Lecture Notebook to accompany Principles of Life · PDF fileLecture Notebook to accompany ......

Sinauer Associates, Inc. W. H. Freeman and Company

Lecture Notebook to accompany

Copyright © 2012 Sinauer Associates, Inc. Cover photograph © Fred Bavendam/Minden Pictures.

This document may not be modified or distributed (either electronically or on paper) without the permission of the publisher, with the following exception: Individual users may enter their own notes into this document and may print it for their own personal use.

© 2012 Sinauer Associates, Inc.

The Cell Cycle and Cell Division 7

2

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POL Sadava Sinauer AssociatesMorales Studio Figure 07.01 Date 07-20-10

(A) Reproduction

(C) Regeneration

(B) Growth

These yeast cells divide by budding.

Cell division contributes to the regeneration of a lizard’s tail.

Cell division contributes to the growth of this root.

2 µm

FIGURE 7.1 The Importance of Cell Division (Page 125)

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<---protective root cap

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<----region of cell division

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<---region of cell elongation

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(meristem) cells are dividing but increasing in size much.


Chapter 7 | The Cell Cycle and Cell Division 3

FIGURE 7.2 Asexual Reproduction on a Large Scale (Page 125)


In the haplontic life cycle, the mature organism is haploid and the zygote is the only diploid stage.

In alternation of generations, the organism passes through haploid and diploid stages that are both multicellular.

In the diplontic life cycle, the organism is diploid and the gametes are the only haploid stage.

Sporophyte(2n)

Zygote (2n)

GametesMale (n) Female (n)

Spore (n)

Gametophyte(n)

Mature organism (n)


Matureorganism (2n)

Zygote (2n)


Bread mold (Rhizopus stolonifer) (haploid organism)

Fern (Asplenium trichomanes) (diploid sporophyte)

African fish eagle (Haliaeetus vocifer) (diploid organism)

DIPLOID (2n)

DIPLOID (2n)

HAPLOID (n) HAPLOID (n)

DIPLOID (2n)

HAPLOID (n)

Spores (n)

Zygote (2n)

Meiosis

Meiosis

Meiosis

Fertilization

Fertilization

Fertilization

50 µm

FIGURE 7.3 All Sexual Life Cycles Involve Fertilization and Meiosis (Page 126)

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Aspen trees arose from asexual reproduction are genetically identical. These trees are clones. Aspens can reproduce sexually but in this case all the trees are males.

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Know the 3 different life cycles. In sexual reproduction, haploid(n) cells or organisms alternate with diploid (2n) cells.

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Know the differences of haploid and diploid. What is gametophyte and sporophyte?




Plasma membrane

Chromosome

ori

DNA replication begins at the origin of replication at the center of the cell.

1

The chromosomal DNA replicates as the cell grows.

2

Cytokinesis is complete; two new cells are formed.

4

The daughter DNAs separate, led by the region including ori. The cell begins to divide.

3

FIGURE 7.4 Prokaryotic Cell Division (Page 128)

POL HillisSinauer AssociatesMorales Studio Figure 07.05 Date 07-08-10

In the M phase cell, the DNA and proteins in each chromosome form highly compact structures.

During interphase, DNA is replicated. Only a tiny portion of one chromosome is shown.

In an interphase nucleus, chromosomesare threadlike structures dispersed throughout the nucleus.

Centromere

Sisterchromatids

G1

M

G2

S

Interphase

5 µm

0.5 µm

FIGURE 7.5 The Phases of the Eukaryotic Cell Cycle (Page 129)

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Genetically identical offspring. Asexual reproduction.

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Know the structure of a chromosome

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Phases if interphase 1. G1- longer phase 2. S-DNA replicates; centrosomes duplicate 3. G2-preps for mitosis



POL Sadava Sinauer AssociatesMorales Studio Figure Intext #1 Date 07-21-10

Polar microtubules extend from each pole of the spindle.

Kinetochore microtubules attach to the kinetochores and to the spindle poles.

Polarmicrotubule

Centrosome

Centriole

Kinetochore

Kinetochoremicrotubule

IN-TEXT ART (Page 129)

POL Sadava Sinauer AssociatesMorales Studio Figure 07.06 LEFT Date 07-21-10

During the S phase of interphase, the nucleus replicates its DNA and centrosomes.

