12 lecture gillette college biol 1010-30
DESCRIPTION
Ch 12 The Cell CycleTRANSCRIPT
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CAMPBELL
BIOLOGYReece • Urry • Cain • Wasserman • Minorsky • Jackson
© 2014 Pearson Education, Inc.
TENTH
EDITION
CAMPBELL
BIOLOGYReece • Urry • Cain • Wasserman • Minorsky • Jackson
TENTH
EDITION
12The Cell Cycle
Lecture Presentation by
Nicole Tunbridge and
Kathleen Fitzpatrick
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The Key Roles of Cell Division
The ability of organisms to produce more of their
own kind best distinguishes living things from
nonliving matter
The continuity of life is based on the reproduction
of cells, or cell division
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Figure 12.1
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Figure 12.1a
Chromosomes (blue) are moved by cell
machinery (red) during division of a rat
kangaroo cell.
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In unicellular organisms, division of one cell
reproduces the entire organism
Multicellular eukaryotes depend on cell division for
Development from a fertilized cell
Growth
Repair
Cell division is an integral part of the cell cycle,
the life of a cell from formation to its own division
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Figure 12.2
(a) Reproduction
(b) Growth and develop-
ment
(c) Tissue renewal
100 μm
50 μm
20 µm
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Concept 12.1: Most cell division results in genetically identical daughter cells
Most cell division results in daughter cells with
identical genetic information, DNA
The exception is meiosis, a special type of division
that can produce sperm and egg cells
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Cellular Organization of the Genetic Material
All the DNA in a cell constitutes the cell’s genome
A genome can consist of a single DNA molecule
(common in prokaryotic cells) or a number of DNA
molecules (common in eukaryotic cells)
DNA molecules in a cell are packaged into
chromosomes
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Eukaryotic chromosomes consist of chromatin, a
complex of DNA and protein that condenses
during cell division
Every eukaryotic species has a characteristic
number of chromosomes in each cell nucleus
Somatic cells (nonreproductive cells) have two
sets of chromosomes
Gametes (reproductive cells: sperm and eggs)
have half as many chromosomes as somatic cells
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Distribution of Chromosomes During Eukaryotic Cell Division
In preparation for cell division, DNA is replicated
and the chromosomes condense
Each duplicated chromosome has two sister
chromatids (joined copies of the original
chromosome), attached along their lengths by
cohesins
The centromere is the narrow “waist” of the
duplicated chromosome, where the two
chromatids are most closely attached
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Figure 12.4
Sister
chromatids
Centromere 0.5 μm
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During cell division, the two sister chromatids of
each duplicated chromosome separate and move
into two nuclei
Once separate, the chromatids are called
chromosomes
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Figure 12.5-1
Chromosomes
Centromere
Chromosome
arm
Chromosomal
DNA molecules
1
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Figure 12.5-2
Chromosomes
Centromere
Chromosome
arm
Chromosomal
DNA molecules
1
Chromosome
duplication
Sister
chromatids
2
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Figure 12.5-3
Chromosomes
Centromere
Chromosome
arm
Chromosomal
DNA molecules
1
Chromosome
duplication
Sister
chromatids
2
3
Separation of
sister chromatids
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Eukaryotic cell division consists of
Mitosis, the division of the genetic material in the
nucleus
Cytokinesis, the division of the cytoplasm
Gametes are produced by a variation of cell
division called meiosis
Meiosis yields nonidentical daughter cells that
have half as many chromosomes as the parent
cell
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Concept 12.2: The mitotic phase alternates with interphase in the cell cycle
In 1882, the German anatomist Walther Flemming
developed dyes to observe chromosomes during
mitosis and cytokinesis
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Phases of the Cell Cycle
The cell cycle consists of
Mitotic (M) phase (mitosis and cytokinesis)
Interphase (cell growth and copying of
chromosomes in preparation for cell division)
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Interphase (about 90% of the cell cycle) can
be divided into subphases
G1 phase (“first gap”)
S phase (“synthesis”)
G2 phase (“second gap”)
The cell grows during all three phases, but
chromosomes are duplicated only during the
S phase
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Figure 12.6
G1
G2
(DNA synthesis)
S
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Figure 12.7a
