Cellular Reproduction: Cells from Cells CH. 8 Ms. Haut Copyright © 2003 Pearson Education, Inc....

Cellular Reproduction: Cells from Cells

Ms. Haut

Onion Root Tip Lab ActivityOnion Root Tip Lab Activity

http://www.biology.arizona.edu/cell_bio/http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/Cell_cycle.htmlactivities/cell_cycle/Cell_cycle.html

Connections between Cell Division and Reproduction

Asexual reproductionindividual parent divides into two genetically

identical daughter cells

Sexual reproductiontwo parents contribute genetic material to the

offspring which is genetically unique

1. Replacement of lost or damaged cells

2. Growth—multicellular organisms grow and develop from single cell (fertilize egg)

3. Cell Reproduction

Roles of Cell DivsionRoles of Cell Divsion

Cell replacement (seen here in skin)

Deadcells

Figure 8.11B

Dividingcells

Epidermis, the outer layer of the skin

Dermis

ProkaryotesProkaryotes

Genes usually carried on a single circular DNA molecule

DNA has a few proteins and is attached to the plasma membrane at one point

DNA not bounded by membrane (nucleoid region)

Cells divide by binary fission

http://www.karlloren.com/biopsy/images/TEM-Fission_rod.jpg

Binary Fission Before dividing, an exact copy of

the chromosome is made The attachment point divides so the

2 new chromosomes are attached at separate parts of the membrane

The cell elongates and a new plasma membrane is added and the attachment points move apart

The plasma membrane and new cell wall pinch through the cell, separating the 2 chromosomes into two new, identical cells

Eukaryotic Cell Cycle and Mitosis

Genome—a cell’s total hereditary endowment of DNAGenome is specific to species

• Human DNA extends about 3 meters, so how is it possible to copy all of it and ensure cells get even distrubution?

-DNA molecules are packaged into linear chromosomes which are more manageable

Eukaryotic ChromosomesEukaryotic Chromosomes

Are made of chromatin, a combination of DNA and protein molecules.

Are not visible in a cell until cell division occurs. The DNA in a cell is

packed into an elaborate, multilevel system of coiling and folding.

Figure 8.5

Before a cell starts dividing, the chromosomes are duplicated

This process produces sister chromatids

Centromere

Sister chromatids

Figure 8.4B

When the cell divides, the sister chromatids separate Two daughter cells are

produced Each has a complete and

identical set of chromosomes

Chromosome NumberChromosome Number

Human somatic cells contain 46 chromosomes (23 pairs)

Human reproductive cells, gametes—sperm and egg cells—have 23 chromosomes Normal karyotype

http://members.aol.com/chrominfo/images/bigktype.gif

Mitotic Cell Cycle

In a dividing cell, the mitotic phase (M) phase alternates with interphase, a growth period. Mitotic phase—usually

the shortest part of cell cycle

Interphase—accounts for –90% of the cycle

Figure 8.7

Interphase Subphases

G1 phase (first gap)—cell grows by producing proteins and cytoplasmic organelles

S phase (synthesis of DNA)—cell continues to grow as in G1 phase, while duplicating chromosomes

G2 phase (second gap)—grows more as it completes preparations for cell division

Mitosis

ProphaseMetaphaseAnaphaseTelophase

G2 of Interphase

Nucleus well-defined and bounded by nuclear envelope

Contains one or more nucleoli. 2 centrosomes (with centriole

pairs) visible Chromosomes duplicated

Still seen as chromatin (DNA + protein)

No individual chromosomes seen

Figure 8.8.1

Prophase

Chromatin fibers become more tightly coiled, condensing into discrete chromosomes

Nucleoli disappear Chromosomes appear as 2

identical sister chromatids joined together by centromere

Mitotic spindle begins to form (made of microtubules), radiating from centrosomes

Centrosomes move to opposite poles

Figure 8.8.2

Prophase

Nuclear envelope fragments-disintegrates

Microtubules of spindle extend from poles and invade nucleus and interact with chromosomes

Kinetochore forms on chromatids

Some spindle fibers connect with kinetochores; some attach to opposite pole Figure 8.8.2

Metaphase

Centrosomes at opposite poles of cell

Chromosomes convene on the metaphase plate

Centromeres of all chromosomes are aligned with one another, and sister chromatids straddle metaphase plate

