Download Cell Cycle and Cell Division

Cell Cycle and Cell Division
Chapter 5
Belk and Borden
Biology: Science for Life
Cell Division
• - the process a cell
undergoes in order to
make copies of itself.
• Why do cells divide?
What is Cancer?
• “mitosis gone mad”
• - a disease that begins
when a single cell
escapes from the
regulation of its own
division
• Tumor
• Benign vs Malignant
The Cell Cycle
• -all the events that
occur when a cell
divides
• -time required can
vary from minutes to
days, depending on
the cell
– Salmonella = 29 min
– Red B. C. = 120 days
DNA & Chromosomes
• DNA as chromatin
strands and
chromosomes
• Sister Chromatids
• Centromere
• Why do chromosomes
form?
Interphase (G1, S, G2)
(about 90% of the cell cycle time)
• Cell grows during all
3 subphases by
making proteins and
organelles
• G1 = first growth
phase
Interphase (G1, S, G2)
(about 90% of the cell cycle time)
• S phase = DNA is
copied (synthesis) so
each daughter cell has
a complete set of
chromosomes at the
end of the cell cycle
Interphase (G1, S, G2)
(about 90% of the cell cycle time)
• G2 phase = second
growth phase
• All through
interphase, the cell is
fulfilling its function
• At maximum volume
to surface ratio, cell
either remains in
interphase or enters
mitosis
Mitosis: Prophase
• Chromatin condenses
into chromosomes
• Each duplicated
chromosome appears
as 2 identical sister
chromatids
• Mitotic spindle begins
to form in cytoplasm
Mitosis: Prometaphase
• Nuclear membrane
disintegrates
• Spindle fibers interact
with chromosomes
• The “dance of the
chromosomes” begins
Mitosis: Metaphase
• Chromosomes are
aligned at middle of
cell
• Identical chromatids
of each chromosome
are attached to spindle
fibers radiating from
opposite poles of the
cell
Mitosis: Anaphase
• Paired centromeres of
each chromosome
separate, freeing sister
chromatids from
eachother
• Each chromatid now a
chromosome
• Sister chromatids are
pulled to opposite
poles of the cell
Mitosis: Telophase
• 2 new nuclei form at
two poles of the cell
where chromosomes
have gathered
• Chromosomes uncoil
and revert to
chromatin form
• Mitosis (division of
one nucleus into two
identical nuclei) is
complete
Cytokinesis
Allium root tip (onion)
a mitosis classic!
Classify Cells relative to
Cell Cycle Phase link
Control of the Cell Cycle
• Cells require nutrients and growth factors to
divide (example PDGF & fibroblasts)
• Density dependent inhibition also regulates cell
division
• Adhesion of cells is also involved. Cells
normally stop dividing if they lose their
anchorage.
• The role of regulatory proteins at the G1
“restriction point” is also critical.
Control of the Cell Cycle
• Regulatory proteins pace and control cell cycle
events at “checkpoints”
• G1 checkpoint—monitors nutritional status,
growth factors, & cell density; “restriction point”
• G2 checkpoint—monitors DNA replication and
cell size
• Metaphase checkpoint—monitors chromosome
attachment to spindle fibers
Mutations
• Changes (errors) in the genes that code for cell
cycle regulatory proteins and tumor suppressor
proteins are involved in cancer
• Proto-oncogenes code for growth factors
• Mutated proto-oncogenes (oncogenes) can
overstimulate cell division and override the G1
checkpoint
• Mutated tumor supressor genes fail to produce
the proteins that prevent tumors
Healthful Decisions to reduce Cancer Risk
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Avoid carcinogenic addictions!
Eat whole foods (fresh fruit and grains)
Exercise regularly to boost immune system
Don’t drink alcohol in excess
Don’t get sunburned
Undergo regular screening and selfexamination