G2 of Interphase
Centrosomes
(with centriole
pairs)
Chromosomes
(duplicated,
uncondensed)
Early mitotic
spindleAster
Centromere
Fragments
of nuclear
envelope
Nonkinetochore
microtubules
Kinetochore
microtubuleKinetochoreTwo sister chromatids
of one chromosome
Plasma
membraneNuclear
envelope
Nucleolus
Prometaphase
10 μm
Prophase
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Figure 12.7b
AnaphaseMetaphase Telophase and Cytokinesis
10 μ
m
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
Daughter
chromosomes
Centrosome at
one spindle pole
Metaphase
plate
Spindle
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Figure 12.7c
Prophase
Nucleolus
G2 of Interphase
Nuclear
envelope
Plasma
membraneTwo sister chromatids
of one chromosome
Centrosomes
(with centriole
pairs)
Centrosomes
(duplicated,
uncondensed)
Early mitotic
spindleAster
Centromere
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Figure 12.7d
Metaphase
Metaphase
plate
Prometaphase
Nonkinetochore
microtubules
Fragments
of nuclear
envelope
Kinetochore Kinetochore
microtubule
SpindleCentrosome at
one spindle pole
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Figure 12.7e
Anaphase
Cleavage
furrow
Telophase and Cytokinesis
Nuclear
envelope
forming
Nucleolus
forming
Daughter
chromosomes
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BioFlix: Mitosis
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The Mitotic Spindle: A Closer Look
The mitotic spindle is a structure made of
microtubules that controls chromosome movement
during mitosis
In animal cells, assembly of spindle microtubules
begins in the centrosome, the microtubule
organizing center
The centrosome replicates during interphase,
forming two centrosomes that migrate to opposite
ends of the cell during prophase and
prometaphase
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An aster (a radial array of short microtubules)
extends from each centrosome
The spindle includes the centrosomes, the spindle
microtubules, and the asters
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During prometaphase, some spindle microtubules
attach to the kinetochores of chromosomes and
begin to move the chromosomes
Kinetochores are protein complexes associated
with centromeres
At metaphase, the chromosomes are all lined up
at the metaphase plate, a plane midway between
the spindle’s two poles
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Figure 12.8
Sister
chromatids
AsterCentrosome
Metaphase
plate
(imaginary)
Kineto-
chores
Kinetochore
microtubules
MicrotubulesOverlapping
nonkinetochore
microtubules
Chromosomes
Centrosome
1 µm 0.5 µm
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Video: Spindle Formation During Mitosis
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In anaphase the cohesins are cleaved by an
enzyme called separase
Sister chromatids separate and move along the
kinetochore microtubules toward opposite ends of
the cell
The microtubules shorten by depolymerizing at
their kinetochore ends
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Nonkinetochore microtubules from opposite poles
overlap and push against each other, elongating
the cell
In telophase, genetically identical daughter nuclei
form at opposite ends of the cell
Cytokinesis begins during anaphase or telophase
and the spindle eventually disassembles
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Cytokinesis: A Closer Look
In animal cells, cytokinesis occurs by a process
known as cleavage, forming a cleavage furrow
In plant cells, a cell plate forms during cytokinesis
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Figure 12.10
(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)
Cleavage furrow
Contractile ring of
microfilaments
Daughter cells
100 µm
1 µm
Daughter cells
New cell wallCell plate
Wall of parent cellVesicles
forming
cell plate
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Figure 12.11Nucleus
10
µm
NucleolusChromosomes
condensing Chromosomes
PrometaphaseProphaseCell plate
1 2
3 4 5Metaphase Anaphase Telophase
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Figure 12.11a
Nucleus
Nucleolus
Chromosomes
condensing
Prophase1
10 µm
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Figure 12.11b
10 µm
Chromosomes
Prometaphase2
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Figure 12.11c
3 Metaphase
10 µm
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Figure 12.11d
4 Anaphase
10 µm
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Figure 12.11e
5
Cell plate
Telophase
10 µm
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Binary Fission in Bacteria
Prokaryotes (bacteria and archaea) reproduce by
a type of cell division called binary fission
In binary fission, the chromosome replicates
(beginning at the origin of replication), and the
two daughter chromosomes actively move apart
The plasma membrane pinches inward, dividing
the cell into two
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Figure 12.12-1
Chromosome
replication
begins.
