What is the leading cause of death in the U.S.? (2005)

• Heart disease: 652,091

• Cancer: 559,312 • Stroke (cerebrovascular diseases): 143,579 • Chronic lower respiratory diseases: 130,933 • Accidents (unintentional injuries): 117,809 • Diabetes: 75,119 • Alzheimer's disease: 71,599 • Influenza/Pneumonia: 63,001

• Nephritis, nephrotic syndrome, and nephrosis: 43,901 • Septicemia: 34,136

Source: CDC, National Vital Statistics Reports, Volume 56, Number 10, April 24, 2008

Leading Causes of U. S. Deaths (2006)• Heart disease: 631,636 • Cancer: 559,888 • Stroke (cerebrovascular diseases): 137,119 • Chronic lower respiratory diseases: 124,583 • Accidents (unintentional injuries): 121,599 • Diabetes: 72,449 • Alzheimer's disease: 72,432 • Influenza and Pneumonia: 56,326 • Nephritis, nephrotic syndrome, and nephrosis: 45,344 • Septicemia: 34,234

Source: CDC, National Vital Statistics Reports, Volume 57, Number 14, April 17, 2009

The Cell CycleChapter 12-

A.P. Biology

Mr. Knowles

Liberty Senior High School

• Overview: The Key Roles of Cell Division

• The continuity of life:

– is based upon the reproduction of cells, or cell division

Figure 12.1

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

Binary Fission

QuickTime™ and aGIF decompressor

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• In binary fission:– The bacterial chromosome replicates– The two daughter chromosomes actively

move apartOrigin ofreplication

E. coli cellBacterialChromosome

Cell wall

Plasma Membrane

Two copiesof origin

OriginOrigin

Chromosome replication begins.Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell.

1

Replication continues. One copy ofthe origin is now at each end of the cell.

2

Replication finishes. The plasma membrane grows inward, andnew cell wall is deposited.

3

Two daughter cells result.4

Figure 12.11

Cell Replication in Bacteria• Cell division in bacteria is controlled by the

size of the cell; volume of the cytoplasm.

• Bacteria replicate by binary fission.

• >22 enzymes copy the DNA as a circle.

• Both copies of the DNA are attached to the plasma membrane.

Replication of Bacterial Chromosome

How fast can bacteria divide?

The Evolution of Mitosis

• Since prokaryotes preceded eukaryotes by billions of years:

– It is likely that mitosis evolved from bacterial cell division

• Certain protists:

– Exhibit types of cell division that seem intermediate between binary fission and mitosis carried out by most eukaryotic cells

A hypothetical sequence for the evolution of mitosis

Most eukaryotes. In most other eukaryotes, including plants and animals, the spindle forms outside the nucleus, and the nuclear envelope breaks down during mitosis. Microtubules separate the chromosomes, and the nuclear envelope then re-forms.

Dinoflagellates. In unicellular protists called dinoflagellates, the nuclear envelope remains intact during cell division, and the chromosomes attach to the nuclear envelope. Microtubules pass through the nucleus inside cytoplasmic tunnels, reinforcing the spatial orientation of the nucleus, which then divides in a fission process reminiscent of bacterial division.

Diatoms. In another group of unicellular protists, the diatoms, the nuclear envelope also remains intact during cell division. But in these organisms, the microtubules form a spindle within the nucleus. Microtubules separate the chromosomes, and the nucleus splits into two daughter nuclei.

Prokaryotes. During binary fission, the origins of the daughter chromosomes move to opposite ends of the cell. The mechanism is not fully understood, but proteins may anchor the daughter chromosomes to specific sites on the plasma membrane.

(a)

(b)

(c)

(d)

Bacterialchromosome

Microtubules

Intact nuclear envelope

Chromosomes

Kinetochore microtubules

Intact nuclearenvelope

Kinetochore microtubules

Fragments ofnuclear envelope

Centrosome

Figure 12.12 A-D

Multicellular organisms depend on cell division for:

– Development from a fertilized cell– Growth– Repair 20 µm200 µm

(b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).

(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).

Figure 12.2 B, C

Cell Division in Eukaryotic Cells

• Eukaryotic cells are much larger.

• Also have larger genomes (the sum of an organisms’s genetic information).

• Eukaryotic DNA is organized into much more complex structures.

• Why?

The DNA molecules in a cell– Are packaged into chromosomes.

