biology in focus - chapter 9

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

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



Figure 9.1

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



Figure 9.2

(a) Reproduction

100 m

(c) Tissue renewal

(b) Growth anddevelopment

200 m

20 m


Figure 9.2a

(a) Reproduction

100 m


Figure 9.2b

(b) Growth and development

200 m


Figure 9.2c

(c) Tissue renewal

20 m

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


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



Figure 9.3

Eukaryotic chromosomes20 m

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


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



Figure 9.4

Centromere 0.5 m

Sisterchromatids

During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei

Once separate, the chromatids are called chromosomes



Figure 9.5-1

Centromere

ChromosomalDNA moleculesChromosomes

Chromosomearm

1


Figure 9.5-2

Centromere

Sisterchromatids


Chromosomearm

Chromosome duplication

1

2


Figure 9.5-3

Centromere

Sisterchromatids

Separation of sisterchromatids


Chromosomearm

Chromosome duplication

1

3

2

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


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


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


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



Figure 9.6

Cytokinesis

Mitosis

S(DNA synthesis)G1

G2

Mitosis is conventionally divided into five phases Prophase Prometaphase Metaphase Anaphase Telophase

Cytokinesis overlaps the latter stages of mitosis



Video: Animal Mitosis

Video: Microtubules Mitosis

Animation: Mitosis

Video: Microtubules Anaphase

Video: Nuclear Envelope


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


Figure 9.7b

Metaphase Anaphase Telophase and Cytokinesis

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

Spindle Centrosome atone spindle pole

Daughterchromosomes

10

m

Metaphaseplate


Figure 9.7c

Centrosomes(with centriolepairs)

G2 of Interphase ProphaseChromosomes(duplicated,uncondensed)

Early mitoticspindle

CentromereAster

NucleolusPlasmamembrane Two sister chromatids of

one chromosomeNuclearenvelope


Figure 9.7d

PrometaphaseFragmentsof nuclearenvelope

Nonkinetochoremicrotubules


Kinetochore Spindle Centrosome atone spindle pole

Metaphaseplate

Metaphase


Figure 9.7e

Anaphase Telophase and Cytokinesis

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

Daughterchromosomes


Figure 9.7f

G2 of Interphase

10

m


Figure 9.7g

Prophase

10

m


Figure 9.7h

Prometaphase

10

m


Figure 9.7i

10

m

Metaphase


Figure 9.7j

Anaphase

10

m


Figure 9.7k

Telophase and Cytokinesis

10

m

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


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


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


Video: Mitosis Spindle


Figure 9.8

Metaphase plate(imaginary)

Chromosomes

Aster

Kinetochoremicrotubules

Kineto-chores

Sisterchromatids

1 m

Centrosome

Overlappingnonkinetochoremicrotubules

Centrosome

Microtubules

0.5 m


Figure 9.8a

Chromosomes

1 m

Centrosome

Microtubules


Figure 9.8b

Kinetochoremicrotubules

Kinetochores

0.5 m

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



Figure 9.9

KinetochoreExperiment

Spindlepole

Results

Kinetochore

Conclusion

Mark

Tubulinsubunits

Chromosome

Motorprotein

Chromosomemovement

Microtubule


Figure 9.9a

KinetochoreExperiment

Spindlepole

Mark


Figure 9.9b

Results

Kinetochore

Conclusion

Tubulinsubunits

Chromosome

Motorprotein

Chromosomemovement

Microtubule

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


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


Animation: Cytokinesis

Video: Cytokinesis and Myosin


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)


Figure 9.10a

(a) Cleavage of an animal cell (SEM)

Contractile ring ofmicrofilaments

Cleavage furrow

Daughter cells

100 m


Figure 9.10aa

Cleavage furrow 100 m


Figure 9.10b

New cell wall

Daughter cells

Cell plate

Wall of parentcell


1 m

(b) Cell plate formation in a plant cell (TEM)


Figure 9.10ba

Wall of parentcell


1 m


Figure 9.11

10 m

Nucleus

Telophase

NucleolusChromosomescondensing Chromosomes

PrometaphaseCell plate

Prophase

AnaphaseMetaphase

1 2

3 4 5


Figure 9.11a

10 m

NucleusNucleolus

Chromosomescondensing

Prophase1


Figure 9.11b

10 m2 Prometaphase

Chromosomes


Figure 9.11c

10 m3 Metaphase


Figure 9.11d

10 m4 Anaphase


Figure 9.11e

10 m5 Telophase

Cell plate

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



Figure 9.12-1

1

Origin ofreplication

Two copiesof origin

Bacterialchromosome

Plasmamembrane

Cell wall

E. coli cellChromosomereplicationbegins.


Figure 9.12-2

1


Two copiesof origin

Bacterialchromosome

Plasmamembrane

Cell wall

E. coli cell

Origin Origin

Chromosomereplicationbegins.

2 One copy of theorigin is now ateach end of thecell.


Figure 9.12-3

1


Two copiesof origin

Bacterialchromosome

Plasmamembrane

Cell wall

E. coli cell

Origin Origin


2

3

One copy of theorigin is now ateach end of thecell.

Replicationfinishes.


Figure 9.12-4

1


Two copiesof origin

Bacterialchromosome

Plasmamembrane

Cell wall

E. coli cell

Origin Origin


2

3

4

One copy of theorigin is now ateach end of thecell.

Replicationfinishes.

Two daughtercells result.

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



Figure 9.13 Chromosomes

Intact nuclearenvelope

Microtubules


Intact nuclearenvelope

(a) Dinoflagellates

(b) Diatoms and some yeasts

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


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



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.

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



Figure 9.15

M checkpoint

S

M

G1

G2

G1 checkpoint

G2 checkpoint

Controlsystem

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



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.


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


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.

The cell cycle is regulated by a set of regulatory proteins and protein complexes including kinases and proteins called cyclins


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


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



Figure 9.17-1

1 A sample ofhuman connectivetissue is cutup into smallpieces.

Petridish

Scalpels


Figure 9.17-2


2 Enzymes digestthe extracellularmatrix, resultingin a suspension offree fibroblasts.

Petridish

Scalpels


Figure 9.17-3


2

3

Enzymes digestthe extracellularmatrix, resultingin a suspension offree fibroblasts.

Cells are transferredto culture vessels.

Petridish

Scalpels

4 PDGF is added tohalf the vessels.


Figure 9.17-4


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


Figure 9.17a

Cultured fibroblasts(SEM) 10 m

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



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


Figure 9.18a

20 m

(a) Normal mammalian cells


Figure 9.18b

(b) Cancer cells

20 m

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


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



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


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


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


Figure 9.19c

Breast cancer cell(colorized SEM)

5 m

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



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


Figure 9.UN02

SG1

G2Mitosis

Telophase andCytokinesis

Cytokinesis

MITOTIC (M) PHASE

AnaphaseMetaphase

Prometaphase

Prophase


Figure 9.UN03

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