05. cell division
TRANSCRIPT
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CellDivision
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Cell Division
All cells are derived from pre-existing cells
New cells are produced for
growth and to replace damaged orold cells
Differs in prokaryotes (bacteria)
and eukaryotes (protists, fungi,plants, & animals)
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Types of Cells
Somatic Cells• All body cells except sex cells• Contain diploid (2n) number of chromosomes•
Undergo mitosis
Sex Cells• The gametes, the sperm cell of the male
and the egg cell of the female• Contain haploid number (n) of chromosomes• Undergo mitosis and meiosis
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Keeping Cells Identical
The instructions formaking cell parts
are encoded in theDNA, so each newcell must get a
complete set of theDNA molecules
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DNA ReplicationDNA must be
copied or replicatedbefore celldivision
Each new cell
will then have an identical copy ofthe DNA
Original DNAstrand
Two new,
identical DNA
strands
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Identical Daughter Cells
Parent Cell
Two identical
daughter
cells
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Chromosomes
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Prokaryotic Chromosome
The DNA ofprokaryotes(bacteria) is one,
circularchromosome attached to the
inside of the cellmembrane
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Eukaryotic ChromosomesAll eukaryotic cells store genetic
information in chromosomes Most eukaryotes have between 10 and50 chromosomes in their body cells
Human body cells have 46 chromosomesor 23 identical pairs
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Eukaryotic ChromosomesEach chromosome is composed of a
single, tightly coiled DNA moleculeChromosomes can’t be seen whencells aren’t dividing and are calledchromatin
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Compacting DNA intoChromosomes
DNA istightly
coiledaround proteins
calledhistones
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AP Biology
double-strandedmitotic human
chromosomes
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Chromosomes in Dividing Cells
Duplicatedchromosomes arecalled sister
chromatids &are heldtogether by thecentromere
Called Sister Chromatids
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Mitotic Chromosome
Duplicated chromosome 2 sister chromatids
narrow at centromeres
contain identical
copies of original DNAhomologous
chromosomes homologous
chromosomes
sister chromatids homologous = “same information”
single-strandeddouble-stranded
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KaryotypeA picture of thechromosomes froma human cellarranged in pairs by
sizeFirst 22 pairs arecalled autosomes
Last pair are thesex chromosomes
XX female or XY male
B Gi l?
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Boy or Girl?
Y - Chromosome
X - Chromosome
The Y Chromosome Decides
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Cell Reproduction
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Types of Cell ReproductionAsexual reproduction involves a
single cell dividing to make 2 new,identical daughter cells
Mitosis & binary fission are
examples of asexual reproductionSexual reproduction involves twocells (egg & sperm) joining to make a
new cell (zygote) that is NOT identical to the original cellsMeiosis is an example
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Cell Division inProkaryotes
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Cell Division in Prokaryotes Prokaryotes such as
bacteria divide into 2identical cells by theprocess of binaryfission
Single chromosomemakes a copy ofitself
Cell wall formsbetween thechromosomes dividingthe cell
Parentcell
2 identical daughter cells
Chromosomedoubles
Cell splits
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Prokaryotic CellUndergoing Binary Fission
f B F
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Animation of Binary Fission
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The CellCycle
C ll C l
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Cell Cycle
•The cyclical process ofgrowth and mitosis
Fi Ph f h C ll C l
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Five Phases of the Cell Cycle
G1 - primary growth phaseS – synthesis; DNA replicatedG2 - secondary growth phase
collectively these 3 stages are called interphase
M - mitosisC - cytokinesis
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AP Biology
Cell Cycle
M
Mitosis
G1
Gap 1
G0
Resting
G2
Gap 2
S
Synthesis
Cell has a “life cycle”
cell is formed from
a mitotic division
cell grows & matures
to divide again
cell grows & matures
to never divide again
G1, S, G2, M G1G0
epithelial cells,
blood cells,
stem cells
liver cells
brain / nerve cells
muscle cells
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Interphase
90% of cell life cycle cell doing its “everyday job”
produce RNA, synthesize proteins/enzymes
prepares for duplication if triggered
I’m working here!
Time to divide& multiply!
