cell division chapter 5. why does a cell divide? -as a cell absorbs nutrients and gets larger, the...
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Why does a cell divide?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
► 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 DecreaseCell Increase and Decrease
Cell Division, Cell DeathCell Division, Cell Death
► Functions of Cell DivisionFunctions of Cell Division MitosisMitosis
► Increase number of somatic cellsIncrease number of somatic cells► Wound healingWound healing► Asexual reproductionAsexual reproduction
MeiosisMeiosis► Production of gametes (germ cells, sperm and eggs)Production of gametes (germ cells, sperm and eggs)
Apoptosis—Programmed cell deathApoptosis—Programmed cell death
Amoeba
Interphase—3 StagesInterphase—3 Stages►GG11 stage stage – –
cell growthcell growth cell doubles its organellescell doubles its organelles accumulates materials for DNA synthesisaccumulates materials for DNA synthesis
►S stageS stage – – DNA synthesis occursDNA synthesis occurs DNA replication results in duplicated DNA replication results in duplicated
chromosomeschromosomes
►GG22 stage stage – – cell synthesizes proteins needed for cell cell synthesizes proteins needed for cell
divisiondivision
Same sizeSame sizeSame genes in Same genes in the same orderthe same order
Homologous Chromosomes
Chromosome pairs, one from mom, one from dad
a. Diploid number (2n) - total number of chromosomes
in a cell (somatic cells) b. Haploid number (n) - only one homologue of each chromosome is present (gametes)
The Cell CycleThe Cell Cycle
► Interphase Interphase (90% of (90% of
cycle)cycle) • G1 phase~ • G1 phase~ growth growth • S phase~ • S phase~ synthesis of DNA • G2 synthesis of DNA • G2 phase~ preparation for phase~ preparation for
cell divisioncell division
► Mitotic phaseMitotic phase • Mitosis~ nuclear • Mitosis~ nuclear division • Cytokinesis~ division • Cytokinesis~ cytoplasm cytoplasm divisiondivision
The Mitotic StageThe Mitotic Stage
►Following interphase is the Following interphase is the M stageM stage, , including mitosis and cytokinesis.including mitosis and cytokinesis.
►During mitosis, During mitosis, sister sister chromatidschromatids of of each chromosome separate.each chromosome separate.
►The cell cycle ends when The cell cycle ends when cytokinesis, the cleaving of the cytokinesis, the cleaving of the cytoplasm, is complete.cytoplasm, is complete.
Figure 5.30 The DNA double helix and its replicationFigure 5.30 The DNA double helix and its replication
Sister chromatids attached at centromere
Sister chromatids separate during cell division
Duplicated ChromosomeDuplicated Chromosome
► PloidyPloidy - number of copies of each chromosome - also number of genomes
► HaploidHaploid (N) (N)= one set of unpaired chromosomes= one set of unpaired chromosomes► DiploidDiploid (2N or 2n)= one set of paired (2N or 2n)= one set of paired
chromosomeschromosomes► TriploidTriploid = three copies of each chromosome = three copies of each chromosome► TetraploidTetraploid = four copies of each chromosome = four copies of each chromosome► HexaploidHexaploid = six copies of each chromosome = six copies of each chromosome► Etc, etc, etcEtc, etc, etc
PLOIDY
Chloroplasts have their own DNA, separate fromplant nuclear DNA, derived from their cyanobacterial origin
Most eukaryotes also have a mitochondrial genome, derived from a eubacterial endosymbiont ancestor
Human mtDNA 37 genes, 16 kilobasepairs
ApoptosisApoptosis►ApoptosisApoptosis - - programmed cell programmed cell death.death.
►Function?Function?
Mitosis OverviewMitosis Overview
►1 diploid (2N) cell>>>>2 diploid 1 diploid (2N) cell>>>>2 diploid (2N)cells(2N)cells
►Genetically identical daughter cellsGenetically identical daughter cells►Function---Maintain the somatic cell Function---Maintain the somatic cell
chromosome numberchromosome number
Spindle and FibersSpindle and Fibers► Spindle made of?Spindle made of?
microtubules that that disassemble and disassemble and assemble.assemble.
► Centrosomes (MTOC)——function? function?
► Types of Fibers Types of Fibers Polar Spindle Fibers Centomeric (kinetochore)
fibers Asters
Phases of MitosisPhases of Mitosis
►ProphaseProphase►MetaphaseMetaphase►AnaphaseAnaphase►TelophaseTelophase►PPretty retty MMen en AAre re TToughough►OverviewOverview
As cell enters mitosis from interphase it has 2 complete sets of chromosomes because of replication in the S phase. Each set must be re-arranged and distributed into the 2 new daughter nuclei. This is mitosis.
Results of MitosisResults of Mitosis
►Two daughter nuclei Two daughter nuclei
►Each with same Each with same chromosome number chromosome number as parent cellas parent cell
►Genetically identical Genetically identical to each other and to each other and the parent cellthe parent cell
-Animal cells: Cleavage furrow forms from outside in.
-
Plant cells: Division plate forms from inside out.
CYTOKINESIS – Cytoplasm splits into 2 cells.
REVIEW OF MITOSISREVIEW OF MITOSIS
Parent Cell
DNA Synthesis (“S” Phase)
Mitosis & Cytokinesis
Two daughter cells
Remember:Mitosis Is Part Of The Cell Cycle!!
Parent cell and daughter cells contain the same complement of chromosomes.