50 µm

Figure 12.3

Chromosomes of Eukaryotes

• Chromosomes are composed of chromatin - a DNA/protein complex.

• Chromatin = 40% DNA + 60% Protein.

• Every 200 nucleotides , the DNA duplex coils around a core of eight histone proteins = Nucleosome.

http://www.biostudio.com/demo_freeman_dna_coiling.htm

Polytene Chromosomes

Regions of Chromosomes are Not the Same

• Condensed portions of chromatin - Heterochromatin - are not being expressed; genes are turned off. May never be turned on.

• Other portions of chromosome are decondensed and are being actively transcribed - Euchromatin. These areas are only condensed during cell division.

Chromosome Reference Points

Karyotype

Chromosome Terminology• The two copies of each chromosome in

somatic cells - homologous chromosomes (homologues). Are these the same?

• Before cell division, each homologue replicates --> two sister chromatids that are joined at the centromere.

How Many Chromosomes are in Cells?

• Most body or somatic cells have two copies of almost identical chromosomes - diploid. Ex. Humans have 23 types of chromosomes X 2 = 46 (2n or diploid number).

• Sex cells or gametes (egg and sperm) have only one copy of each chromosome - haploid. Ex. Human sperm/egg = 23 chromosomes.

How Many Chromosomes are in Cells?

• Some somatic cells are truly unusual.

• Human liver cells have 4 copies of all chromosomes - tetraploid.

• Other cells RBC’s have no nucleus and therefore, no chromosomes.

Phases of the Cell Cycle• The cell cycle consists of

– The mitotic phase– Interphase

INTERPHASE

G1

S(DNA synthesis)

G2Cyt

okines

is

Mito

sis

MITOTIC(M) PHASE

Figure 12.5

G0

http://jnci.oxfordjournals.org/content/vol96/issue6/images/large/telomere.jpeg

Telomeres and Human Disease

•Telomere Length in Human Sperm and Aging

• Video: Scientific American Frontiers: Never Say Die, VT

571.879 SCI

Bristle Cone Pine- almost 5, 000 yrs. old

• Each duplicated chromosome:– Has two sister chromatids, which separate

during cell division0.5 µm

Chromosomeduplication(including DNA synthesis)

Centromere

Separation of sister

chromatids

Sisterchromatids

Centromeres Sister chromatids

A eukaryotic cell has multiplechromosomes, one of which is

represented here. Before duplication, each chromosome

has a single DNA molecule.

Once duplicated, a chromosomeconsists of two sister chromatids

connected at the centromere. Eachchromatid 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

• Mitosis consists of five distinct phases– Prophase– Prometaphase

G2 OF INTERPHASE PROPHASE PROMETAPHASE

Centrosomes(with centriole pairs) Chromatin

(duplicated)

Early mitoticspindle

Aster

CentromereFragmentsof nuclearenvelope

Kinetochore

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Kinetochore microtubule Figure 12.6

Nonkinetochoremicrotubules

– Metaphase– Anaphase– Telophase

Centrosome at one spindle pole

Daughter chromosomes

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Spindle

Metaphaseplate

Nucleolusforming

Cleavagefurrow

Nuclear envelopeforming

Figure 12.6

Kinetochore

EM of Spindle Fibers Attaching to Kinetochore

QuickTime™ and aGIF decompressor

are needed to see this p icture.

Kinetochores are proteins attached to the centrosome. They are used to anchor the spindle fibers to the chromosome.

The Mitotic Spindle: A Closer Look

• The mitotic spindle:– Is an apparatus of microtubules that controls

chromosome movement during mitosis.

• Some spindle microtubules:– Attach to the kinetochores of chromosomes and

move the chromosomes to the metaphase plateCentrosomeAster

Sisterchromatids

MetaphasePlate

Kinetochores

Overlappingnonkinetochoremicrotubules

Kinetochores microtubules

Centrosome

ChromosomesMicrotubules0.5 µm

1 µm

Figure 12.7

• In anaphase, sister chromatids separate:– And move along the kinetochore microtubules toward

opposite ends of the cell

EXPERIMENT

1 The microtubules of a cell in early anaphase were labeled with a fluorescent dye that glows in the microscope (yellow).

Spindlepole

Kinetochore

Figure 12.8

• Nonkinetechore 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

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are needed to see this picture.