1 The chromatin coils and supercoils, becoming more and more compact and condensing into visible chromosomes. The chromosomes consist of identical, paired sister chromatids. Centrosomes move to opposite poles.

2 The nuclear envelope breaks down. Kinetochore microtubules appear and connect the kinetochores to the poles.

3

Interphase Prophase Prometaphase

Nuclear envelope Kinetochore

microtubules

Kinetochore

Nuclear envelope

Nucleus Nucleolus

Centrosomes

Developingspindle

Chromatids ofchromosome

FIGURE 7.6 The Phases of Mitosis (Pages 130 and 131)

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Kinetechore on the centromere of each chromatid is important for chromosome movement

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The centrosome is known as the central body. Each centrosome has a pair of centrioles(hollow tube formed by nine triplets of chromosomes. The pair of centrosomes separate and move to opposite poles. The position of the centrosomes will determine how the cell divides.

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2 types of microtubules in the spindle 1. Polar microtubules- run from one pole to another 2. Kinetochore microtubules- form later and attach to the kinetochore of each chromosome.



POL Sadava Sinauer AssociatesMorales Studio Figure 07.06RIGHT Date 07-21-10

The centromere/kinetochore complexes become aligned in a plane, which is often at the cell’s equator.

4 The paired sister chromatids separate, and the new daughter chromosomes begin to move toward the poles.

5 The daughter chromosomes reach the poles. As telophase concludes, the nuclear envelopes and nucleoli re-form, the chromatin decondenses, and, after cytokinesis, the daughter cells enter interphase once again.

6

Metaphase Anaphase Telophase

Equatorial(metaphase)plate

Daughterchromosomes

FIGURE 7.6 The Phases of Mitosis (continued)

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Results: 2 nuclei that are genetically identical to each other.




The contractile ring has completely separated the cytoplasms of these two daughter cells, although their surfaces remain in contact.

This row of vesicles will fuse to form a cell plate between the cell above and the cell below.

50 µm10 µm

(A) (B)

Contractilering

Cell plate

FIGURE 7.7 Cytokinesis Differs in Animal and Plant Cells (Page 132)


Nuclear division occurs during mitosis.

DNA is replicated during S phase.

Cells that do not divide are usually arrestedin the G1 phase.

Transition from G1 to S is regulated at the restriction point.

Cell division—cytokinesis—occurs at theend of the M phase.

Mitosis(M)

G1

Restriction point (R)

G2

DNA synthesis(S)

Interphase

FIGURE 7.8 The Eukaryotic Cell Cycle (Page 133)

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Cytokinesis differs in plant and animal cells

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Precise distribution of chromosomes is ensured by mitosis . However, organelles such as ribosomes, mitochondria and chloroplasts are not usually equally distributed.

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Cell reproduction is controlled to maintain form and function. Mammals produce a variety of growth factors that stimulate cell division and differentiation. Ex: platelets in our blood secrete growth factors that stimulate nearby skin cells to divide and heal the wound. The 4 stages of the cell cycle, G1, S, G2 and M is tightly regulated. G1-S transitions (restriction point- R) usually means the cell will proceed with the rest of the cycle.




HYPOTHESIS

CONCLUSION

INVESTIGATION

Go to yourBioPortal.com for original citations, discussions,and relevant links for all INVESTIGATION figures.

The S phase cell produces a substance that diffuses to theG1 nucleus and activates DNA replication.

A cell in S phase contains an activatorof DNA replication.

METHOD

FIGURE 7.9 Regulation of the Cell Cycle Nuclei in G1 do not undergo DNA replication, but nuclei in S phase do. To determine if there is some signal in the S cells that stimulates G1 cells to replicate their DNA, cells in the G1 and S phases were fused together, creating cells with both G1 and S properties.

RESULTS

ANALYZE THE DATA

The experiment used mammalian cells undergoing the cell cyclesynchronously. Radioactive labeling and microscopy were used to

determine which nuclei were synthesizing DNA.Here are counts of the cell nuclei that were labeled:

A. What were the percentages of cells in S phase in each of the three experiments? B. What does this mean in terms of control of the cell cycle?