C ll C l
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Cell Cycle
I t h
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Interphase
Preparatory stage for mitosisCell is not resting
The nucleus is clearly visiblewith one or more distinct nucleoli
Chromosomes appear as
irregular-granular form, thuscannot be recognized
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Interphase
Divided into 3 phases: G1 = 1st Gap (Growth)
cell doing its “everyday job”
cell grows
S = DNA Synthesis copies chromosomes
G2 = 2nd Gap (Growth)
prepares for division
cell grows (more) produces organelles,
proteins, membranes
G0
green = key features
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Interphase
Nucleus well-definedDNA loosely packed in
long chromatin fibers
Prepares for mitosis replicates
chromosome
DNA & proteins
produces proteins &organelles
green = key features
I t h G St
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Interphase - G1 Stage
Pre-Synthesis Interphase
1st growth stage after cell
divisionCells mature by making morecytoplasm & organelles
Cell carries on its normalmetabolic activities
I t h S St
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Interphase – S StageSynthesis stage
DNA is copied or replicated
Twoidenticalcopiesof DNA
Original
DNA
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Synthesis phase of Interphase dividing cell replicates DNA
must separate DNA copies
correctly to 2 daughter cells human cell duplicates ~3 meters DNA
each daughter cell gets complete
identical copy
error rate = ~1 per 100 million bases 3 billion base pairs in mammalian
genome
~30 errors per cell cycle
mutations (to somatic (body) cells)
S phase: Copying / Replicating DNA
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Organizing DNA
DNA is organized inchromosomes double helix DNA molecule
wrapped around histone
proteins like thread on spools
DNA-protein complex =chromatin
organized into long thin fiber condensed further during
mitosis
DNA
histones
chromatin
duplicated mitotic chromosome
ACTGGTCAGGCAATGTC
double stranded chromosome
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Copying DNA & packaging it…
After DNA duplication, chromatin condenses coiling & folding to make a smaller package
DNA
chromatin
mitotic chromosome
Int ph G St
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Interphase – G2 Stage
2nd
Growth StageOccurs after DNA has been copied
All cell structures needed for
division are made (e.g. centrioles)Both organelles & proteins are
synthesized
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double-strandedmitotic human
chromosomes
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Mitotic Chromosome
Duplicated chromosome 2 sister chromatids
narrow at centromeres
contain identical
copies of original DNAhomologous
chromosomes homologous
chromosomes
sister chromatids homologous = “same information” single-stranded double-stranded
Wh t’ H pp nin in Int ph
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What s Happening in Interphase
What the cell looks like
Animal Cell
What’s occurring
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Mitosis
Mitosis
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MitosisDivision of the
nucleusAlso calledkaryokinesis
Only occurs ineukaryotes
Has four stages
Doesn’t occur insome cells suchas brain cells
Four Mitotic Stages
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Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase
green = key features
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Prophase
Chromatin condenses visible chromosomes
chromatids
Centrioles move to oppositepoles of cell
animal cell
Protein fibers cross cell to formmitotic spindle
microtubules
actin, myosin coordinates movement of
chromosomes
Nucleolus disappears
Nuclear membrane breaks down
g y
Early Prophase
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Early ProphaseChromatin in nucleus condenses to
form visible chromosomesMitotic spindle forms from fibers incytoskeleton or centrioles (animal)
Chromosomes
Nucleolus Cytoplasm
Nuclear Membrane
Late Prophase
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Late ProphaseNuclear membrane & nucleolus are
broken downChromosomes continue condensing &are clearly visible
Spindle fibers called kinetochores attach to the centromere of each
chromosomeSpindle finishes forming between thepoles of the cell
Late Prophase
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Late Prophase
Nucleus & Nucleolus have disintegrated
Chromosomes
Spindle Fiber attached to
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Spindle Fiber attached toChromosome
Kinetochore Fiber
Chromosome
Review of Prophase
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Review of Prophase
What the cell looks like
What’s happening
Spindle Fibers
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Spindle FibersThe mitotic spindle form from the
microtubules in plants and centriolesin animal cellsPolar fibers extend from one pole of
the cell to the opposite poleKinetochore fibers extend from thepole to the centromere of the
chromosome to which they attachAsters are short fibers radiatingfrom centrioles
Sketch The Spindle
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Sketch The Spindle
Metaphase
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MetaphaseChromosomes, attached to the
kinetochore fibers, move to the centerof the cell
Chromosomes are now lined up at the
equator
Pole of
the Cell
Equator of Cell
Metaphase
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Metaphase
Chromosomeslined at theEquator
Asters atthe poles
SpindleFibers
Metaphase
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Metaphase
Aster
Chromosomes at Equator
Review of Metaphase
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Review of Metaphase
What the cell looks like
What’s
occurring
Anaphase