Animal Cells have Centrioles

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are needed to see this picture.

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are needed to see this picture.

Cell Cycle

G0

Enter Mitosis!

Interphase

Prophase

Prophase and Microtubules

Metaphase

Anaphase

Telophase

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

Daughter cells

100 µm

(a) Cleavage of an animal cell (SEM)Figure 12.9 A

• In plant cells, during cytokinesis:– A cell plate forms.

Daughter cells

1 µmVesiclesforming cell plate

Wall of patent cell Cell plate

New cell wall

(b) Cell plate formation in a plant cell (SEM)Figure 12.9 B

• Mitosis in a plant cell

1

Prophase. The chromatinis condensing. The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is staring to from.

Prometaphase.We now see discretechromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelop will fragment.

Metaphase. The spindle is complete,and the chromosomes,attached to microtubulesat their kinetochores, are all at the metaphase plate.

Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomesare moving to the ends of cell as their kinetochoremicrotubles shorten.

Telophase. Daughternuclei are forming. Meanwhile, cytokinesishas started: The cellplate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell.

2 3 4 5

Nucleus

Nucleolus

ChromosomeChromatinecondensing

Figure 12.10

Terms for Bio Demo - 10 pts.• Using pp. 222-3, draw and label:

• G1, S, G2, M, Cytokinesis, G0

• M = Prophase, Prometaphase, Metaphase, Anaphase, Telophase

• 2 pairs of Homologous Chromosomes, Centromere, Nuclear Membrane, Kinetochores, Asters, Cleavage Furrow, Nonkinetochore and Kinetochore Spindles (Microtubules), Centrosome

Due Monday• Concept Map of the topic Mitosis

Concepts: Interphase, Prophase, Metaphase, Anaphase, Telophase, Sister Chromatids, Centromere, Kinetochore, Plant Cell, Animal Cell, Spindle fibers, Aster, Centrioles, Cytokinesis, Cleavage Furrow, Cell Plate,

Mitosis in a Blood Lilly

How Mitosis and the Cell Cycle Relate!

Cytokinesis Mutations

Cyd Mutations Close Up!

Plant vs. Animal Mitosis

Plant Cells• Lack centrioles• No aster• Assemble membrane

components in the interior- cell plate

• Deposits cellulose- new cell wall.

Animal Cells

• Use centrioles

• Centrioles develop an aster

• Actin filaments constrict the cell -cleavage furrow.

Mitosis in a Newt

What’s the overall goal of mitosis?

What happens when cells divide out of control?

• Concept 12.3: 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

Cell Cycle Control• Internal clocks are not flexible.

• Eukaryotic cells use Check Points- enzymes that survey conditions of the cell and act as “go/no go” switches.

• Regulated by feedback from the cell.

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

Figure 12.14

Control system

G2 checkpoint

M checkpoint

G1 checkpoint

G1

S

G2M

• The clock has specific checkpoints:– Where the cell cycle stops until a go-ahead signal is received

G1 checkpoint

G1G1

G0

(a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues      on in the cell cycle.

(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.

Figure 12.15 A, B

Three Principal Checkpoints

• G1 Checkpoint (also called START)- end of G1/beginning of S- decision to replicate DNA.

• Surveys cell size and environmental conditions.

G1 CheckpointReplicate DNA Yes

Cell Size?

Favorable

Conditions? No

Grow or GO

G2 Checkpoint

• Occurs at the end of G2 and triggers mitosis.

G2 Checkpoint

DNA Mitosis

Replicated? Yes

Cell Size?

Growth No

Conditions?

Pause

M Check Point

• Occurs at metaphase, triggers exit from mitosis and beginning of G1.

M Check Point

Are All Anaphase

Chromosomes Yes

Aligned?

No

Pause

Checkpoints Regulated by Enzymes• Cyclins- proteins that appear and

disappear at different points in the cell cycle.

• Cyclin-Dependent Kinases- (Cdk’s)- enzymes that phosphorylate other enzymes and proteins. Not active w/o cyclins.

The activity of cyclins and Cdksfluctuates during the cell cycle

During G1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled.

5

During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G1 phase.

4

Accumulated cyclin moleculescombine with recycled Cdk mol-ecules, producing enough molecules of MPF to pass the G2 checkpoint and initiate the events of mitosis.

