Cell Division 100

8/12/2019 Cell Division 100

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Cell Division

Chapter 5


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Why does a cell divide?

-As a cell absorbs nutrients and gets larger, the

volume of the cell increases faster than the

surface area.

-Therefore, the demands of the cell (the volume)exceed the ability of the cell to bring in nutrients

and export wastes. Solution?

Divide into two smaller cells


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Cell division:

Mitosis(division of nucleus or

karyokinesis) Cytokinesis(division of cytoplasm)

Apoptosis(cell death) decreases the

number of cells. Both cell increase and apoptosis

occur during normal development

and growth.

Cell Increase and Decrease


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Cell Division, Cell Death

Functions of Cell Division

Mitosis

Increase number of somatic cells

Wound healingAsexual reproduction

Meiosis

Production of gametes (germ cells, sperm and eggs)

ApoptosisProgrammed cell death

Amoeba


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Asexual reproduction 2

Hydra


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The cell cycle


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Interphase3 StagesG1stage

cell growth

cell doubles its organelles

accumulates materials for DNA synthesis

S stage DNA synthesis occurs

DNA replication results in duplicated

chromosomesG2stage

cell synthesizes proteins needed for cell

division


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Chromosome

Condensed chromatin

Chromosomes


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Same size

Same genes in thesame order

Homologous Chromosomes

Chromosome pairs, one from mom, one from dad


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a. Diploid number (2n)- total number of chromosomesin a cell (somatic cells)

b. Haploid number (n)- only one homologue of each

chromosome is present (gametes)


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The Big Picture


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The Cell Cycle

Interphase (90% of

cycle) G1 phase~growth S phase~synthesis of DNA G2phase~ preparation for

cell division

Mitotic phase Mitosis~ nucleardivision Cytokinesis~cytoplasm division


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The Mitotic Stage

Following interphase is the M stage,including mitosis and cytokinesis.

During mitosis, sister chromatidsof eachchromosome separate.

The cell cycle ends when cytokinesis, the

cleaving of the cytoplasm, is complete.

Fi 30 Th DNA d bl h li d i li i


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Figure 5.30 The DNA double helix and its replication


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In mitosis

eachchromosome

is replicated

and thendivides


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Sister chromatids

attached at

centromere

Sister chromatids

separate during cell

division

Duplicated Chromosome


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Ploidy- number of copies of eachchromosome - also number of genomes

Haploid(N)= one set of unpaired chromosomes

Diploid(2N or 2n)= one set of paired

chromosomes

Triploid= three copies of each chromosome

Tetraploid= four copies of each chromosome

Hexaploid= six copies of each chromosome

Etc, etc, etc

PLOIDY


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Chloroplasts have their own DNA, separate from

plant nuclear DNA, derived from their cyanobacterial origin


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Most eukaryotes also have a mitochondrial genome,

derived from a eubacterial endosymbiont ancestor

Human mtDNA 37 genes, 16 kilobasepairs


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ApoptosisApoptosis- programmedcell death.

Function?


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Mitosis Overview

1 diploid (2N) cell>>>>2 diploid (2N)cells

Genetically identical daughter cells

Function---Maintain the somatic cellchromosome number


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Mitosis Overview


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Chromosome Distribution


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Spindle and Fibers

Spindle made of?

microtubulesthatdisassemble and assemble.

Centrosomes (MTOC)function?

Types of Fibers

Polar Spindle Fibers

Centomeric (kinetochore)

fibers Asters


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Phases of Mitosis

Prophase

Metaphase

AnaphaseTelophase

Pretty Men Are Tough

Overview
http://www.cellsalive.com/mitosis.htmhttp://www.cellsalive.com/mitosis.htm


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As cell enters mi tosis

from interphase it has

2 complete sets of

chromosomes because

of replication in the Sphase. Each set must

be re-arranged and

distr ibuted into the 2new daughter nuclei.

This is mitosis.


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Late Interphase


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Early Prophase


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Late Prophase


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Metaphase


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Anaphase


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Telophase

Review
http://www.cellsalive.com/mitosis.htmhttp://www.cellsalive.com/mitosis.htm


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Results of Mitosis

Two daughter nuclei

Each with same

chromosome numberas parent cell

Genetically identical toeach other and theparent cell


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-Animal cells: Cleavage furrowforms from

outside in.

-

Plant cells: Division plateforms from inside

out.

CYTOKINESISCytoplasm splits into2 cells.


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Cytokinesis in Animal Cells


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Cytokinesis in plant cells


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REVIEW OF MITOSIS

Parent Cell

DNA Synthesis (S Phase)

Mitosis & Cytokinesis

Two daughter cells

Remember:

Mitosis Is PartOf The Cell Cycle!!

