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Cell Division
Ch. 10
Biology
Ms. Haut
Functions of Cell Divsion
1. Replacement of lost or damaged cells
2. Growth—multicellular organisms grow
and develop from single cell (fertilize egg)
3. Cell Reproduction
Prokaryotes
• Genes usually carried on a single circular DNA
molecule
• DNA has a few proteins and is attached to the
plasma membrane at one point
• DNA not bounded by membrane (nucleoid region)
• Cells divide by binary fission
http://www.karlloren.com/biopsy/images/TEM-Fission_rod.jpg
Binary Fission
• Before dividing, an exact copy
of the chromosome is made
• The attachment point divides
so the 2 new chromosomes
are attached at separate parts
of the membrane
• The cell elongates and a new
plasma membrane is added
and the attachment points
move apart
• The plasma membrane and
new cell wall pinch through
the cell, separating the 2
chromosomes into two new,
identical cells
Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings
Cell Division in Eukaryotes
• In eukaryotes, cell division occurs in two major
stages.
• The first stage, division of the cell nucleus, is
called mitosis.
• The second stage, division of the cell
cytoplasm, is called cytokinesis.
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Chromosomes
• Genetic information is
passed from one
generation to the next
on chromosomes.
• Before cell division,
each chromosome is
duplicated, or copied.
http://www.anselm.edu/homepage/jpitocch/genbio/sphase.JPG
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Chromosomes
• Each chromosome consists of two identical “sister”
chromatids.
• Each pair of chromatids is attached at an area called
the centromere.
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http://www.uic.edu/classes/bios/bios100/labs/realchromo.jpeg
• When the cell divides,
the chromatids
separate.
• Each new cell gets one
chromatid.
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http://www.anselm.edu/homepage/jpitocch/genbio/sphase.JPG
Chromosomes
The Cell Cycle
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http://www.pitt.edu/~super1/lecture/lec19281/img004.GIF
• The cell cycle is the series of events that cells go through
as they grow and divide.
• Interphase is the period of growth that occurs between
cell divisions.
During the Cell Cycle
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http://www.pitt.edu/~super1/lecture/lec19281/img004.GIF
• a cell grows
• prepares for division
• divides to form two daughter cells, each of which
begins the cycle again
The Cell Cycle
• The cell cycle consists of
four phases:
–
–
–
–
G1 (First Gap Phase)
S Phase
G2 (Second Gap Phase)
M Phase
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Events of the Cell Cycle
• During G1 phase
(First Gap Phase)
– the cell increases in
size
– synthesizes new
proteins and
organelles
http://media.photobucket.com/image/interphase%20stages/udyama/cycle.gif
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Events of the Cell Cycle
• During the S phase,
– chromosomes are
replicated
– DNA synthesis takes
place
– Once a cell enters
the S phase, it
usually completes
the rest of the cell
cycle.
http://media.photobucket.com/image/interphase%20stages/udyama/cycle.gif
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Events of the Cell Cycle
• The G2 phase
(Second Gap Phase)
• organelles and
molecules required
for cell division are
produced
• Once G2 is complete,
the cell is ready to
start the M phase—
Mitosis
http://media.photobucket.com/image/interphase%20stages/udyama/cycle.gif
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• Mitosis
Mitosis
– Biologists divide the events of mitosis into four
phases:
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
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Prophase
• Prophase is the first
and longest phase of
mitosis.
• The centrioles
separate and take up
positions on
opposite sides of the
nucleus.
Prophase
• The centrioles lie in a
region called the
centrosome.
• The centrosome
helps to organize the
spindle, a fanlike
microtubule
structure that helps
separate the
chromosomes.
Prophase
• Chromatin condenses
into chromosomes.
• The centrioles
separate and a spindle
begins to form.
• The nuclear envelope
breaks down.
Prophase
http://micro.magnet.fsu.edu/cells/fluorescencemitosis/images/prophasesmall.jpg
Metaphase
• Centrosomes at opposite poles of
cell
• The chromosomes line up across
the center of the cell.
• Centromeres of all chromosomes
are aligned with one another, and
sister chromatids straddle
metaphase plate
• Microtubules connect the
centromere of each chromosome
to the poles of the spindle.
• Mitotic spindle completely
formed
Metaphase
http://micro.magnet.fsu.edu/cells/fluorescencemitosis/images/
Anaphase
• The sister
chromatids separate
into individual
chromosomes.
• The chromosomes
continue to move
until they have
separated into two
groups.
Anaphase
http://micro.magnet.fsu.edu/cells/fluorescencemitosis/images/
Telophase and Cytokinesis
• Daughter nuclei form at two poles
of cell
• A new nuclear envelope forms
around each cluster of
chromosomes.
• Chromosomes gather at opposite
ends of the cell and uncoil back
into chromatin
• Mitotic spindle disappears
• Nucleolus reforms
Telophase
http://micro.magnet.fsu.edu/cells/fluorescencemitosis/images/
Cytokinesis
• During cytokinesis,
the cytoplasm
pinches in half.
• Process overlaps with
telophase of mitosis
• Each daughter cell
has an identical set of
duplicate
chromosomes
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Cytokinesis
• Occurs differently in plants and animals
– Cleavage furrow forms in animal cells
– Cell plate forms in plant cells
Cell Plate
Cleavage
furrow
Cytokinesis
Figure 8.9a
Figure 8.9b
Cell Division
The series of events that cells go through as they
grow and divide is called
a)
b)
c)
d)
the cell cycle.
mitosis.
interphase.
cytokinesis.
