Biology in Focus - Chapter 9
Transcript of Biology in Focus - Chapter 9
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CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
9The Cell Cycle
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Overview: 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 9.1
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In unicellular organisms, division of one cell reproduces the entire organism
Cell division enables multicellular eukaryotes to develop from a single cell and, once fully grown, to renew, repair, or replace cells as needed
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 9.2
(a) Reproduction
100 m
(c) Tissue renewal
(b) Growth anddevelopment
200 m
20 m
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Figure 9.2a
(a) Reproduction
100 m
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Figure 9.2b
(b) Growth and development
200 m
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Figure 9.2c
(c) Tissue renewal
20 m
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Concept 9.1: Most cell division results in genetically identical daughter cells
Most cell division results in the distribution of identical genetic material—DNA—to two daughter cells
DNA is passed from one generation of cells to the next with remarkable fidelity
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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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Figure 9.3
Eukaryotic chromosomes20 m
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Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein
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 one set of chromosomes
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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 identical copies of the original chromosome
The centromere is where the two chromatids are most closely attached
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Figure 9.4
Centromere 0.5 m
Sisterchromatids
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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 9.5-1
Centromere
ChromosomalDNA moleculesChromosomes
Chromosomearm
1
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Figure 9.5-2
Centromere
Sisterchromatids
ChromosomalDNA moleculesChromosomes
Chromosomearm
Chromosome duplication
1
2
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Figure 9.5-3
Centromere
Sisterchromatids
Separation of sisterchromatids
ChromosomalDNA moleculesChromosomes
Chromosomearm
Chromosome duplication
1
3
2
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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 only one set of chromosomes, half as many as the parent cell
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Concept 9.2: 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, including mitosis and cytokinesis Interphase, including 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 9.6
Cytokinesis
Mitosis
S(DNA synthesis)G1
G2
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Mitosis is conventionally divided into five phases Prophase Prometaphase Metaphase Anaphase Telophase
Cytokinesis overlaps the latter stages of mitosis
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Video: Animal Mitosis
Video: Microtubules Mitosis
Animation: Mitosis
Video: Microtubules Anaphase
Video: Nuclear Envelope
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Figure 9.7a
Centrosomes(with centriolepairs)
G2 of Interphase Prophase PrometaphaseChromosomes(duplicated,uncondensed)
Early mitoticspindle
CentromereAster
Fragmentsof nuclearenvelope
Nonkinetochoremicrotubules
Kinetochoremicrotubule
KinetochoreNucleolusPlasmamembrane Two sister chromatids of
one chromosomeNuclearenvelope
10
m
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Figure 9.7b
Metaphase Anaphase Telophase and Cytokinesis
Cleavagefurrow
Nucleolusforming
Nuclearenvelopeforming
Spindle Centrosome atone spindle pole
Daughterchromosomes
10
m
Metaphaseplate
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Figure 9.7c
Centrosomes(with centriolepairs)
G2 of Interphase ProphaseChromosomes(duplicated,uncondensed)
Early mitoticspindle
CentromereAster
NucleolusPlasmamembrane Two sister chromatids of
one chromosomeNuclearenvelope
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Figure 9.7d
PrometaphaseFragmentsof nuclearenvelope
Nonkinetochoremicrotubules
Kinetochoremicrotubule
Kinetochore Spindle Centrosome atone spindle pole
Metaphaseplate
Metaphase
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Figure 9.7e
Anaphase Telophase and Cytokinesis
Cleavagefurrow
Nucleolusforming
Nuclearenvelopeforming
Daughterchromosomes
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Figure 9.7f
G2 of Interphase
10
m
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Figure 9.7g
Prophase
10
m
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Figure 9.7h
Prometaphase
10
m
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Figure 9.7i
10
m
Metaphase
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Figure 9.7j
Anaphase
10
m
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Figure 9.7k
Telophase and Cytokinesis
10
m
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The Mitotic Spindle: A Closer Look
The mitotic spindle is a structure made of microtubules and associated proteins
It controls chromosome movement during mitosis In animal cells, assembly of spindle microtubules
begins in the centrosome, the microtubule organizing center
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The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase
An aster (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 that assemble on sections of DNA at centromeres
At metaphase, the centromeres of all the chromosomes are at the metaphase plate, an imaginary structure at the midway point between the spindle’s two poles
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Video: Mitosis Spindle