Cells are fused in polyethylene glycol.

Both nuclei in the fused cell enter S phase.

In S phase

The fused cell has two nuclei

In G1 phase

DNAreplication

DNAreplication

Cells with labeledType of cells nuclei/total cells

Unfused G1: 6/300Unfused S: 435/500Fused G1 and S cells: 17*/19

*Both nuclei labeled

(Page 133)




Cdk is present, but without cyclin it is not active.

Cyclin synthesisbegins during G1.

Cyclin binds to Cdk,which becomes active.

Cyclin breaks down.Cdk is

inactive.

Mitosis(M)

G1G2

DNA synthesis(S)

CyclinCdk

Cdk

CdkCdk

Cdk

Cdk

Cdk

Restriction point (R)

FIGURE 7.10 Cyclins Are Transient in the Cell Cycle (Page 134)

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Molecular activators revealed by the cell fusion experiments turned out to be protein kinases. Enzymes that are common in signal transduction. Class of protein kinases involved in cell cycle regulation is Cdk's. tThey bind to the protein cyclin. This binding changes the shape and is allosteric regulation. Cyclins are synthesized in response to various molecular signals, including growth factors. growth factor--> cyclin synthesis-->Cdk activation---> cycle events The S phase of the cycle is dependent on cyclin and Cdk. RB phosphorylation acts as an inhibitor of the cell cycle at the R point. To begin S phase the cell must overcome this block. Cyclin-Cdk comes in and catalyzes the addition of the phosphate to RB. The cell proceeds proceeds with the cell cycle. The main thing to know is that the cell cycle is dependent on the cyclin Cdk relationship.



POL Sadava Sinauer AssociatesMorales Studio Figure 07.12 ALTERNATE LAYOUT Date 07-21-10

No pairing of homologous chromosomes.

1

Individual chromosomes align at the equatorial plate.

2

Centromeres separate. Sister chromatids separate during anaphase, becoming daughter chromosomes.

3

Pairing and crossing over of homologs.

1

Homologous pairs align at the equatorial plate.

2

Centromeres do not separate; sisterchromatids remaintogether duringanaphase; homologs separate; DNA does not replicate before prophase II.

3

Mitosis is a mechanism for constancy:The parent nucleus produces two genetically identical daughter nuclei.

At the end of telophase I, the two homologs are segregated from one another.

Meiosis II produces four haploid daughter cells that are genetically distinct. Meiosis is thus a mechanism for generating diversity.

Pairs ofhomologs

Prophase

Metaphase

Anaphase

MITOSIS MEIOSIS

Parent cell (2n) Parent cell (2n)

Prophase I

Metaphase I

Anaphase I

Two daughter cells (each 2n)

2n 2n2n 2n

n n n nn n n nFour daughter cells (each n)

Telophase I

FIGURE 7.11 Mitosis and Meiosis: A Comparison (Page 135)



POL Sadava Sinauer AssociatesMorales Studio Figure 07.11LEFT Date 07-21-10

The chromatin begins to condense following interphase.

1

The chromosomes condense again,following a brief interphase (interkinesis)in which DNA does not replicate.

7 8 9

Synapsis aligns homologs, and chromosomes condense further.

2 The chromosomes continue to coil and shorten. The chiasmata reflect crossing over, the exchange of genetic material between nonsister chromatids in a homologous pair. In prometa-phase the nuclear envelope breaks down.

3

The centromeres of the paired chromatids line up across the equatorial plates of each cell.

The chromatids finally separate, becoming chromosomes in their own right, and arepulled to opposite poles. Because of crossingover and independent assortment, each new cell will have a different genetic makeup.

Early prophase I Mid-prophase I Late prophase I–Prometaphase

Prophase II Metaphase II Anaphase II

Pairs ofhomologs

TetradChiasma

Centrosomes

Equatorial plate

MEIOSIS I

MEIOSIS II

FIGURE 7.12 Meiosis: Generating Haploid Cells (Pages 136 and 137)



POL Sadava Sinauer AssociatesMorales Studio Figure 07.11RIGHT Date 07-21-10

The homologous pairs line up on the equatorial (metaphase) plate.

4

The chromosomes gather into nuclei, and the cells divide.