2

Synthesis of cyclin begins in late S phase and continues through G2. Because cyclin is protected from degradation during this stage, it accumulates.

1

Cdk

CdkG2

checkpoint

CyclinMPF

Cyclin is degraded

DegradedCyclin

G 1

G 2

S

M

G1G1 S G2 G2SM M

MPF activity

Cyclin

Time

(a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

(b) Molecular mechanisms that help regulate the cell cycle

MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase.

3

Figure 12.16 A, B

M

Regulating the Cell Cycle

Example: Figure 12.16

• At the G2 checkpoint, use

Cdk + cyclin -----> MPF (Mitosis Promoting Factor)

Evidence for Cytoplasmic Signals• Molecules present in the cytoplasm

– Regulate progress through the cell cycleIn each experiment, cultured mammalian cells at two different phases of the cell cycle were induced to fuse.

When a cell in the M phase was fused with a cell in G1, the G1 cell immediately began mitosis— a spindle formed and chromatin condensed, even though the chromosome had not been duplicated.

EXPERIMENTS

RESULTS

CONCLUSION The results of fusing cells at two different phases of the cell cycle suggest that molecules present in the cytoplasm of cells in the S or M phase control the progression of phases.

When a cell in the S phase was fused with a cell in G1, the G1 cellimmediately entered the S phase—DNA was synthesized.

S

S S M M

MG1 G1

Experiment 1 Experiment 2

Figure 12.13 A, B

Controlling the Cell Cycle• Growth Factors. 100 + so far, many

work at G1 checkpoint; bind to surface receptors of cells. Ex. PDGF.

• Contact Inhibition. Normal cells stop growing when they make contact with other cells; use surface receptors.

Signal Transduction and the Cell Cycle

• Growth factors:– Stimulate other cells to divide

EXPERIMENT

A sample of connective tissue was cut up into small pieces.

Enzymes were used to digest the extracellular matrix,resulting in a suspension of free fibroblast cells.

Cells were transferred to sterile culture vessels containing a basic growth medium consisting of glucose, amino acids, salts, and antibiotics (as a precaution against bacterial growth). PDGF was added to half the vessels. The culture vessels were incubated at 37°C.

3

2

1

Petriplate

Without PDGF

With PDGF

Scalpels

Figure 12.17

• In density-dependent inhibition (contact inhibition):– Crowded cells stop dividing

• Most animal cells exhibit anchorage dependence– In which they must be attached to a substratum to divide

Cells anchor to dish surface anddivide (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. The availability of nutrients, growth factors, and a substratum for attachment limits cell density to a single layer.

(a)

25 µm

Figure 12.18 A

• Cancer cells– Exhibit neither density-dependent inhibition

nor anchorage dependence.

25 µm

Cancer cells do not exhibitanchorage dependence or density-dependent inhibition.

Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells.

(b)

Figure 12.18 B

Devil Facial Tumor Disease (DFTD)

A Transmissable Cancer – a neuroendocrine tumor spread by feeding, cuts and scratches.

• Malignant tumors invade surrounding tissues and can metastasize– Exporting cancer cells to other parts of the body where

they may form secondary tumors

Cancer cells invade neighboring tissue.

2A small percentage of cancer cells may survive and establish a new tumor in another part of the body.

4Cancer cells spread through lymph and blood vessels to other parts of the body.

3

A tumor grows from a single cancer cell.

1

Tumor

Glandulartissue

Cancer cell

Bloodvessel

Lymphvessel

MetastaticTumor

Figure 12.19

How do Growth Factors Work?

• G. F.’s allow passage through G1 checkpoint by causing more cyclins to be formed.

• Some genes normally stimulate cell division- protooncogenes. (myc, fos, jun, ras) Ch. 19.

When Protooncogenes Go Bad!• Mutations in protooncogenes or their

regulation lead to oncogenes – genes that promote uncontrolled cell division and MAY lead to tumor formation.

• Ex. Growth Factor, HER-2 and Breast Cancer

HER-2 Receptor as an Oncogene

Herceptin – a treatment

Figure 19.12a

(a) Cell cycle–stimulating pathway.

This pathway is triggered by a growthfactor that binds to its receptor in theplasma membrane. The signal is relayed to a G protein called Ras. Like all G proteins, Rasis active when GTP is bound to it. Ras passesthe signal to a series of protein kinases.The last kinase activates a transcriptionactivator that turns on one or more genes for proteins that stimulate the cell cycle. If amutation makes Ras or any other pathway component abnormally active, excessive celldivision and cancer may result.