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Figure 9.8
Metaphase plate(imaginary)
Chromosomes
Aster
Kinetochoremicrotubules
Kineto-chores
Sisterchromatids
1 m
Centrosome
Overlappingnonkinetochoremicrotubules
Centrosome
Microtubules
0.5 m
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Figure 9.8a
Chromosomes
1 m
Centrosome
Microtubules
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Figure 9.8b
Kinetochoremicrotubules
Kinetochores
0.5 m
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In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell
The microtubules shorten by depolymerizing at their kinetochore ends
Chromosomes are also “reeled in” by motor proteins at spindle poles, and microtubules depolymerize after they pass by the motor proteins
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Figure 9.9
KinetochoreExperiment
Spindlepole
Results
Kinetochore
Conclusion
Mark
Tubulinsubunits
Chromosome
Motorprotein
Chromosomemovement
Microtubule
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Figure 9.9a
KinetochoreExperiment
Spindlepole
Mark
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Figure 9.9b
Results
Kinetochore
Conclusion
Tubulinsubunits
Chromosome
Motorprotein
Chromosomemovement
Microtubule
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Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell
At the end of anaphase, duplicate groups of chromosomes have arrived at opposite ends of the elongated parent 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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Animation: Cytokinesis
Video: Cytokinesis and Myosin
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Figure 9.10
(a) Cleavage of an animal cell (SEM)
New cell wall
Contractile ring ofmicrofilaments
Cleavage furrow
Daughter cells
Daughter cells
Cell plate
Wall of parentcell
Vesiclesformingcell plate
100 m1 m
(b) Cell plate formation in a plant cell (TEM)
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Figure 9.10a
(a) Cleavage of an animal cell (SEM)
Contractile ring ofmicrofilaments
Cleavage furrow
Daughter cells
100 m
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Figure 9.10aa
Cleavage furrow 100 m
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Figure 9.10b
New cell wall
Daughter cells
Cell plate
Wall of parentcell
Vesiclesformingcell plate
1 m
(b) Cell plate formation in a plant cell (TEM)
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Figure 9.10ba
Wall of parentcell
Vesiclesformingcell plate
1 m
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Figure 9.11
10 m
Nucleus
Telophase
NucleolusChromosomescondensing Chromosomes
PrometaphaseCell plate
Prophase
AnaphaseMetaphase
1 2
3 4 5
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Figure 9.11a
10 m
NucleusNucleolus
Chromosomescondensing
Prophase1
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Figure 9.11b
10 m2 Prometaphase
Chromosomes
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Figure 9.11c
10 m3 Metaphase
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Figure 9.11d
10 m4 Anaphase
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Figure 9.11e
10 m5 Telophase
Cell plate
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Binary Fission in Bacteria
Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission
In E. coli, the single chromosome replicates, beginning at the origin of replication
The two daughter chromosomes actively move apart while the cell elongates
The plasma membrane pinches inward, dividing the cell into two
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Figure 9.12-1
1
Origin ofreplication
Two copiesof origin
Bacterialchromosome
Plasmamembrane
Cell wall
E. coli cellChromosomereplicationbegins.
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Figure 9.12-2
1
Origin ofreplication
Two copiesof origin
Bacterialchromosome
Plasmamembrane
Cell wall
E. coli cell
Origin Origin
Chromosomereplicationbegins.
2 One copy of theorigin is now ateach end of thecell.
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Figure 9.12-3
1
Origin ofreplication
Two copiesof origin
Bacterialchromosome
Plasmamembrane
Cell wall
E. coli cell
Origin Origin
Chromosomereplicationbegins.
2
3
One copy of theorigin is now ateach end of thecell.
Replicationfinishes.
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Figure 9.12-4
1
Origin ofreplication
Two copiesof origin
Bacterialchromosome
Plasmamembrane
Cell wall
E. coli cell
Origin Origin
Chromosomereplicationbegins.
2
3
4
One copy of theorigin is now ateach end of thecell.
Replicationfinishes.
Two daughtercells result.
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The Evolution of Mitosis
Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission
Certain protists (dinoflagellates, diatoms, and some yeasts) exhibit types of cell division that seem intermediate between binary fission and mitosis
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Figure 9.13 Chromosomes
Intact nuclearenvelope
Microtubules
Kinetochoremicrotubule
Intact nuclearenvelope
(a) Dinoflagellates
(b) Diatoms and some yeasts
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Concept 9.3: 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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Evidence for Cytoplasmic Signals
The cell cycle is driven by specific signaling molecules present in the cytoplasm
Some evidence for this hypothesis comes from experiments with cultured mammalian cells
Cells at different phases of the cell cycle were fused to form a single cell with two nuclei at different stages
Cytoplasmic signals from one of the cells could cause the nucleus from the second cell to enter the “wrong” stage of the cell cycle
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Figure 9.14
G1 nucleusimmediately enteredS phase and DNAwas synthesized.
ExperimentExperiment 1 Experiment 2
Results
S
SS
MG1
MM
G1
G1 nucleus beganmitosis withoutchromosomeduplication.
Conclusion Molecules present in the cytoplasmcontrol the progression to S and M phases.