Mitotic spindle completely

formed

Figure 8.8.2

Anaphase

Paired centromeres of each chromosome separate

Each chromatid is now considered a full-fledged chromosome and move to opposite poles as kinetochore microtubules shorten

Figure 8.8.3

Chromosome MovementChromosome Movement

Chromosomes move Chromosomes move to the poles in to the poles in anaphase as anaphase as chromosomal spindle chromosomal spindle microtubules shorten microtubules shorten by dissociation of by dissociation of tubulin dimers at the tubulin dimers at the kinetochore. kinetochore.

http://www.dentistry.leeds.ac.uk/biochem/MBWeb/mb2/part1/images/anaphase.gif

Chromosomemovement

Microtubule Motorprotein

Chromosome

Kinetochore

Tubulinsubunits

Telophase and Cytokinesis

Nonkinetochore microtubules elongate the cell

Daughter nuclei form at two poles of cell

Nuclear envelopes arise from fragments of parent cell’s nuclear envelope and other portions of endomembrane system

Chromatin fibers become less tightly coiled

Cytokinesis—division of cytoplasm Formation of cleavage furrow, which

pinches cell in twoFigure 8.8.3

CytokinesisCytokinesis

Typically occurs during telophase.Is the division of the cytoplasm.Is different in plant and animal cells.

CytokinesisCytokinesis

Figure 8.9bFigure 8.9a

Cytokinesis in Plants

No cleavage furrowDuring Telophase, vesicles derived from Golgi

apparatus move along microtubules to middle of cell producing cell plate

Cell plate enlarges until its surrounding membrane fuses with the plasma membrane

The Cell CycleThe Cell Cycle

Review & PracticeReview & Practice

InterphaseInterphase

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

MetaphaseMetaphase

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

ProphaseProphase

AnaphaseInterphase

Metaphase

Interphase

Anaphase

Telophase

Most animal cells divide only when stimulated, and others not at all

In laboratory cultures, most normal cells divide only when Attached to a surface—anchorage dependentHave enough space Have enough growth factor

Factors that affect cell division

Cell Cycle Control SystemCell Cycle Control SystemG1 checkpoint

M checkpointG2 checkpoint

Controlsystem

Cells continue dividing until they touch one another (density-dependent inhibition)

Cells anchor to dish surface and divide.

Figure 8.8A

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 dish with a single layer and then stop (density-dependent inhibition).

Cells are Density DependentCells are Density Dependent

Growth factors are proteins secreted by cells that stimulate other cells to divide

After forming a single layer, cells have stopped dividing.

Figure 8.8B

Providing an additional supply of growth factors stimulates further cell division.

Cells must have Growth FactorsCells must have Growth Factors

Proteins within the cell control the cell cycleSignals affecting critical checkpoints determine

whether the cell will go through a complete cycle and divide

Growth factors signal the cell cycle control system

G1 checkpoint

M checkpoint G2 checkpoint

Controlsystem

For many cells, the G1 checkpoint is the “restriction point” A go-ahead signal indicates that the cell

will complete the cycle and divideIn the absence of a go-ahead signal, the

cell may exit the cell cycle and remain in the non-dividing state called G0 phase

Many human cells are in the G0 phase until they die—muscle and nerve cells

G1 Checkpoint:The binding of growth factors to specific

receptors on the plasma membrane is usually necessary for cell division

Growth factor

Figure 8.8B

Cell cyclecontrolsystem

Plasma membrane

Receptorprotein

Signal transduction pathway

G1 checkpointRelayproteins

G2 Checkpoint:Repair enzymes make sure DNA has been copied correctlyThere are plenty of proteins (growth factors) and organelles present

G2 checkpoint

Controlsystem

Figure 8.9A

M Checkpoint:Anaphase does not begin until all chromosomes are attached to spindle at metaphase plate

Metaphase Anaphase

Cancer cells have abnormal cell cyclesThey divide excessively and can form abnormal masses

called tumors

Cancer cells do not respond normally to the body’s control mechanisms and divide excessively1. Density-independent—make their own growth factors and

continue to divide uncontrolled (“immortal”)

2. Anchorage-independent

Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

Cancer cells: Growing out of Control

Abnormal cells that escape cell-cycle control are products of mutated or transformed normal cells

1. May proliferate to form a tumor—an unregulated growing mass of cells within normal tissue Benign tumor—if cells remain at the original site Malignant tumor—if mass impairs normal

function of one or more organs of the body Excessive proliferation Cells with unusual number of chromosomes Aberrant metabolism Detaches and migrates through body

(metastasis)

Malignant tumors can invade other tissues Malignant tumors can invade other tissues and may kill the organismand may kill the organism

Figure 8.10

Glandulartissue

A tumor grows from a single cancer cell.