Parent cell and daughter cells contain the same complement of chromosomes.


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Cell Division in Prokaryotes

Binary fission---process of asexualreproduction in prokaryotes.

Two daughter cells

Identical to the original parent cell andeach other

All contain a single chromosome.


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The Big Picture


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Overview of Meiosis

1 diploid (2N) cell>>>>4 haploid(1N) cells

Genetically unique daughter cellsFunction---reduce the chromosome

number by

The main source of genetic diversity insexually reproducing organisms


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MEIOSIS

Two Parts:

Meiosis I:

Separation of homologouspairs

Ploidy Level?

Meiosis II: Separation of sister

chromatids

Ploidy Level?


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COMPARISON-- MITOSIS and MEIOSIS

Mitosis:

Occurs in somatic(body)cells

Growth, development,replacement & repair

Produces 2 daughter cells Clones of parent and each

other

Daughter cells are diploid(2N)

Meiosis:

Occurs in germcells(immature reproductive cells)

Production of gametes(sexcells)

Produce 4 daughter cells Distinct from parent and each

other

Daughter cells are haploid(1N)


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Genetic Recombination

Meiosis increases genetic diversity.Two points of genetic

recombination. Crossing-overof nonsister

chromatidsProphase 1

Independent assortmentofhomologous chromosomes duringMetaphase 1


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Synapsis and crossing-over

Defs


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More TerminologyCrossing Over

Segments of paternal/maternal chromatids exchangeduring Meiosis I

SynapsisProcess of homologs coming together physicallyduring Meiosis I

Tetrad

Consists of 4 sister chromatids from 2 homologouschromosomes


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Independent assortment


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Meiosis in Detail

Phases Prophase

Metaphase

Anaphase telophase

Interkinesis.

Replication of DNA??


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Meiosis I in an animal cell


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Meiosis II


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Sources of Genetic Variation

Three sources of geneticrecombination:

1) Independent alignmentmetaphase I

2) Crossing-over---prophase I

3) Fertilization


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SUMMARY-- MITOSIS and MEIOSIS

Mitosis:



Produces 2 daughter cells

Clones of parent and eachother


Meiosis: Occurs in germcells

(immature reproductive cells)



other


comparison
http://www.lewport.wnyric.org/jwanamaker/animations/mitosis.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/meiosis.htmlhttp://www.pbs.org/wgbh/nova/baby/divi_flash.htmlhttp://www.pbs.org/wgbh/nova/baby/divi_flash.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/meiosis.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/mitosis.html


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Meiosis compared to mitosis


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Life cycle of humans


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Spermatogenesis


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Oogenesis


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FERTILIZATION RESTORESFULL SET OF CHROMOSOMES

Female gamete Male gamete

fertilization

Diploid zygote contains

homologous pairs of

chromosomes


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Sources of Genetic Variation

Three sources of geneticrecombination:

1) Independent assortmentmetaphase I

2) Crossing-over---prophase I

3) Fertilization

MEIOSIS & GENETIC VARIATION


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Independent

Assortment

Diploid organisms can

produce 2n diff.gametes

Ea. homologous pair can

orient in two differentways

Humans: 223= 8,388,608

(est. 8.4 million)

Each homologous pair can

orient in either of two ways

HYPOTHETICAL EXAMPLE OF


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HYPOTHETICAL EXAMPLE OFINDEPENDENT ASSORTMENT

Gene

for

brown

eyes

Eye color

Gene

for

blue

eyes

Gene

for

black

hair

r

Gene

for red

hair

Hair color


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INDEPENDENT ASSORTMENT

OR

During meiosis I, tetrads can line up 2ndifferent ways.

Brown eyes

Black hair

Blue eyes

Red hairBrown eyes

Red hair

Blue eyes

Black hair

Meiosis I & II



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Crossing Over:

Physical exchange of sections ofchromosomes

Results in shuffling of genome New combo of genes on chromosomes

(recombination)

A single crossover in each homologouspair = 5.0 x 10 27 different zygotespossible

(4951,760,200,000,000,000,000,000,000)!



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Random Fertilization:

Each human can produce annearly 8.4 million differentkinds of gametes

Crossing over not taken intoaccount!!!

Sex yields:8.4 mill x 8.4 mill = 70.6 x 10 12

genetically distinct offspring can beproduced


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SUMMARY-- MITOSIS and MEIOSIS

Mitosis:



Produces 2 daughter cells Clones of parent and each

other


Meiosis: Occurs in germcells

(immature reproductive cells)



other

http://www.lewport.wnyric.org/jwanamaker/animations/mitosis.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/meiosis.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/meiosis.htmlhttp://www.lewport.wnyric.org/jwanamaker/animations/mitosis.html

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Cell Division 100