Copyright © 2005 Pearson Prentice Hall, Inc. Cellular Reproduction Cell division in eukaryotes...

Copyright © 2005 Pearson Prentice Hall, Inc.

Cellular Reproduction

• Celldivision in eukaryotesenablesasexual

reproduction (F11.1 p. 186)


The parent cell divides into two daughter cells.

The plasma membrane grows inward at the middle of the cell.

New plasma membrane is added between the attachment points, pushing them further apart.

celldivision

cell growth andDNA replication

The DNA replicates and the two DNA double helices attach to the plasma membrane at nearby points.

The circular DNA double helix is attached to the plasma membrane at one point.

attachmentsite

circularDNA

cellwall

plasmamembrane


ProkaryoticProkaryotic Cell Cycle:Growth & Binary Fission

(F11.2 p187)


G2: cell growth

G1: cell growth and differentiation

prophase

metaphase

anaphase

telo

phase

and

cyto

kinesis

mitotic cell

division

interphase

S: synthesis of DNA; chromosomes are duplicated

G0: non- dividing

Eukaryotic Cell Cycle:

•Interphase•Cell Division

(F11.3 p. 188)


Interphase:Cell Grows in Size Replicates Its DNA


DNA in Eukaryotic Cells Is Organized into Chromosomes

• Eukaryotic Chromosome = 1 Linear DNA Double Helix Bound to Proteins– Chromosome structure (F11.5

p. 190) – Human chromosomes during mitosis (F11.6

p. 191)

– (Duplicated) REPLICATED chromosome (F2 p. 191)

– Daughter chromosomes (F3 p. 191)


nucleosome: DNA wrapped aroundhistone proteins(10 nm diameter)

chromosome:coils gathered ontoprotein scaffold(200 nm diameter)

histone proteins

DNA (2 nm diameter)

DNA coils

coiled nucleosomes(30 nm diameter)

proteinscaffold


sister chromatids centromere


genes

centromere

telomeres


independentdaughterchromosomes,each with oneidentical DNAdouble helix

sisterchromatids

duplicatedchromosome(2 DNA double helices)


DNA in Eukaryotic Cells Is Organized into Chromosomes

• Eukaryotic Chromosomes: – Usually Occur in Homologous Pairs

•1 from Mom & 1 from Dad

– Homologs Have Similar (NOT IDENTICAL) Genetic Information•Some from Mom & Some from Dad

– Karyotype of a human male (F11.7 p. 191)


Cellular Reproduction• Two Types of Eukaryotic Cell

Division : – Mitotic Cell Division – Meiotic Cell Division

•Figure 11.4 (Hide/Reveal) Mitotic and meiotic cell division in the human life cycle (p. 189)

•Unnumbered Figure 1 Chromosome (p. 190)


Mitotic Cell Division

• Mitotic cell division in an animal cell (F11.8 p.

192)


INTERPHASE MITOSIS

LATE INTERPHASE

nuclearenvelope chromatin

nucleolus

centriolepairs

LATE PROPHASE METAPHASE

beginning ofspindle formation

kinetochore

pole

polecondensingchromosomes

spindlemicrotubules

Duplicated chromosomes inrelaxed state; duplicated centrioles remain clustered.

Chromosomes condense and shorten; spindle microtubules begin to form between separating centriole pairs.

Nucleolus disappears; nuclear envelope breaks down; spindle microtubules attach to the kinetochore of each sister chromatid.

Kinetochores interact; spindle microtubules line up chromosomes at cell's equator.

EARLY PROPHASE


INTERPHASE

ANAPHASE

"free" spindlefibers

chromosomesextending nuclear envelope

re-forming

Sister chromatids separate and move to opposite poles of the cell; spindle microtubules push poles apart.

One set of chromosomes reaches each pole and relaxes into extended state; nuclear envelopes start to form around each set; spindle microtubules begin to disappear.

Cell divides in two; each daughter cell receives one nucleus and about half of the cytoplasm.

Spindles disappear, intact nuclear envelopes form, chromosomes extend completely, and the nucleolus reappears.

TELOPHASE INTERPHASE OFDAUGHTER CELLS

CYTOKINESIS


electric pulsefused cells

The egg cell without a nucleus and the quiescent udder cell are placed side by side in a culture dish. An electric pulse stimulates the cells to fuse and initiates mitotic cell division.

nucleus isremovedegg

cell

DNA

donor cellfrom udder

Finn Dorset ewe

Cells from the udder of a Finn Dorset ewe are grown in culture with low nutrient levels. The starved cells stop dividing and enter the non-dividing G0 phase of the cell cycle.Blackface ewe

Meanwhile, the nucleus is sucked out of an unfertilized egg cell taken from a Scottish Blackface ewe. This egg will provide cytoplasm and organelles but no chromosomes.


The cell divides, forming an embryo that consists of a hollow ball of cells.

The Blackface ewe gives birth to Dolly, a female Finn Dorset lamb, a genetic twin of the Finn Dorset ewe.

The ball of cells is implanted into the uterus of another Blackface ewe.


Mitotic Cell Division• Prophase

– Chromosomes Condense, Spindle Microtubules Form & Attach to the Chromosomes

• Metaphase– Chromosomes Align Along the Equator of the Cell

• Anaphase– Sister Chromatids Separate & Pulled to Opposite Poles

of the Cell• Telophase

– Nuclear Envelopes Form Around Both Groups of Chromosomes

• Cytokinesis– Cytoplasm Is Divided Between Two Daughter Cells– Cytokinesis in an animal cell (F11.9 p.

