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Chapter 12
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cell Division in Organisms
• Unicellular organisms
• Multicellular organisms
– Development from a fertilized cell
– Growth
– Repair
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 12-2
100 µm
Reproduction
200 µm
Growth and development
20 µm
Tissue renewal
Concept 12.1: Cell division results in genetically
identical daughter cells
• Daughter Cells
– duplicate their genetic material
– genome
– chromosomes
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Eukaryotic Cell Classification
• Somatic (nonreproductive)
• Gametes (reproductive cells: sperm and eggs)
• Chromatin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 12-3
25 µm
Distribution of Chromosomes During Cell Division
• Duplicated chromosomes have 2 sister chromatids
0.5 µm
• Centromere
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Separation
of sister
chromatids
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Centromeres
Sister chromatids
• Eukaryotic cell division consists of:
– Mitosis
– Cytokinesis
• Meiosis produces gametes
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Phases of the Cell Cycle
• The cell cycle consists of
– Mitotic (M) phase
– Interphase
• Interphase subphases:
– G1 phase (“first gap”)
– S phase (“synthesis”)
– G2 phase (“second gap”)
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LE 12-5
INTERPHASE
G1
S
(DNA synthesis)
G2
• Mitosis is conventionally divided into five phases:
– Prophase
– Prometaphase
– Metaphase
– Anaphase
– Telophase
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LE 12-6ca
G2 OF INTERPHASE
PROPHASE
PROMETAPHASE
LE 12-6da
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Video: Animal Mitosis
Video: Sea Urchin (time lapse)
Animation: Mitosis (All Phases)
Animation: Mitosis Overview
Animation: Late Interphase
Animation: Prophase
Animation: Prometaphase
Animation: Metaphase
Animation: Anaphase
Animation: Telophase
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The Mitotic Spindle: A Closer Look
• Mitotic spindle
– Microtubules
• Centrosome, the microtubule organizing center
– Two Centrosomes
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• Aster - extends from each centrosome
• Kinetochores
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LE 12-7
Aster
Microtubules
Sister
chromatids
Chromosomes
Centrosome
Metaphase
plate
Kinetochores
Overlapping
nonkinetochore
microtubules
Centrosome
1 µm
Kinetochore
microtubules
0.5 µm
• Microtubules shorten by depolymerizing
Chromosome
movement
Microtubule
Motor
protein
Chromosome
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Kinetochore
Tubulin
subunits
• Nonkinetochore microtubules
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Cytokinesis: A Closer Look
• Cytokinesis
– Animals
• cleavage, forming a cleavage furrow
– Plants
• cell plate forms
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Animation: Cytokinesis
LE 12-9a
100 µm
Cleavage furrow
Contractile ring of
microfilaments
Daughter cells
Cleavage of an animal cell (SEM)
LE 12-9b
Vesicles
forming
cell plate
Wall of
parent cell
Cell plate
1 µm
New cell wall
Daughter cells
Cell plate formation in a plant cell (TEM)
LE 12-10
Nucleus
Nucleolus
Chromatin
condensing
Prophase. The
chromatin is condensing.
The nucleolus is beginning
to disappear.
Although not yet visible in
the micrograph, the mitotic
spindle is starting to form.
Chromosomes
Prometaphase. We
now see discrete
chromosomes; each
consists of two identical sister
chromatids. Later
in prometaphase, the
nuclear envelope will fragment.
Cell plate
Metaphase. The spindle is
complete, and the
chromosomes, attached to
microtubules at their
kinetochores, are all at
the metaphase plate.
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends of
the cell as their
kinetochore microtubules shorten.
10 µm
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell plate,
which will divide the
cytoplasm in two, is
growing toward the
perimeter of the parent
cell.
Binary Fission
• Binary Fission
• Origin of Replication
Origin of
replication
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LE 12-11_1
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Two copies
of origin
Bacterial
chromosome
LE 12-11_2
Cell wall
Origin of
replication
Plasma
membrane
E. coli cell
Bacterial
chromosome
Two copies
of origin
Origin
Origin
LE 12-11_3
Cell wall
Origin of
replication
E. coli cell
Plasma
membrane
Bacterial
chromosome
Two copies
of origin
Origin
Two daughter
cells result.
Origin
The Evolution of Mitosis
Bacterial
chromosome
Prokaryotes
• Since prokaryotes
evolved before
eukaryotes, mitosis
probably evolved
from binary fission
Chromosomes
Microtubules
Intact nuclear
envelope
Dinoflagellates
Kinetochore
microtubules
• Intermediate types:
Intact nuclear
envelope
Diatoms
Kinetochore
microtubules
Centrosome
Fragments of
nuclear envelope
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Most eukaryotes
Concept 12.3: The cell cycle is regulated by a
molecular control system
• The cell cycle appears to be driven by specific
chemical signals present in the cytoplasm
Experiment 1
Experiment 2
S
G1
M
G1
S
S
M
M
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The Cell Cycle Control System
• Has specific checkpoints where the cell cycle
stops until a go-ahead signal is received
G1 checkpoint
Control
system
G1
M
G2
M checkpoint
G checkpoint
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2
S
• If a cell receives a go-ahead signal at the G1
checkpoint, it will usually complete the cycle.
• G0 phase
G0
G1 checkpoint
G1
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G1
The Cell Cycle Clock: Cyclins and
Cyclin-Dependent Kinases
• Two types of regulatory proteins are involved in
cell cycle control:
– Cyclins
– Cyclin-dependent kinases (Cdks)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 12-16a
M
G1
S
G2
M
G1
S
G2
M
MPF activity
Cyclin
Time
Fluctuation of MPF activity and cyclin concentration
during the cell cycle
LE 12-16b
Cdk
Degraded
cyclin
G2
Cdk
checkpoint
Cyclin is
degraded
MPF
Cyclin
Molecular mechanisms that help regulate the cell cycle
Stop and Go Signs: Internal and External Signals at
the Checkpoints
• Internal signal
– kinetochores not attached to spindle
microtubules send a molecular signal that
delays anaphase
• External signals
– growth factors
• platelet-derived growth factor (PDGF)
human fibroblast cells
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LE 12-17
Scalpels
Petri
plate
Without PDGF
With PDGF
Without PDGF
With PDGF
10 mm
• External signals
– density-dependent inhibition
• Anchorage dependence
– seen in animal cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 12-18a
Cells anchor to dish surface and
divide (anchorage dependence).
When cells have formed a complete
single layer, they stop dividing
(density-dependent inhibition).
If some cells are scraped away, the
remaining cells divide to fill the gap and
then stop (density-dependent inhibition).
Normal mammalian cells
25 µm
• Cancer cells exhibit neither density-dependent
inhibition nor anchorage dependence
Cancer cells do not exhibit
anchorage dependence
or density-dependent inhibition.
25 µm
Cancer cells
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Loss of Cell Cycle Controls in Cancer Cells
• Tumors
– Benign tumor
– Malignant tumors
• metastasize
Lymph
vessel
Tumor
Blood
vessel
Glandular
tissue
Cancer cell
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Metastatic
tumor