1

2

4

3

5

GTP

Ras

Ras

GTP

HyperactiveRas protein(product ofoncogene)issues signalson its own

NUCLEUS

Gene expression

Protein thatstimulatesthe cell cycle

P

P

P

P

MUTATION

P

DNA

P

• The Ras protein, encoded by the ras protoncogene– Is a G protein that relays a signal from a growth factor

receptor on the plasma membrane to a cascade of protein kinases

2 Receptor

Transcriptionfactor (activator)

5

G protein3

Protein kinases(phosphorylationcascade)

4

1 Growth factor

p53 Tumor SuppressorDelays cycle at G1

until DNA repaired.

Is DNA

Damaged? If irrepairable,causes apoptosis(programmed cell death).

If p53 is not functioning, leads to

mutations-->cancer.

p53

• The p53 gene encodes a tumor-suppressor protein– That is a specific transcription factor that promotes

the synthesis of cell cycle–inhibiting proteins

Figure 19.12b

UVlight

DNA

Defective ormissingtranscriptionfactor, such asp53, cannotactivatetranscription

MUTATION

Protein thatinhibitsthe cell cycle

pathway, DNA damage is an intracellularsignal that is passed via protein kinasesand leads to activation of p53. Activatedp53 promotes transcription of the gene for aprotein that inhibits the cell cycle. Theresulting suppression of cell division ensuresthat the damaged DNA is not replicated.Mutations causing deficiencies in anypathway component can contribute to thedevelopment of cancer.

(b) Cell cycle–inhibiting pathway. In this

1

3

2

Protein kinases2

3Activeformof p53

DNA damagein genome

1

Protein Kinases

p21 binds to CDK

• Mutations that knock out the p53 gene– Can lead to excessive cell growth and cancer

Figure 19.12c

EFFECTS OF MUTATIONS

Proteinoverexpressed

Cell cycleoverstimulated Increased cell

division

Cell cycle notinhibited

Protein absent

Effects of mutations. Increased cell division, possibly leading to cancer, can result if the cell cycle is overstimulated, as in (a), or not inhibited when it normally would be, as in (b).

(c)

Controlling Cell Growth• The case of retinoblastoma (Rb).• Some genes normally inhibit cell

division- tumor suppressor genes.

• Example: In GO, Rb protein is dephosphorylated and binds to the Myc protein, preventing its promoting of cell division.

Two Types of Cell Division Control

• Positive Controls- like growth factors, protoncogenes stimulate cell division.

• Negative Controls- like tumor suppressors, contact inhibition prevent cell division. Ex. p53, BRCA1 and 2 (Breast Cancer, early onset)

Mutations in Cell Division Control

• Mutations in protoncogenes – tend to be dominant – only one defective copy needed to lead to cancer.

• Mutations in tumor suppressors – tend to be recessive- can still suppress cell division with only one good copy of the gene- both must be defective to develop cancer.

• Fig. 19.13: A multistep model for the development of colorectal cancer - about a dozen mutations in genes needed ( at least one oncogene and many tumor suppressor mutations are needed)

Figure 19.13

Colon

Colon wall

Normal colonepithelial cells

Small benigngrowth (polyp)

Larger benigngrowth (adenoma)

Malignant tumor(carcinoma)

2 Activation ofras oncogene

3 Loss oftumor-suppressorgene DCC

4 Loss oftumor-suppressorgene p53

5 Additionalmutations

1 Loss of tumor-suppressorgene APC (orother)

How could dwarfism prevent cancer?

• The story of Laron Syndrome (receptor-deficient form of pituitary dwarfism)- http://www.youtube.com/watch?v=oDOF9miyDEg&safety_mode=true&persist_safety_mode=1&safe=active

Controlling the Cell Cycle-17.6 lb tumor!

For tumors to grow beyond the size of a pinhead…

• They must develop their own blood supply.

• Angiogenesis – blood vessel creation – tumor cells secrete growth factors of their own to attract capillaries into themselves.

Ovarian TeratomaHair

A Fun Review of the Cell Cycle

Mitosis and Cancer

Video: Nova- Cancer Warrior

Artificial Uterus

Sakata, M., et al. (1997)