a
nondividing cell, the mitotic spindle
would start to form
– Scientists called this protein CYCLIN
– Scientists have since discovered a family of
closely related proteins (cyclins) & dozens
of other proteins that help regulate the cell
cycle
Regulatory Proteins:
• The cell cycle
is controlled
by regulatory
proteins, both
inside &
outside of the
cell
Regulatory Proteins: INTERNAL
• Respond to events occurring inside a cell
• Allow the cell cycle to proceed only
when certain events have occurred in
the cell itself
• Example: some regulatory proteins
make sure a cell does not enter mitosis
until its chromosomes have been
replicated
• Example: a regulatory protein prevents
a cell from entering anaphase until the
spindle fibers have attached to all
chromosomes.
Regulatory Proteins: EXTERNAL
• Respond to events occurring outside the cell
• GROWTH FACTORS: stimulate growth &
division of cells
-important during embryo development &
wound healing
• Other external regulators cause cells to
slow down or stop their cell cycles…this
prevents excessive cell growth & keeps
body tissues from disrupting one another.
Recent studies suggest…
• The portion of interphase
just before DNA
replication is a key control
period in the cell cycle;
• There are several
regulatory proteins
identified as controlling
the cell cycle…
• RECALL: proteins are
coded for by DNA! So…
• A mistake (MUTATION) in the DNA
(GENES) that codes for one or more of
these control factors/enzymes could
lead to a LOSS OF CONTROL OF THE
CELL CYCLE.
• What can happen if the
cell cycleis not regulated
so carefully?
– CANCER!!
• Cancer cells do not
respond to signals that
regulate the growth of
most cells.
• The result? They form
masses of cells called
TUMORS that can damage
the surrounding tissues
– Benign vs. malignant
• Cancer cells can also break
off and spread throughout
the body METASTASIS
Old Mastectomy
Vs.
New Mastectomy
BREAST TUMOR
Recent Research
• Many cancer cells have a defect in a
gene called p53
– The protein made from this gene normally
halts the cell cycle until all chromosomes have been
replicated properly (without mutations)
– If it isn’t working, damaged DNA can replicate
– The cell may have lost the information it needs to
respond to growth control signals
• Cancer is a disease of the cell cycle
Cancer is the 2nd leading cause of
death in the U.S.
• It can affect any tissue,
but the most commonly
affected are:
 lung
 colon
 breast
 prostate
What causes the loss of growth
control?
• Smoking tobacco
• Radiation exposure
• Viral infection
HUMAN LUNG
Cancer Prevention:
● There is a clear link between healthy
lifestyle and reducing the incidence of
cancer;
● Diet low in fat and high in fiber;
(fruits, vegetables, & grains)
● Vitamins and minerals;
(A, C, E, & calcium)
● Exercise;
● Wear sunscreen
● DON’T SMOKE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(Seriously!! This should be a no-brainer!!)
Treatments
• surgery (for benign tumors)
• radiation
• chemotherapy
10.4: Cell Differentiation
Key Concepts:
• How do cells become
specialized for
different functions?
• What are stem cells?
• What are some
possible benefits &
issues associated
with stem cell
research?
Cell Differentiation:
● the process by which cells
become specialized for
different functions;
● we all started as an
individual fertilized egg cell
 embryo  adult
organism
● cell differentiation is
controlled by a number of
interacting factors in an
embryo…many of which we
still don’t completely
understand!
STEM CELLS:
● how do so many
specialized,
differentiated cell types
develop from just a
single cell?
● such a cell is said to be
TOTIPOTENT
● TOTIPOTENT = able to
develop into any cell type in
the body
● PLURIPOTENT = able to
develop into most of the
body’s cell types
STEM CELLS:
● STEM CELLS = the
unspecialized cells from
which differentiated cells
develop
● TYPES of stem cells:
● EMBRYONIC: pluripotent
cells found in early embryo
stages…mouse embryonic
stem cells have been
triggered to differentiate into:
nerve cells, muscle cells, &
even sperm & egg cells!
STEM CELLS:
● TYPES of stem cells:
● ADULT: groups of cells that differentiate
to renew & replace cells in the adult
body; more limited than embryonic stem
cells
● Example: adult stem cells in the bone
marrow can develop into several types
of blood cells
● Example: adult stem cells in the brain
can produce neurons or nerve cells
STEM CELLS:
● BENEFITS of Stem Cell Research:
● stem cells offer excellent prospects to
repair cellular damage that is the cause
of many human life-threatening
conditions:
● Example: heart attacks destroy heart
cells
● Example: strokes & spinal cord injuries
destroy nerve cells & cause paralysis
STEM CELLS:
● ETHICAL ISSUES:
● adult stem cells can be harvested from
willing adult donors
● embryonic stem cells are harvested from
early stage embryos…this has led to
many ethical discussions involving
issues of life and death…
● in the future, technology may help to
reduce these ethical concerns (i.e.
reprogram an adult stem cell to behave
like an embryonic stem cell)