Cancer cells invade neighboring tissue.

Lymphvessels

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

Metastasis

Acknowledgements Essential Biology with Physiology 2nd Edition, by Campbell, Reece,

and Simon, ©2007. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2001. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

MeiosisMeiosis

Introduction to HeredityIntroduction to Heredity

Offspring acquire Offspring acquire genes from parents by genes from parents by inheriting inheriting chromosomeschromosomes

Inheritance is possible Inheritance is possible because:because:

– Sperm and ova Sperm and ova carrying each parent’s carrying each parent’s genes are combined in genes are combined in the nucleus of the the nucleus of the fertilized eggfertilized egg

http://www.fertility-treatment.org/images/egg_and_sperm.jpg

•Chromosome-organizational unit of hereditary material in the nucleus of eukaryotic organisms

•Contain hundreds of thousands of genes, each of which is a specific region of the DNA molecule, or locus

Human Life CycleHuman Life Cycle

Each Each somatic cellsomatic cell (body cell) has 46 (body cell) has 46 chromosomes or 23 matching pairs chromosomes or 23 matching pairs ((diploiddiploid))

Karyotype: male

Autosomes: non-sex chromosomes

Sex chromosomes:determine gender (XX; XY)

Human Life CycleHuman Life CycleGametesGametes (sex cells) have a single set (sex cells) have a single set

of 22 autosomes and a single sex of 22 autosomes and a single sex chromosome, either X or Ychromosome, either X or Y

With 23 chromosomes, they are With 23 chromosomes, they are haploidhaploid

haploid number: n = 23

diploid number: 2n = 46

Haploid sperm + haploid ova zygote (2n)fertilization

2n = 26n = ? 13

2n = 44n = ? 22

http://www.davieblint.com/images/http://grove.cs.jmu.edu/parih/images/

2n = 8n = ? 4

http://www.geneticarchaeology.com/Images/Drosophila_With_Extra_Set_Of_Eyes.jpg/

2n = 24n = ? 12

http://mips.gsf.de/projects/plants/images/tomato.jpg

MeiosisReduces chromosome number

(diploid →haploid) Increases genetic variation among

offspringSingle replication of DNA followed by 2

consecutive cell divisions Meiosis IMeiosis II

Produces 4 genetically different haploid daughter cells

In the first division, meiosis I, homologous In the first division, meiosis I, homologous chromosomes are pairedchromosomes are pairedWhile they are paired, they cross over and While they are paired, they cross over and

exchange genetic informationexchange genetic informationThe homologous pairs are then separated, and The homologous pairs are then separated, and

two daughter cells are producedtwo daughter cells are produced

Interphase IInterphase I

Chromosomes replicate (still as chromatin)

Duplicated chromosomes consist of 2 identical sister chromatids attached by centromere

Centriole pairs replicate

Prophase IProphase I

Chromatin condensesChromatin condenses SynapsisSynapsis occurs occurs

(homologues pair)(homologues pair) Chromosomes seen as Chromosomes seen as

distinct structures; distinct structures; each chromosome has each chromosome has 2 chromatids, so each 2 chromatids, so each synapsis forms a synapsis forms a tetradtetrad

Prophase IProphase I

Sister chromatids Sister chromatids held together by held together by centromeres; non-centromeres; non-sister chromatids sister chromatids held together by held together by chiasmata where chiasmata where crossing-overcrossing-over occurs (exchange of occurs (exchange of DNA)DNA)

Late Prophase ILate Prophase I

Centriole pairs move Centriole pairs move apart and spindle fibers apart and spindle fibers formformNuclear envelope Nuclear envelope disappears and nucleoli disappears and nucleoli dispersedisperse

Prophase I

Metaphase IMetaphase I

Homologous Homologous chromosome pairs line chromosome pairs line up along metaphase up along metaphase plateplate

Metaphase Iwww.library.wisc.edu/.../Metaphase_I.html

Anaphase IAnaphase I

Homologous Homologous chromosomes chromosomes separate, separate, independently from independently from othersothers