Two copies
of origin
E. coli cell
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome1
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Figure 12.12-2
Chromosome
replication
begins.
Two copies
of origin
E. coli cell
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome1
2 Origin OriginOne copy of the
origin is now at
each end of the
cell.
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Figure 12.12-3
Chromosome
replication
begins.
Two copies
of origin
E. coli cell
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome1
2 Origin OriginOne copy of the
origin is now at
each end of the
cell.
3 Replication
finishes.
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Figure 12.12-4
Chromosome
replication
begins.
Two copies
of origin
E. coli cell
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome1
2 Origin OriginOne copy of the
origin is now at
each end of the
cell.
3
Two daughter
cells result.
4
Replication
finishes.
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The Evolution of Mitosis
Since prokaryotes evolved before eukaryotes,
mitosis probably evolved from binary fission
Certain protists exhibit types of cell division that
seem intermediate between binary fission and
mitosis
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Concept 12.3: The eukaryotic cell cycle is regulated by a molecular control system
The frequency of cell division varies with the type
of cell
These differences result from regulation at the
molecular level
Cancer cells manage to escape the usual controls
on the cell cycle
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The Cell Cycle Control System
The cell cycle appears to be driven by specific
chemical signals present in the cytoplasm
Some evidence for this hypothesis comes from
experiments in which cultured mammalian cells
at different phases of the cell cycle were fused
to form a single cell with two nuclei
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The sequential events of the cell cycle are directed
by a distinct cell cycle control system, which is
similar to a clock
The cell cycle control system is regulated by both
internal and external controls
The clock has specific checkpoints where the cell
cycle stops until a go-ahead signal is received
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Figure 12.15
G1 checkpoint
G2 checkpoint
M checkpoint
G1
G2M
SControl
system
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The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases
Two types of regulatory proteins are involved in
cell cycle control: cyclins and cyclin-dependent
kinases (Cdks)
The activity of a Cdk rises and falls with changes
in concentration of its cyclin partner
MPF (maturation-promoting factor) is a cyclin-Cdk
complex that triggers a cell’s passage past the G2
checkpoint into the M phase
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Stop and Go Signs: Internal and External Signals at the Checkpoints
Many signals registered at checkpoints come from
cellular surveillance mechanisms within the cell
Checkpoints also register signals from outside
the cell
Three important checkpoints are those in G1, G2,
and M phases
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For many cells, the G1 checkpoint seems to be the
most important
If a cell receives a go-ahead signal at the G1
checkpoint, it will usually complete the S, G2, and
M phases and divide
If the cell does not receive the go-ahead signal, it
will exit the cycle, switching into a nondividing
state called the G0 phase
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Figure 12.17
G1 checkpoint
G0
G1
Without go-ahead signal,
cell enters G0.
(a) G1 checkpoint
G1
G1
G2
S
M
M checkpoint
(b) M checkpoint
Without full chromosome
attachment, stop signal is
received.
PrometaphaseAnaphase
M G2
G1
M G2
G1
With go-ahead signal,
cell continues cell cycle.
G2
checkpoint
Metaphase
With full chromosome
attachment, go-ahead signal
is received.
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Figure 12.17a
G1 checkpoint
G0
G1
Without go-ahead signal,
cell enters G0.
(a) G1 checkpoint
G1
With go-ahead signal,
cell continues cell cycle.
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Figure 12.17b
G1
M G2
G1
M G2
M
checkpoint
Without full chromosome
attachment, stop signal is
received.
PrometaphaseAnaphase
G2
checkpoint
Metaphase
With full chromosome
attachment, go-ahead signal
is received.
(b) M checkpoint
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An example of an internal signal is that cells will
not begin anaphase until all chromosomes are
properly attached to the spindle at the metaphase
plate
This mechanism assures that daughter cells have
the correct number of chromosomes
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External factors that influence cell division include
specific growth factors
Growth factors are released by certain cells and
stimulate other cells to divide
Platelet-derived growth factor (PDGF) is made by
blood cell fragments called platelets
In density-dependent inhibition, crowded cells
will stop dividing
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Figure 12.18-1
Scalpels
1
Petri
dish
A sample of
human connective
tissue is cut
up into small
pieces.