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Anaphase
Occurs rapidly
Sisterchromatids are
pulled apart toopposite poles of the cell by
kinetochorefibers
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Separation of chromatids
In anaphase, proteins holding together sister chromatids are inactivated
separate to become individual chromosomes
2 chromosomes1 chromosome
2 chromatids
single-strandeddouble-stranded
Anaphase
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Anaphase
Sister
Chromatidsbeingseparated
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Kinetochores usemotor proteins that
“walk” chromosome
along attached
microtubule
microtubule
shortens by
dismantling atkinetochore
(chromosome) end
Chromosome movement
Anaphase Review
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Anaphase Review
What thecell looks
like
What’soccurring
green = key features
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AP Biology
Telophase
Chromosomes arrive atopposite poles
daughter nuclei form
nuclear envelope formsaround each set of sister chromatids
nucleoli form
chromosomes disperse no longer visible under
light microscope
Spindle fibers disperse
Comparison of Anaphase & Telophase
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Comparison of Anaphase & Telophase
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AP Biology
Mitosis in animal cells
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AP Biology
Mitosis in plant cell
Cytokinesis
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CytokinesisMeans division of the cytoplasm
Division of cell into two,identical halves called daughtercellsIn plant cells, cell plate formsat the equator to divide cell
In animal cells, cleavage furrowforms to split cell
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AP Biology
Cytokinesis in Animals
(play Cells Alive movies here)
(play Thinkwell movies here)
Cytokinesis
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Cytokinesis
Cleavage furrowin animal cell Cell plate inanimal cell
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AP Biology
Cytokinesis in Plants
Plants cell plate forms
vesicles line up at
equator
derived from Golgi
vesicles fuse to form
2 cell membranes
new cell wall laid
down betweenmembranes
new cell wall fuses
with existing cell wall
Mitotic Stages
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Mitotic Stages
Daughter Cells of Mitosis
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Daughter Cells of MitosisHave the same number of
chromosomes as each other and asthe parent cell from which theywere formed
Identical to each other, but smallerthan parent cell
Must grow in size to become maturecells (G1 of Interphase)
Identical Daughter Cells
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Identical Daughter Cells
Chromosome number the same, but cellssmaller than parent cell
What isthe 2n
ordiploidnumber?
2
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Review
ofMitosis
Draw & Learn these Stages
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Draw & Learn these Stages
Draw & Learn these Stages
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Draw & Learn these Stages
Name the Mitotic Stages:
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Interphase
Prophase
Metaphase
Anaphase
Telophase
Name the Mitotic Stages
Name this?
Name this?
Eukaryotic Cell Division
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y
Used for growth andrepair
Produce two new cellsidentical to the original
cell Cells are diploid (2n)
Chromosomes duringMetaphase of mitosis
Prophase Metaphase Anaphase TelophaseCytokinesis
Mitosis Animation
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M tos s n mat onName each stage as you see it occur?
Mitosis in Onion Root Tips
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M n n n p
Do you see any stages of mitosis?
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Test Yourself
over Mitosis
Mitosis Quiz
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Q
Mitosis Quiz
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Q
Name the Stages of Mitosis:
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g f Interphase
Early prophase
Mid-ProphaseLateProphase
Metaphase
LateAnaphase
Early Anaphase
EarlyTelophase,
Begincytokinesis
Late telophase,Advancedcytokinesis
Identify the Stages
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y g
Early, Middle, & Late Prophase
Late Prophase Metaphase Anaphase
Late Anaphase Telophase
Telophase &
Cytokinesis
?
? ? ?
? ? ?
Locate the Four Mitotic
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Locate the Four MitoticStages in Plants
Metaphase
Prophase
Anaphase
Telophase
Uncontrolled Mitosis
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If mitosis is notcontrolled, unlimitedcell division occurscausing cancerous
tumorsOncogenes are special
proteins thatincrease the chance
that a normal celldevelops into a tumorcell
Cancer cells
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Meiosis
Formation of Gametes (Eggs & Sperm)
Facts About Meiosis
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Preceded by interphase whichincludes chromosome replication
Two meiotic divisions --- Meiosis
I and Meiosis IICalled Reduction- division
Original cell is diploid (2n)
Four daughter cells produced thatare monoploid (1n)
Facts About Meiosis
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Daughter cells contain half the
number of chromosomes as theoriginal cell
Produces gametes (eggs & sperm)
Occurs in the testes in males(Spermatogenesis)
Occurs in the ovaries in females(Oogenesis)
More Meiosis Facts
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Start with 46 double strandedchromosomes (2n)After 1 division - 23 double
stranded chromosomes (n)After 2nd division - 23 singlestranded chromosomes (n)
Occurs in our germ cells thatproduce gametes
Why Do we Need Meiosis?