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The phase of mitosis during which the
chromosomes line up across the center of the cell is
a)
b)
c)
d)
prophase.
metaphase.
anaphase.
telophase.
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Cytokinesis usually occurs
a)
b)
c)
d)
at the same time as telophase.
after telophase.
during interphase.
during anaphase
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DNA replication takes place during the
a)
b)
c)
d)
G2 phase of the cell cycle.
G1 phase of the cell cycle.
S phase of the cell cycle.
M phase of the cell cycle.
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During mitosis, “sister” chromatids separate from
one another during
a)
b)
c)
d)
telophase.
interphase.
anaphase.
metaphase.
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• END OF SECTION
Cell Cycle Regulation
Ch. 10
Biology
Ms. Haut
Controls on Cell Division
• Experiments show that normal cells will
reproduce until they come into contact with
other cells.
• When cells come into contact with other cells,
they respond by not growing.
• This demonstrates that controls on cell growth
and division can be turned on and off.
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Controls on Cell Division
• Contact Inhibition
Cells attach to dish surface and divide.
When cells have formed a complete
single layer, they stop dividing (contact
inhibition).
If some cells are scraped away, the
remaining cells divide to fill the dish
with a single layer and then stop
(contact inhibition).
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Cell Cycle Regulators
• The cell cycle is regulated by a specific protein.
• The amount of this protein in the cell rises and
falls in time with the cell cycle.
• Scientists called this protein cyclin because it
seemed to regulate the cell cycle.
• Cyclins regulate the timing of the cell
cycle in eukaryotic cells.
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Internal Regulators
• Proteins that respond to events inside the cell
are called internal regulators.
• Internal regulators allow the cell cycle to
proceed only when certain processes have
happened inside the cell.
– Cells do not enter into Mitosis until all
chromosomes have been copied
– Anaphase does not occur until all chromosomes
are lined up on metaphase plate and attached to
the mitotic spindle
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External Regulators
• Proteins that respond to events outside the
cell are called external regulators.
• External regulators direct cells to speed up or
slow down the cell cycle.
External Regulators
• Growth factors are proteins that stimulate
growth and division
After forming a single layer, cells have
stopped dividing.
Providing an additional supply of
growth factors stimulates further cell
division.
External Regulators
• Other molecules found on the surfaces of
neighboring cells can slow down or stop their
cell division
– Prevents excessive cell growth and keeps tissues in
the body from disrupting one another
• Cancer is a disorder in
which some of the
body's own cells lose
the ability to control
growth.
• Cancer cells do not
respond to the signals
that regulate the
growth of most cells.
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http://www.beliefnet.com/healthandhealing/images/Cancer_cell_division.jpg
Uncontrolled Cell Growth
Uncontrolled Cell Growth
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http://images.google.com/imgres?imgurl=http://ww
w.mmshealthyforlife.com/wpcontent/uploads/2009/04/cancer_cells_splitting.jpg&i
mgrefurl=http://www.mmshealthyforlife.com/
• Cancer cells divide uncontrollably and form masses
of cells called tumors that can damage the
surrounding tissues.
• Cancer cells may break loose from tumors and
spread throughout the body, disrupting normal
activities and causing serious medical problems or
even death.
Uncontrolled Cell Growth
• Two types of tumors
– Benign tumors
• Grow only locally
• Do not spread
• Can typically be removed
– Malignant tumors
• Grow and invade neighboring tissues
• Can break away from original tumor and spread
throughout the body (metastasis)
Uncontrolled Cell Growth
• An astonishing number of
cancer cells have a defect in
a gene called p53
• p53 is a tumor suppressing
gene found on chromosome
17
– Prevents mitosis if DNA
is damaged
– Will activate other genes
to stop cell growth or
cause cell death
http://www.hhmi.org/biointeractive/cancer/p53/01.html
Risks of Cancer
•
•
•
•
•
•
•
•
•
Tobacco (lung cancer, lip and mouth cancer)
Sunlight (UV radiation leading to skin cancer)
Ionizing radiation (X-rays)
Certain chemicals and other substances (asbestos,
benzene, certain metals, etc.)
Some viruses and bacteria (liver cancer, lymphoma,
leukemia)
Alcohol (liver cancer, breast cancer)
Poor diet, lack of physical activity, or being overweight
Growing older
Family history of cancer
www. cancer.gov
Cell Cycle Regulation
The cell cycle is believed to be controlled by proteins
called
a)
b)
c)
d)
spindles.
cyclins.
regulators.
centrosomes.
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Proteins that respond to events inside the cell are
called
a)
b)
c)
d)
internal regulators.
external regulators.
cyclins.
growth factors.
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One of the functions of internal regulators is to
a) cause the cell to stop dividing.
b) prevent anaphase from occurring until all
chromosomes are attached to the spindle.
c) trigger cancer formation.
d) undergo cell division randomly.
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One effect of an internal regulator is that a cell will
not begin mitosis until
a)
b)
c)
d)
it becomes too large.
the cell’s growth is stimulated.
it is in physical contact with other cells.
all its chromosomes have been replicated.
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One factor common to almost all cancer cells is
a)
b)
c)
d)
a lack of cyclin.
a defect in gene p53.
exposure to tobacco smoke.
exposure to radiation.
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