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Mitosis
The Cell Cycle
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: The Key Roles of Cell Division
• Life continues because of the reproduction of
cells, or cell division
Figure 12.1
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Unicellular organisms
– Reproduce by cell division
100 µm
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
Figure 12.2 A
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Multicellular organisms depend on cell division for
– Development from a fertilized cell
– Growth
– Repair
200 µm
Figure 12.2 B, C
(b) Growth and development.
This micrograph shows a
sand dollar embryo shortly
after the fertilized egg divided,
forming two cells (LM).
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20 µm
(c) Tissue renewal. These dividing
bone marrow cells (arrow) will
give rise to new blood cells (LM).
Cell division results in genetically identical
daughter cells
Cells duplicate their genetic material
– Before they divide, ensuring that each
daughter cell receives an exact copy of the
genetic material, DNA.
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Cellular Organization of the Genetic Material
• A cell’s endowment of DNA, its genetic
information
– Is called its genome
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The DNA molecules in a cell
– Are packaged into chromosomes
Figure 12.3
50 µm
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Eukaryotic chromosomes
• In animals
– Somatic (body) cells have two sets of
chromosomes
– Gametes (sexual cells) have one set of
chromosomes
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Chromatin
• A combination of DNA and protein that condenses
and becomes visible during cell division
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Distribution of Chromosomes During Cell Division
• In preparation for cell division
– DNA is replicated and the chromosomes
condense
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Each duplicated chromosome
– Has two sister chromatids, which separate
during cell division
0.5 µm
A eukaryotic cell has multiple
chromosomes, one of which is
represented here. Before
duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosome
consists of two sister chromatids
connected at the centromere. Each
chromatid contains a copy of the
DNA molecule.
Mechanical processes separate
the sister chromatids into two
chromosomes and distribute
them to two daughter cells.
Figure 12.4
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Chromosome
duplication
(including DNA
synthesis)
Centromere
Separation
of sister
chromatids
Centromeres
Sister
chromatids
Sister chromatids
Eukaryotic cell division consists of
– Mitosis, the division of the nucleus
– Cytokinesis, the division of the cytoplasm
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Phases of the Cell Cycle
• The cell cycle consists of
– The mitotic phase
– Interphase
INTERPHASE
G1
S
(DNA synthesis)
G2
Figure 12.5
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Interphase can be divided into subphases
– G1 phase
– S phase
– G2 phase
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The mitotic phase
– Is made up of mitosis and cytokinesis
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Mitosis consists of five distinct phases
– Prophase
– Prometaphase
G2 OF
INTERPHASE
Centrosomes
Chromatin
(with centriole pairs)
(duplicated)
Figure 12.6
Nucleolus
Nuclear
Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
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PROMETAPHASE
Fragments
Kinetochore
of nuclear
envelope
Nonkinetochore
microtubules
Kinetochore
microtubule
– Metaphase
– Anaphase
– Telophase
METAPHASE
ANAPHASE
Metaphase
plate
Figure 12.6
Spindle
Centrosome at Daughter
one spindle pole chromosomes
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TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
The Spindle: A Closer Look
• The spindle
– Is an apparatus of microtubules that controls
chromosome movement during mitosis
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Some spindle microtubules
–
Attach to the kinetochores of chromosomes and move the
chromosomes to the metaphase plate
Aster
Sister
chromatids
Centrosome
Metaphase
Plate
Kinetochores
Overlapping
nonkinetochore
microtubules
Kinetochores
microtubules
Microtubules
Figure 12.7
0.5 µm
Chromosomes
Centrosome
1 µm
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In anaphase, sister chromatids separate
– And move along the kinetochore microtubules
toward opposite ends of the cell
Kinetochore
Spindle
pole
Figure 12.8
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telophase
– Genetically identical daughter nuclei form at
opposite ends of the cell
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Cytokinesis: A Closer Look
• In animal cells
– Cytokinesis occurs by a process known as
cleavage, forming a cleavage furrow
Cleavage furrow
Contractile ring of
microfilaments
Figure 12.9 A
100 µm
Daughter cells
(a) Cleavage of an animal cell (SEM)
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In plant cells, during cytokinesis
– A cell plate forms
Vesicles
forming
cell plate
Figure 12.9 B
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
(b) Cell plate formation in a plant cell (SEM)