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y
It is the fundamental basis of
sexual reproductionTwo haploid (1n) gametes arebrought together through
fertilization to form a diploid(2n) zygote
Fertilization – “Putting itll h ”
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gall together”
1n =3
2n = 6
Replication of Chromosomes
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pReplication is the
process ofduplicating achromosome
Occurs prior todivision
Replicated copiesare called sister
chromatidsHeld together atcentromere
Occurs inInterphase
A Replicated Chromosome
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p
Homologs
(same genes,different alleles)
Sister
Chromatids (same genes,same alleles)
Gene X
Homologs separate in meiosis I andtherefore different alleles separate.
Meiosis Forms Haploid Gametes
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F m p mMeiosis must reduce the chromosome number
by halfFertilization then restores the 2n number
from mom from dad child
meiosis reduces
genetic content
too
much!
The right
number!
Meiosis: Two Part Cell
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Division
Homologsseparate
Sisterchromatidsseparate
Diploid
MeiosisI
MeiosisII
Diploid
Haploid
Meiosis I: Reduction Division
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Nucleus Spindlefibers Nuclear
envelopeEarly
Prophase I(Chromosomenumberdoubled)
LateProphaseI
MetaphaseI Anaphase
ITelophase I
(diploid)
Prophase I
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p
Early prophase
Homologs pair.Crossing overoccurs.
Late prophase
Chromosomes condense.Spindle forms.Nuclear envelopefragments.
Tetrads Form in Prophase I
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p
Homologous chromosomes
(each with sister
chromatids)
Join to form a TETRAD
Called Synapsis
Crossing-Over
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gHomologous
chromosomes ina tetrad crossover each other
Pieces of
chromosomes orgenes areexchanged
Produces
Geneticrecombination inthe offspring
Homologous Chromosomes
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gDuring Crossing-Over
Crossing-Over
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Crossing-over multiplies the already hugenumber of different gamete types
produced by independent assortment
Metaphase I
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Homologous pairs of chromosomesalign along theequator of the
cell
Anaphase I
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Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their centromeres.
Telophase I
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Nuclear envelopesreassemble.
Spindle disappears.
Cytokinesis divides cellinto two.
Meiosis II
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Only one homolog of each
chromosome is present inthe cell.
Meiosis II produces gametes withone copy of each chromosome andthus one copy of each gene.
Sister chromatids carry
identical geneticinformation.
Gene X
Meiosis II: Reducing
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Chromosome Number
ProphaseII MetaphaseII
AnaphaseII
TelophaseII 4 Identical
haploid cells
Prophase II
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Nuclear envelopefragments.
Spindle forms.
Metaphase II
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Chromosomes align
along equator of cell.
Anaphase II
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Sister chromatids separate andmove to oppositepoles.
Equator
Pole
Telophase II
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Nuclear envelopeassembles.
Chromosomesdecondense.
Spindle disappears.
Cytokinesis dividescell into two.
Results of Meiosis
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Gametes (egg & sperm)form
Four haploid cells withone copy of each
chromosome
One allele of each gene
Different combinationsof alleles for differentgenes along thechromosome
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Gametogenesis
Oogenesisor
Spermatogenesis
Spermatogenesis
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Occurs in the
testesTwo divisionsproduce 4
spermatidsSpermatids matureinto sperm
Men produce about250,000,000sperm per day
Spermatogenesis in theT t
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TestesSpermatid
Spermatogenesis
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Oogenesis
O h
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Occurs in the ovaries
Two divisions produce 3 polar bodies that die and 1 egg
Polar bodies die because of unequaldivision of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocytematures into an ovum (egg) every 28days
Oogenesis in the Ovaries
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Oogenesis
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Oogonium(diploid)
Mitosis
Primaryoocyte(diploid)
Meiosis I
Secondaryoocyte(haploid)
Meiosis II(if fertilizationoccurs)
First polar bodymay divide
(haploid) Polarbodiesdie
Ovum (egg)
Secondpolar body(haploid)
a
A
X
X
a
X
A X
a
X
a
X
Mature
egg
A
X
A
X
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Comparing
Mitosis andMeiosis
Mit sis M i sis
Comparison of Divisions
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Mitosis Meiosis
Number ofdivisions
1 2
Number ofdaughter cells
2 4
Geneticallyidentical?
Yes No
Chromosome # Same as parent Half of parent
Where Somatic cells Germ cells
When Throughout life At sexual maturity