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10-2 Cell Division
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Cell Division
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
Chromosomes
Genetic information is passed from one generation to
the next on chromosomes.
Before cell division, each chromosome is duplicated,
or copied.
Chromosomes
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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.
Sister chromatids
Centromere
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Chromosomes
When the cell divides, the chromatids
separate.
Each new cell gets one chromatid.
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The Cell Cycle
Cell Cycle
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.
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The Cell Cycle
During the cell cycle:
• a cell grows
• prepares for division
• divides to form two daughter cells, each of which
begins the cycle again
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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
Events of the Cell Cycle
During G1, the cell
– increases in size
– synthesizes new proteins and organelles
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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.
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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
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Events of the Cell Cycle
Cell Cycle
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Mitosis
Mitosis
Biologists divide the events of mitosis into four
phases: (PMAT)
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
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Mitosis
Mitosis
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Section 10-2
Mitosis
Prophase
Spindle
forming
Prophase
Chromosomes
(paired
chromatids)
Centromere
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Mitosis Spindle
forming
Prophase
Prophase is the first and
longest phase of mitosis.
The centrioles separate
and take up positions on
opposite sides of the
nucleus.
Centromere
Chromosomes
(paired
chromatids)
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Mitosis Spindle
forming
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.
Centromere
Chromosomes
(paired
chromatids)
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Mitosis Spindle
forming
Chromatin condenses
into chromosomes.
The centrioles separate
and a spindle begins to
form.
The nuclear envelope
breaks down.
Centromere
Chromosomes
(paired
chromatids)
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Mitosis
Metaphase
Centriole
Spindle
Centriole
Metaphase
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Mitosis
Centriole
Metaphase
The second phase of
mitosis is metaphase.
The chromosomes line up
across the center of the
cell.
Microtubules connect the
centromere of each
chromosome to the
poles of the spindle.
Spindle
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Mitosis
Anaphase
Individual
chromosomes
Anaphase
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Mitosis
Anaphase
Individual
chromosomes
phase
Anaphase is the third
of mitosis.
The sister chromatids
separate into individual
chromosomes.
The chromosomes continue
to move until they have
separated into two
groups.
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Mitosis
Telophase
Nuclear
envelope
reforming
Telophase
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Mitosis
Telophase
Telophase is the fourth
and final phase of
mitosis.
Chromosomes gather at
opposite ends of the
cell and lose their
distinct shape.
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Mitosis
A new nuclear envelope
forms around each cluster
of chromosomes.
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Cytokinesis
Cytokinesis
Cytokinesis
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Cytokinesis
During cytokinesis, the
cytoplasm pinches in
half.
Each daughter cell has an
identical set of
duplicate chromosomes
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Cytokinesis in Plants
In plants, a structure known as the cell plate forms midway
between the divided nuclei.
Cell plate
Cell wall
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The series of events that cells go through as they
grow and divide is called
•
•
•
•
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
•
•
•
•
prophase.
metaphase.
anaphase.
telophase.
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Cytokinesis usually occurs
•
•
•
•
at the same time as telophase.
after telophase.
during interphase.
during anaphase
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DNA replication takes place during the
•
•
•
•
S phase of the cell cycle.
G1 phase of the cell cycle.
G2 phase of the cell cycle.
M phase of the cell cycle.
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During mitosis, “sister” chromatids separate from
one another during
•
•
•
•
telophase.
interphase.
anaphase.
metaphase.
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10-3 Regulating the Cell Cycle
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Controls on Cell Division
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
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Cell Cycle Regulators
How is the cell cycle regulated?
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Cell Cycle Regulators
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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Cell Cycle Regulators
Cyclins were discovered during a similar experiment to this one.
A sample of cytoplasm
is removed from a cell
in mitosis.
The sample is injected
into a second cell in
G2 of interphase.
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As result, the second
cell enters mitosis.
Cell Cycle Regulators
Internal Regulators
Internal regulators allow the cell cycle to proceed only
when certain processes have happened inside the cell.
Example: p53 Gene that regulates the passage into
mitosis
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Cell Cycle Regulators
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.
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Uncontrolled Cell Growth
Uncontrolled Cell Growth
Cancer is a disorder in which some of the body's
own cells lose the ability to control growth.
How are cancer cells different from other cells?
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Uncontrolled Cell Growth
Cancer cells do not respond to the signals that
regulate the growth of most cells.
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Uncontrolled Cell Growth
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.
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The cell cycle is believed to be controlled by proteins
called
•
•
•
•
spindles.
cyclins.
regulators.
centrosomes.
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Proteins that respond to events inside the cell are
called
•
•
•
•
internal regulators.
external regulators.
cyclins.
growth factors.
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103
Once a multicellular organism reaches adult size, the
cells in its body
• stop dividing.
• grow and divide at different rates, depending on the
type.
• have the same life span between cell divisions.
• undergo cell division randomly.
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103
One effect of an internal regulator is that a cell will
not begin mitosis until
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•
•
•
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 lack of cyclin.
a defect in gene p53.
exposure to tobacco smoke.
exposure to radiation.
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