cell division 100
TRANSCRIPT
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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:
Occurs in somatic(body)cells
Growth, development,replacement & repair
Produces 2 daughter cells
Clones of parent and eachother
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)
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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MEIOSIS & GENETIC VARIATION
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
MEIOSIS & GENETIC VARIATION
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MEIOSIS & GENETIC VARIATION
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)!
MEIOSIS & GENETIC VARIATION
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MEIOSIS & GENETIC VARIATION
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:
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)
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