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Mitosis in a plant cell
Chromatine
Nucleus
Nucleolus condensing
Chromosome
Metaphase. The
2 Prometaphase.
3
1 Prophase.
spindle is complete, 4
The chromatin
We now see discrete
and the chromosomes,
is condensing.
chromosomes; each
attached to microtubules
The nucleolus is
consists of two
at their kinetochores,
beginning to
identical sister
are all at the metaphase
disappear.
chromatids. Later
plate.
Although not
in prometaphase, the
yet visible
nuclear envelop will
in the micrograph,
fragment.
the mitotic spindle is
staring to from.
Figure 12.10
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Anaphase. The
5
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends
of cell as their
kinetochore
microtubles shorten.
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will
divided the cytoplasm
in two, is growing
toward the perimeter
of the parent cell.
Binary Fission
• Prokaryotes (bacteria)
– Reproduce by a type of cell division called
binary fission
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In binary fission
– The bacterial chromosome replicates
– The two daughter chromosomes actively move apart
Origin of
replication
Cell wall
E. coli cell
1 Chromosome replication begins.
Soon thereafter, one copy of the
origin moves rapidly toward the
other end of the cell.
2 Replication continues. One copy of
the origin is now at each end of
the cell.
3 Replication finishes. The plasma
membrane grows inward, and
new cell wall is deposited.
Figure 12.11 4 Two daughter cells result.
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Two copies
of origin
Origin
Plasma
Membrane
Bacterial
Chromosome
Origin
The Evolution of Mitosis
• Since prokaryotes came before eukaryotes by
billions of years
– It is likely that mitosis evolved from bacterial
cell division
• Certain protists
– Exhibit types of cell division that seem in
between binary fission and mitosis carried out
by most eukaryotic cells
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The cell cycle is regulated by a molecular control
system
• The frequency of cell division
– Varies with the type of cell
• These cell cycle differences
– Result from regulation at the molecular level
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The Cell Cycle Control System
• The sequential events of the cell cycle
– Are directed by a distinct cell cycle control
system, which is similar to a clock
G1 checkpoint
Control
system
G1
M
G2
M checkpoint
Figure 12.14
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G2 checkpoint
S
• The clock has specific checkpoints
– Where the cell cycle stops until a go-ahead signal is
received
G0
G1 checkpoint
G1
Figure 12.15 A, B
(a) If a cell receives a go-ahead signal at
the G1 checkpoint, the cell continues
on in the cell cycle.
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G1
(b) If a cell does not receive a go-ahead
signal at the G1checkpoint, the cell
exits the cell cycle and goes into G0, a
nondividing state.
Loss of Cell Cycle Controls in Cancer Cells
• Cancer cells
– Do not respond normally to the body’s control
mechanisms
– Form tumors
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Malignant tumors invade surrounding tissues and
can metastasize
– Exporting cancer cells to other parts of the
body where they may form secondary tumors
Lymph
vessel
Tumor
Blood
vessel
Glandular
tissue
1 A tumor grows from a
single cancer cell.
Cancer cell
2 Cancer cells invade
neighboring tissue.
Figure 12.19
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3 Cancer cells spread
through lymph and
blood vessels to
other parts of the body.
Metastatic
Tumor
4 A small percentage of
cancer cells may survive
and establish a new tumor
in another part of the body.
Life Span of Human Body Cells:
• Cell type
Length of time
Red blood
120 days
Lymphocytes
Over one year
Other white
10 hours
Platelets
10 days
Bone
25-30 years
Brain
Lifetime
Colon
3-4 days
Skin
19-34 days
Spermatozoa
2-3 days
Stomach
2 days
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