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Checkpoints of 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 timing device of a washing machine
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 9.15
M checkpoint
S
M
G1
G2
G1 checkpoint
G2 checkpoint
Controlsystem
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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 9.16
M checkpoint
G1
G1 checkpoint
M
G1
G2
Without go-ahead signal,cell enters G0.
G0
With go-ahead signal,cell continues cell cycle.
(a) G1 checkpoint
Prometaphase
G1
M G2
Without full chromosomeattachment, stop signal isreceived.(b) M checkpoint
S
G1
M
G1
G2
G2 checkpoint
MetaphaseAnaphase
With full chromosomeattachment, go-ahead signalis received.
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Figure 9.16a
G1
G1 checkpoint
Without go-ahead signal,cell enters G0.
G0
With go-ahead signal,cell continues cell cycle.
(a) G1 checkpoint
G1
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Figure 9.16b
M checkpoint
M
G1
G2
PrometaphaseWithout full chromosomeattachment, stop signal isreceived.(b) M checkpoint
M
G1
G2
G2 checkpoint
MetaphaseAnaphase
With full chromosomeattachment, go-ahead signalis received.
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The cell cycle is regulated by a set of regulatory proteins and protein complexes including kinases and proteins called cyclins
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An example of an internal signal occurs at the M phase checkpoint
In this case, anaphase does not begin if any kinetochores remain unattached to spindle microtubules
Attachment of all of the kinetochores activates a regulatory complex, which then activates the enzyme separase
Separase allows sister chromatids to separate, triggering the onset of anaphase
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Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
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Figure 9.17-1
1 A sample ofhuman connectivetissue is cutup into smallpieces.
Petridish
Scalpels
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Figure 9.17-2
1 A sample ofhuman connectivetissue is cutup into smallpieces.
2 Enzymes digestthe extracellularmatrix, resultingin a suspension offree fibroblasts.
Petridish
Scalpels
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Figure 9.17-3
1 A sample ofhuman connectivetissue is cutup into smallpieces.
2
3
Enzymes digestthe extracellularmatrix, resultingin a suspension offree fibroblasts.
Cells are transferredto culture vessels.
Petridish
Scalpels
4 PDGF is added tohalf the vessels.
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Figure 9.17-4
1 A sample ofhuman connectivetissue is cutup into smallpieces.
2
34
Enzymes digestthe extracellularmatrix, resultingin a suspension offree fibroblasts.
Cells are transferredto culture vessels. PDGF is added to
half the vessels.
Without PDGF With PDGF Cultured fibroblasts(SEM) 10 m
Petridish
Scalpels
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Figure 9.17a
Cultured fibroblasts(SEM) 10 m
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Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing
Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide
Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence
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Figure 9.18
Anchorage dependence: cellsrequire a surface for division
20 m
Density-dependent inhibition:cells divide to fill a gap andthen stop
Density-dependent inhibition:cells form a single layer
20 m
(a) Normal mammalian cells (b) Cancer cells
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Figure 9.18a
20 m
(a) Normal mammalian cells
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Figure 9.18b
(b) Cancer cells
20 m
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Loss of Cell Cycle Controls in Cancer Cells
Cancer cells do not respond to signals that normally regulate the cell cycle
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
Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors
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Figure 9.19
1 A tumor growsfrom a singlecancer cell.
Cancer cellsinvadeneighboringtissue.
Cancer cells spreadthrough lymph andblood vessels toother parts of the body.
A small percentageof cancer cells maymetastasize toanother part of the body.
Breast cancer cell(colorized SEM)
Lymphvessel
Bloodvessel
Cancercell
Metastatictumor
Glandulartissue
Tumor
5 m
2 3 4
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Figure 9.19a
A tumor growsfrom a singlecancer cell.
Cancer cellsinvadeneighboringtissue.
Cancer cells spreadthrough lymph andblood vessels toother parts of the body.
Glandulartissue
Tumor
1 2 3
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Figure 9.19b
43 Cancer cells spreadthrough lymph andblood vessels toother parts of the body.
A small percentageof cancer cells maymetastasize toanother part of the body.
Lymphvessel
Bloodvessel
Cancercell
Metastatictumor
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Figure 9.19c
Breast cancer cell(colorized SEM)
5 m
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Recent advances in understanding the cell cycle and cell cycle signaling have led to advances in cancer treatment
Medical treatments for cancer are becoming more “personalized” to an individual patient’s tumor
One of the big lessons in cancer research is how complex cancer is
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Figure 9.UN01
Control Treated A B CA B C
Amount of fluorescence per cell (fluorescence units)
Num
ber o
f cel
ls
200
160
120
80
40
0 200 400 600 0
0 200 400 600
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Figure 9.UN02
SG1
G2Mitosis
Telophase andCytokinesis
Cytokinesis
MITOTIC (M) PHASE
AnaphaseMetaphase
Prometaphase
Prophase
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Figure 9.UN03