![Page 61: 12 lecture Gillette College BIOL 1010-30](https://reader033.vdocuments.net/reader033/viewer/2022060200/55981edd1a28ab83648b45f2/html5/thumbnails/61.jpg)
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Figure 12.18-2
Scalpels
1
Petri
dish
A sample of
human connective
tissue is cut
up into small
pieces.
2 Enzymes digest
the extracellular
matrix, resulting
in a suspension of
free fibroblasts.
![Page 62: 12 lecture Gillette College BIOL 1010-30](https://reader033.vdocuments.net/reader033/viewer/2022060200/55981edd1a28ab83648b45f2/html5/thumbnails/62.jpg)
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Figure 12.18-3
Scalpels
1
Petri
dish
A sample of
human connective
tissue is cut
up into small
pieces.
2 Enzymes digest
the extracellular
matrix, resulting
in a suspension of
free fibroblasts.
3 Cells are transferred
to culture vessels.4 PDGF is added
to half the
vessels.
![Page 63: 12 lecture Gillette College BIOL 1010-30](https://reader033.vdocuments.net/reader033/viewer/2022060200/55981edd1a28ab83648b45f2/html5/thumbnails/63.jpg)
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Figure 12.18-4
Scalpels
1
Petri
dish
A sample of
human connective
tissue is cut
up into small
pieces.
2 Enzymes digest
the extracellular
matrix, resulting
in a suspension of
free fibroblasts.
3 Cells are transferred
to culture vessels.4 PDGF is added
to half the
vessels.
Without PDGF With PDGF Cultured fibroblasts (SEM)
10 µ
m
![Page 64: 12 lecture Gillette College BIOL 1010-30](https://reader033.vdocuments.net/reader033/viewer/2022060200/55981edd1a28ab83648b45f2/html5/thumbnails/64.jpg)
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Most cells also exhibit anchorage dependence—
to divide, they must be attached to a substratum
Density-dependent inhibition and anchorage
dependence check the growth of cells at an
optimal density
Cancer cells exhibit neither type of regulation of
their division
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Figure 12.19
Anchorage dependence: cells
require a surface for division
Density-dependent inhibition:
cells form a single layer
Density-dependent inhibition:
cells divide to fill a gap and
then stop
(a) Normal mammalian cells (b) Cancer cells
20 µm 20 µm
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Loss of Cell Cycle Controls in Cancer Cells
Cancer cells do not respond normally to the body’s
control mechanisms
Cancer cells may not need growth factors to grow
and divide
They may make their own growth factor
They may convey a growth factor’s signal without
the presence of the growth factor
They may have an abnormal cell cycle control
system
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A normal cell is converted to a cancerous cell by a
process called transformation
Cancer cells that are not eliminated by the
immune system form tumors, masses of abnormal
cells within otherwise normal tissue
If abnormal cells remain only at the original site,
the lump is called a benign tumor
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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 additional
tumors
Localized tumors may be treated with high-energy
radiation, which damages the DNA in the cancer
cells
To treat metastatic cancers, chemotherapies that
target the cell cycle may be used
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Figure 12.20
Tumor
Glandular
tissue
A tumor grows
from a single
cancer cell.
1 2 3Cancer cells invade
neighboring tissue.
Cancer cells spread
through lymph and
blood vessels to other
parts of the body.
4 A small percentage
of cancer cells may
metastasize to
another part of the
body.
Cancer
cell
Blood
vessel
Lymph
vessel
Breast cancer cell
(colorized SEM)
Metastatic
tumor
5 µ
m
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Figure 12.20a
Tumor
Glandular
tissue
A tumor grows
from a single
cancer cell.
1 Cancer cells invade
neighboring tissue.
Cancer cells
spread through
lymph and blood
vessels to other
parts of the body.
2 3
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Figure 12.20b
3 4Cancer cells spread
through lymph and
blood vessels to other
parts of the body.
A small percentage
of cancer cells may
metastasize to
another part of the
body.
Cancer
cell
Blood
vessel
Lymph
vessel
Metastatic
tumor
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Figure 12.20c
Breast cancer cell
(colorized SEM)
5 µ
m
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Recent advances in understanding the cell cycle
and cell cycle signaling have led to advances in
cancer treatment
Coupled with the ability to sequence the DNA of
cells in a particular tumor, treatments are
becoming more “personalized”
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Figure 12.UN04