Anaphase Iin a lily

www.sinauer.com/cooper/4e/micrographs1603.html

Telophase I and CytokinesisTelophase I and Cytokinesis

Each pole now has a Each pole now has a haploid set of haploid set of chromosomes (each with chromosomes (each with 2 sister chromatids)2 sister chromatids)

Usually, cytokinesis Usually, cytokinesis occurs simultaneously occurs simultaneously with telophase I, forming with telophase I, forming 2 haploid daughter cells 2 haploid daughter cells (cleavage furrow forms in (cleavage furrow forms in animals; cell plate forms animals; cell plate forms in plants)in plants)

Telophase I

Meiosis II is essentially the same as mitosisMeiosis II is essentially the same as mitosisThe sister chromatids of each chromosome The sister chromatids of each chromosome

separateseparateThe result is four haploid daughter cellsThe result is four haploid daughter cells

Prophase IIProphase II

Spindle apparatus Spindle apparatus forms and forms and chromosomes move chromosomes move toward metaphase II toward metaphase II plateplate

Prophase II

Metaphase IIMetaphase II

Chromosomes align Chromosomes align singly on the singly on the metaphase platemetaphase plate

Metaphase II

Anaphase IIAnaphase II

Sister chromatids of Sister chromatids of each pair (now individual each pair (now individual chromosomes) separate chromosomes) separate and move toward and move toward opposite poles of the cellopposite poles of the cell

Anaphase II

Telophase II and CytokinesisTelophase II and Cytokinesis

Nuclei form at Nuclei form at opposite poles of the opposite poles of the cellcell

Cytokinesis occurs Cytokinesis occurs producing 4 haploid producing 4 haploid daughter cells (each daughter cells (each genetically different)genetically different)

Telophase II

Key Differences Between Key Differences Between Mitosis and MeiosisMitosis and Meiosis

Meiosis is a reduction divisionMitotic cells produce clones (same xsome #)Meiosis produces haploid cells

Meiosis creates genetic variationMitosis produces 2 identical daughter cells Meiosis produces 4 genetically different

daughter cells Meiosis is 2 successive nuclear divisions

Mitosis has one division

Spermatogenesis Spermatogenesis

Process of sperm production

Results in 4 viable sperm

Oogenesis Oogenesis

Process of egg (ova) production

Results in 1 viable egg and 3 polar bodies that will not survive

Polar bodies result from an uneven division of cytoplasm

Mechanisms of Genetic Mechanisms of Genetic VariationVariation

Crossing-over—exchange of genetic material between non-sister chromatids Results in genetic recombination

Independent assortment—each pair of homologous chromosomes separate independently Results in gametes with different gene combinations

Random fertilization—random joining of two gametes

Crossing over –exchange of corresponding segments between two homologous chromosomes

Genetic recombination results from crossing over during prophase I of meiosis

Crossing over further Crossing over further increases genetic variabilityincreases genetic variability

TetradChaisma

CentromereFigure 8.18A

How crossing over How crossing over leads to genetic leads to genetic recombinationrecombination

Figure 8.18B

Tetrad(homologous pair ofchromosomes in synapsis)

Breakage of homologous chromatids

Joining of homologous chromatids

Chiasma

Separation of homologouschromosomes at anaphase I

Separation of chromatids atanaphase II and completion of meiosis

Parental type of chromosome

Recombinant chromosome

Parental type of chromosome

Gametes of four genetic types

Coat-colorgenes

Eye-colorgenes

Figure 8.17A, B

Coat-color genes Eye-color genes

Brown Black

White Pink

Tetrad in parent cell(homologous pair of

duplicated chromosomes)

Chromosomes ofthe four gametes

Independent AssortmentIndependent Assortment

Figure 8.16

POSSIBILITY 1 POSSIBILITY 2

Two equally probable

arrangements of chromosomes at

metaphase I

Metaphase II

Gametes

Combination 1 Combination 2 Combination 3 Combination 4

Random FertilizationRandom Fertilization

Random as to which gametes join and Random as to which gametes join and form a zygoteform a zygote

Importance of Genetic VariationImportance of Genetic Variation

Essential to evolution (change over time)Essential to evolution (change over time)Variation can cause changes that leads to Variation can cause changes that leads to

different traitsdifferent traitsSome favorableSome favorableSome unfavorableSome unfavorable

StopStop

Errors and Exceptions in Errors and Exceptions in Chromosomal InheritanceChromosomal Inheritance