10 11

The homologous chromosomes (each with two chromatids) move to opposite poles of the cell.

5 The chromosomes gather into nuclei, and the original cell divides.

6

Each of the four cells has a nucleus with a haploid number of chromosomes.

Metaphase I Anaphase I Telophase I

Telophase II Products

Equatorial plate

FIGURE 7.12 Meiosis: Generating Haploid Cells (continued)

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Particulars of Meiosis: Nucleus divides twice DNA is replicated only once 4 haploid cells are produced, not genetically identical. Crossing over of chromatids can happen along with independent assortment.



POL HillisSinauer AssociatesMorales Studio Figure Intext 07.03 Date 08-03-10

Chiasmata

Centromeres

Homologouschromosomes


POL HillisSinauer AssociatesMorales Studio Figure Intext 07.13 Date 08-03-10

During prophase I, homologous chromosomes, each with a pair of sister chromatids, line up to form a tetrad.

Adjacent chromatids of different homologs break and rejoin. Because there is still sister chromatid cohesion, a chiasma forms.

The chiasma is resolved. Recombinant chromatids contain genetic material from different homologs.

Homologouschromosomes

Chiasma

Recombinant chromatids

Sisterchromatids

FIGURE 7.13 Crossing Over Forms Genetically Diverse Chromosomes (Page 139)

POL HillisSinauer AssociatesMorales Studio Figure In text 07.04 Date 07-08-10

abl

bcr

#9

#22


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The chiasmata reflects crossing over, the exchange of genetic material between non-sister chromatids.

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The chiasma is the point where the genetic material is exchanged. The four chromatids form a tetrad. This happens during Prophase I and MetaphaseI Crossing over results in recombinant chromatids and it increases genetic variating by reshuffling genetic information Mitosis usually last about an hour or two but meiosis is much longer. In human males the cells in the testis that undergo meiosis take about a week for prophase I and 1 month for the entire cycle. In females, prophase begins before a woman's birth and the cycle ends decades later. Independent assortment is also a source of genetic diversity. It is chance of which member of the homlogous pair goes to which daughter cell at anaphase I. Read p. 138-139 about independent assortment.

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tetrad

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Read about translocation p. 140 Common in mitotic cells During crossing over in meiosis I, chromatids from homologous chromosome pairs break and rejoin. Translocation can cause defects in the genetic information. Read on p. 140 about translocation and the effects of white blood cells.




Inactive caspase changes its structure to become active.

A cell in apoptosis displays extensive membrane blebbing.

A normal whiteblood cell.

2

External signals can bind to a receptor protein.

Caspase hydrolyzes nuclear proteins, nucleosomes, etc.,resulting in apoptosis.

3

1a

Internal signals can bind to mitochondria, releasing other signals.

1b(B)(A)

FIGURE 7.14 Apoptosis: Programmed Cell Death (Page 141)


There are few copies of the growth factor receptor HER2 on normal breast cells.

In breast cancer, changes in DNA may result in many receptors, making the cell sensitive to growth factor stimulation.

In normal cervical cells, RBprotein acts to inhibit cellcycle initiation.

In cervical cancer, a virus makes a protein that inactivates RB, so thecell cycle proceeds uncontrolled.

(A)

(B)

HER2

RB

cell cycle proceeds uncontrolled.

XXX

FIGURE 7.15 Molecular Changes Regulate the Cell Cycle in Cancer Cells (Page 142)

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Understand these terms that relate to cell death. Necrosis- when cells are damaged by mechanical means or toxins, or they could be starved of oxygen. Apoptosis- genetically programmed series of events that cause a cell to die. Reasons? 1. The cell is no longer needed by the organism. Find an example on p. 141 2. The longer the cells live the more chance they have of being exposed to toxins or pathogens. Plant cells can undergo apoptosis if cells are infected with a fungus or disease.

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***cell death is control by signals which can come from inside or outside the cell. Both internal and external signals are called caspases.

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1. Oncogene-proteins are positive regulators of the cell cycle in cancer cells. They become mutated and overactive; stimulate the cancer cells to divide more often. Tumor suppressors are inactive in cancer cells. Read about the HPV hijack system. How does it fit into the protein binding site? What kind of cancer does this cause?

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