197)

– Cytokinesis in a plant cell (F11.10 p. 197)


The waist completelypinches off, formingtwo daughter cells.

The microfilament ringcontracts, pinchingin the cell's “waist.”

Microfilaments form a ring around the cell's equator.


Complete separation of daughter cells.

Vesicles fuse to form a new cell wall (red) and plasma membrane (yellow) between daughter cells.

cell wall

Golgi complex

plasma membranecarbohydrate-filled vesicles

Carbohydrate-filled vesicles bud off the Golgi complex and move to the equator of the cell.


Cellular Reproduction• Two Types of Eukaryotic Cell Division :

– Mitotic Cell Division – Meiotic Cell Division

•Mitotic & meiotic cell division in human life cycle

(F11.4 p. 189)


embryo

mitosis,differentiation,and growth

meiosis in testes

meiosis inovaries

egg

sperm

adultsmitosis,differentiation, and growth

fertilization

fertilizedegg

mitosis,differentiation,and growth

baby


gene 1 gene 2

same alleles different alleles


sisterchromatids

homologouschromosomes



Meiotic Cell Division Produces Haploid Cells

• Meiosis Separates Homologous Chromosomes, Producing Haploid Daughter Nuclei

• Meiotic Cell Division Followed by Fusion of Gametes Keeps the Chromosome Number Constant from Generation to Generation

• Meiosis I Separates Homologous Chromosomes into Two Haploid Daughter Nuclei– During Prophase I, Homologous Chromosomes Pair Up and

Exchange DNA• Homologous chromosomes (F5 p. 198)• Two daughter nuclei (F6 p. 198)• Four haploid cells (F 7 p. 199)• Meiotic cell division (F8 p. 199)• Meiotic cell division in an animal cell (F11.11 p.

200)


meioticcell division

fertilization

2n

2n

2n n

n


MEIOSIS I

recombinedchromosomes

spindlemicrotubule

paired homologouschromosomes

chiasma


MEIOSIS I

Prophase I. Duplicatedchromosomes condense.Homologous chromosomespair up and chiasmata occuras chromatids of homologuesexchange parts. The nuclearenvelope disintegrates, andspindle microtubules form.

Metaphase I. Pairedhomologous chromosomesline up along the equator ofthe cell. One homologue ofeach pair faces each poleof the cell and attaches tospindle microtubules via itskinetochore (blue).

Anaphase I. Homologuesseparate, one member ofeach pair going to each poleof the cell. Sister chromatidsdo not separate.

Telophase I. Spindlemicrotubules disappear. Twoclusters of chromosomes haveformed, each containing onemember of each pair ofhomologues. The daughter nucleiare therefore haploid. Cytokinesiscommonly occurs at this stage.There is little or no interphasebetween meiosis I and meiosis II.

paired homologouschromosomes

recombinedchromosomes

spindlemicrotubule

chiasma


MEIOSIS II

Prophase II.If chromosomeshave relaxed aftertelophase I, theyrecondense. Spindlemicrotubules re-formand attach to thesister chromatids.

Metaphase II.Chromosomes lineup along the equator,with sister chromatidsof each chromosomeattached to spindlemicrotubules that leadto opposite poles.

Anaphase II.Chromatids separateinto independentdaughter chromosomes,one former chromatidmoving toward eachpole.

Telophase II.Chromosomes finishmoving to oppositepoles. Nuclearenvelopes re-form,and the chromosomesbecome extendedagain (not shown here).

Four haploid cells.Cytokinesis results infour haploid cells, each containing one member of each pair of homologouschromosomes (shownhere in condensed state).


Meiotic Cell Division Produces Haploid Cells

• Meiosis I– Metaphase I, Paired Homologs Line Up at the Equator of the Cell– Anaphase I, Homologs Separate– Telophase I, Two Haploid Clusters of Duplicated Chromosomes

Form– Mitosis, Meiosis I (F9, 10

p. 202)

• Meiosis II Separates Sister Chromatids into Four Daughter Nuclei– The mechanism of crossing over

(F11.12p. 200)– Comparison of Animal Cell Mitotic & Meiotic Cell Divisions (T11.1

p. 203)

– Chromosome configurations at metaphase I F11


Recombination enzymes bind to the joined chromosomes.

recombinationenzymes

Recombination enzymes and protein zippers leave. Chiasmata remain, helping to hold homologous chromosomes together.

chiasmaRecombination enzymes snip chromatids apart and reattach the free ends. Chiasmata (the sites of crossing over) form when one end of the paternal chromatid (yellow) attaches to the other end of a maternal chromatid (purple).

chiasmaDuplicated homologous

chromosomes pair up side by side.

sisterchromatids ofone duplicatedhomologue

pair of homologous,duplicated chromosomes

Protein strands “zip” the homologous chromosomes together.

protein strandsjoining duplicatedchromosomes

direction of“zipper”formation


spindlemicrotubules

duplicatedchromosomes


Why Do So Many Organisms Reproduce

Sexually?

• Mutations in DNA Are the Ultimate Source of Genetic Variability

• Sexual Reproduction May Combine Different Parental Alleles in a Single Offspring


How Do Meiosis & Sexual Reproduction Produce Genetic

Variability?• Shuffling of Homologues Creates Novel

Combinations of Chromosomes• Crossing Over Creates Chromosomes

with Novel Combinations of Genes• Fusion of Gametes Adds Further

Genetic Variability to the Offspring


spindlemicrotubules

duplicatedchromosomes

Copyright © 2005 Pearson Prentice Hall, Inc. Cellular Reproduction Cell division in eukaryotes...

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