Alterations in chromosome number or Alterations in chromosome number or structure causes some genetic structure causes some genetic disordersdisordersPhysical and chemical disturbancesPhysical and chemical disturbancesErrors during meiosisErrors during meiosis

To study human chromosomes To study human chromosomes microscopically, researchers stain and microscopically, researchers stain and display them as a karyotypedisplay them as a karyotypeA karyotype usually shows 22 pairs of A karyotype usually shows 22 pairs of

autosomes and one pair of sex chromosomesautosomes and one pair of sex chromosomes

ALTERATIONS OF CHROMOSOME ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURENUMBER AND STRUCTURE

Preparation of a karyotypePreparation of a karyotype

Figure 8.19

Blood culture

Centrifuge

Packed redAnd white blood cells

Hypotonic solution

Fixative

WhiteBloodcells

Centromere

Sisterchromatids

Pair of homologouschromosomes

Human female bandsHuman female bands

Figure 8.19x1

Human female karyotypeHuman female karyotype

Figure 8.19x2

Human male bandsHuman male bands

Figure 8.19x3

Human male karyotypeHuman male karyotype

Figure 8.19x4

Alterations of Chromosome Alterations of Chromosome NumbersNumbers

NondisjunctionNondisjunction—pair of homologues do —pair of homologues do not move apart during Meiosis I, or sister not move apart during Meiosis I, or sister chromatids do not separate during Meiosis chromatids do not separate during Meiosis IIIIResults in uneven distribution of Results in uneven distribution of

chromosomes to daughter cellschromosomes to daughter cells

Alterations of Chromosome Alterations of Chromosome NumbersNumbers

AneuploidyAneuploidy: abnormal chromosome : abnormal chromosome numbernumberTrisomy: three copies of chromosomesTrisomy: three copies of chromosomesMonosomy: one copy of a chromosomeMonosomy: one copy of a chromosomeTrisomy and monosomy are usually lethalTrisomy and monosomy are usually lethal

NondisjunctionNondisjunction

Fertilization after nondisjunction in the Fertilization after nondisjunction in the mother results in a zygote with an mother results in a zygote with an extra chromosomeextra chromosome

Figure 8.21C

Eggcell

Spermcell

n (normal)

Zygote2n + 1

Trisomy 21 (Down Syndrome)*Short stature, characteristic facial features, and heart defects (varying severity)*Most common serious birth defect (1 out of 700 births)*Mothers 35+ years of age have higher chance of having a Down baby

The chance of having a Down syndrome The chance of having a Down syndrome child goes up with maternal agechild goes up with maternal age

Figure 8.20C

Down syndrome karyotypeDown syndrome karyotype

Figure 8.20Ax

Nondisjunction with Sex Chromosomes

Table 8.22

Klinefelter SyndromeKlinefelter Syndrome

Figure 8.22Ax

Male sex organs Male sex organs present, but abnormally present, but abnormally smallsmall

SterileSterile Enlarged breasts and Enlarged breasts and

other feminine contoursother feminine contours Normal intelligenceNormal intelligence The more X-xsomes, the The more X-xsomes, the

more developmental more developmental disabilitiesdisabilities

XYYXYY

Figure 8.22x

Normal malesNormal males Normal testosterone Normal testosterone

levelslevels No increase in No increase in

aggressionaggression

Tend to be taller than Tend to be taller than averageaverage

May have higher risk May have higher risk of learning difficultiesof learning difficulties

Turner SyndromeTurner Syndrome

Lacking a second sex Lacking a second sex chromosomechromosome

Characteristic Characteristic appearanceappearance Short statureShort stature Web of skin b/w neck Web of skin b/w neck

and shoulderand shoulder Sterile—sex organs Sterile—sex organs

do not maturedo not mature Normal intelligenceNormal intelligence

AcknowledgementsAcknowledgements Unless otherwise noted, illustrations are credited to Pearson Unless otherwise noted, illustrations are credited to Pearson

Education which have been borrowed from Education which have been borrowed from BIOLOGY: CONCEPTS BIOLOGY: CONCEPTS AND CONNECTIONSAND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written be reproduced in any format for any purpose without express written permission from the publisher.permission from the publisher.

BIOLOGY: CONCEPTS AND CONNECTIONSBIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2001. These images have Campbell, Reece, Mitchell, and Taylor, ©2001. These images have been produced from the originals by permission of the publisher. been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.purpose without express written permission from the publisher.

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