Cell Division in ProkaryotesCell Division in Prokaryotes
►Binary fission---process of asexual ---process of asexual reproduction in prokaryotes.reproduction in prokaryotes.
►Two daughter cells Two daughter cells ► Identical to the original parent cell and Identical to the original parent cell and
each other each other► All contain a single chromosome.All contain a single chromosome.
Overview of MeiosisOverview of Meiosis
►1 diploid (2N) cell>>>>4 haploid 1 diploid (2N) cell>>>>4 haploid (1N) cells(1N) cells
►Genetically unique daughter cellsGenetically unique daughter cells►Function---reduce the chromosome Function---reduce the chromosome
number by ½number by ½►The main source of genetic The main source of genetic
diversity in sexually reproducing diversity in sexually reproducing organismsorganisms
MEIOSISMEIOSISTwo Parts:Two Parts:
► Meiosis I:Meiosis I: Separation of Separation of homologous homologous
pairs pairs Ploidy Level?Ploidy Level?
► Meiosis II:Meiosis II: Separation of Separation of sister sister
chromatidschromatids Ploidy Level?Ploidy Level?
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 germ cells (immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells► Distinct from parent and
each other
Daughter cells are haploid (1N)
Genetic RecombinationGenetic Recombination
• Meiosis increases genetic diversity. Two points of genetic recombination.
• Crossing-over of nonsister of nonsister chromatids—Prophase 1chromatids—Prophase 1
• Independent assortment of of homologous chromosomes homologous chromosomes during Metaphase 1during Metaphase 1
More TerminologyMore TerminologyCrossing OverCrossing Over
►Segments of paternal/maternal chromatids Segments of paternal/maternal chromatids exchange during Meiosis Iexchange during Meiosis I
Synapsis Synapsis ►Process of homologs coming together Process of homologs coming together
physically during Meiosis Iphysically during Meiosis I
TetradTetrad ►Consists of 4 sister chromatids from 2 Consists of 4 sister chromatids from 2
homologous chromosomeshomologous chromosomes
Meiosis in DetailMeiosis in Detail
►PhasesPhases ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase telophasetelophase
► Interkinesis.Interkinesis.►Replication of DNA??Replication of DNA??
Sources of Genetic VariationSources of Genetic Variation
► Three sources of genetic Three sources of genetic recombination:recombination:
1)1) Independent alignment – Independent alignment – metaphase Imetaphase I
2)2) Crossing-over---prophase ICrossing-over---prophase I3)3) FertilizationFertilization
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 germ cells
(immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells► Distinct from parent and
each other
Daughter cells are haploid (1N)
comparison
FERTILIZATION RESTORES FERTILIZATION RESTORES FULL SET OF FULL SET OF
CHROMOSOMESCHROMOSOMESFemale gamete Male gamete
fertilization
Diploid zygote contains homologous pairs of chromosomes
Sources of Genetic VariationSources of Genetic Variation
► Three sources of genetic Three sources of genetic recombination:recombination:
1)1) Independent assortment – Independent assortment – metaphase Imetaphase I
2)2) Crossing-over---prophase ICrossing-over---prophase I3)3) FertilizationFertilization
MEIOSIS & GENETIC MEIOSIS & GENETIC VARIATIONVARIATION
Independent Independent AssortmentAssortment
► Diploid organisms Diploid organisms can produce 2can produce 2n n diff. diff. gametesgametes
► Ea. homologous pair can Ea. homologous pair can orient in two different orient in two different waysways
► Humans: 2Humans: 22323 = = 8,388,608 8,388,608
((est. 8.4 millionest. 8.4 million))
Each homologous pair can orient in either of two ways
HYPOTHETICAL EXAMPLE OF INDEPENDENT ASSORTMENT
Gene for
browneyes
Eye color
Gene for
blueeyes
Gene for
black hair
r
Gene for red hair
Hair color
INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT
OR
During meiosis I, tetrads can line up 2n different ways.
Brown eyesBlack hair
Blue eyesRed hair
Brown eyesRed hair
Blue eyesBlack hair
Meiosis I & II
MEIOSIS & GENETIC MEIOSIS & GENETIC VARIATIONVARIATION
Crossing Over:Crossing Over:► Physical exchange of Physical exchange of
sections of chromosomessections of chromosomes► Results in shuffling of Results in shuffling of
genome genome ► New combo of genes on New combo of genes on
chromosomes (chromosomes (recombinationrecombination))
A single crossover in each A single crossover in each homologous pair = 5.0 x 10 homologous pair = 5.0 x 10 27 27
different zygotes possible different zygotes possible (4951,760,200,000,000,000,000,0(4951,760,200,000,000,000,000,000,000)!00,000)!
MEIOSIS & GENETIC MEIOSIS & GENETIC VARIATIONVARIATION
Random Fertilization:Random Fertilization: ► Each human can produce Each human can produce
an nearly 8.4 million an nearly 8.4 million different kinds of gametesdifferent kinds of gametes
► Crossing over not taken into Crossing over not taken into account!!!account!!!
► Sex yields:Sex yields:► 8.4 mill x 8.4 mill = 70.6 x 10 8.4 mill x 8.4 mill = 70.6 x 10 1212
genetically distinct offspring genetically distinct offspring can be producedcan be produced
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 germ cells
(immature reproductive cells)
Production of gametes (sex cells)
Produce 4 daughter cells► Distinct from parent and
each other
Daughter cells are haploid (1N)
comparison