Download Cell Cycle & Cell Division

Cellular
Division
1
Cell Division
All cells are derived from pre-
existing cells
New cells are produced for
growth and to replace damaged or
old cells
Division differs in prokaryotes
(bacteria) and eukaryotes
(protists, fungi, plants, & animals)
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Why Cells Divide
• To replace dead/ dying cells
• Wound repair after you have an injury.
• Growth and Development
– The more you grow, the more cells you need.
3
Keeping Cells Identical
• Cell division results in
two identical cells.
• The instructions for
making cell parts are
encoded in the DNA.
• DNA is in the nucleus.
4
DNA Replication
DNA must be copied
or replicated before
Original DNA
cell division
strand
Each new cell will
then have an
identical copy of
the DNA
Two new,
identical DNA
strands
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Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
(dividing)
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Chromosomes
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Prokaryotic Chromosome
The DNA of
prokaryotes
(bacteria) is one,
circular chromosome
attached to the
inside of the cell
membrane
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Eukaryotic Chromosomes
All eukaryotic cells store genetic
information in chromosomes
Human body cells have 46 chromosomes
or 23 identical pairs
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Eukaryotic Chromosomes
Each chromosome is composed of a
single, tightly coiled DNA molecule
Chromosomes can’t be seen when
cells aren’t dividing and are called
chromatin
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Chromosomes in Dividing Cells
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister Chromatids
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Types of Chromosomes
Sex Chromosomes
– Determine the sex or gender of an organism
– Contain other genes for other
characteristics
– XX=girl, XY=boy
Autosomes
-All other chromosomes
-Homologous Chromosomes
- copies of each autosome (1 from each
parent)
- same size, shape and carry the same
genes for the traits
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Karyotype
A picture of the
chromosomes from
a human cell
arranged in pairs by
size
First 22 pairs are
called autosomes
Last pair are the
sex chromosomes
XX female or XY
male
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Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome
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Haploid vs Diploid Cells
• Diploid (2n)
– Most cells in the body
– Two sets of chromosomes
• Homologous chromosomes and two sex
chromosomes
• Example: Humans have 46 chromosomes
(22 homologous and 2 sex chromosomes
• Haploid (1n)
– Sex cells (sperm and eggs)
– One set of chromosomes (1/2 the number of
chromosomes)
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Cell Reproduction
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Types of Cell Reproduction
Asexual reproduction involves a
single cell dividing to make 2 new,
identical daughter cells
Mitosis & binary fission are
examples of asexual reproduction
Sexual reproduction involves two
cells (egg & sperm) joining to make a
new cell (zygote) that is NOT
identical to the original cells
Meiosis is how egg and sperm are made
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Cell Division in
Prokaryotes
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Cell Division in Prokaryotes
 Prokaryotes such as
bacteria divide into 2 Parent
cell
identical cells by the
process of binary
fission
Chromosome
 Single chromosome
doubles
makes a copy of
itself
 Cell wall forms Cell splits
between the
chromosomes dividing
the cell
2 identical daughter cells
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The Cell
Cycle
Eukaryotic Cells
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3 Phases of the Cell Cycle
Interphase
G1 - primary growth phase
S – synthesis; DNA replicated
G2 - secondary growth phase
collectively these 3 stages are called
interphase
M – mitosis (Pro, Meta, Ana, Telo)
C – cytokinesis (division of cytoplasm)
end of telophase
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Cell Cycle
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Three parts of Interphase
1. G1 Stage
1st growth stage after cell
division
Cells mature by making more
cytoplasm & organelles
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Three parts of Interphase
2. S Stage
Synthesis stage
DNA is copied or replicated
Two
identical
copies
of DNA
Original
DNA
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Three parts of Interphase
3. G2 Stage
2nd Growth Stage
Occurs 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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Sketch the Cell Cycle
DNA Copied
Cells
Mature
Daughter
Cells
Cells prepare for
Division
Cell Divides into
Identical cells
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Mitosis
(4 Phases)
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Mitosis
Division of the
nucleus
Also called
karyokinesis
Eukaryotes only
Has four stages
Doesn’t occur in
some cells such
as brain cells
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Four Mitotic Stages
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
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Prophase
• Chromatin
condenses to
chromosomes.
• Nucleolus and
nuclear membrane
disappears.
• Spindle starts to
form.
• Centrioles at
opposite ends.
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Metaphase
• Chromosomes line
up in the middle
(metaphase plate)
• Chromosomes
attach to spindle at
centromere.
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Anaphase
• Sister chromatids
separate and move
toward opposite
ends of the cell.
• Cell begins to
elongate.
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Telophase
• Reverse prophase
• Nuclear membrane
reforms
• Nucleolus
reappears
• Chromosomes uncoil
to chromatin.
• Cells begin to
divide.
• Spindle disappears.
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Cytokinesis
• Division of the
cytoplasm.
• Results in the
formation of two
IDENTICAL
daughter cells.
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Cytokinesis
• Animal Cellscleavage furrow
forms.
• Plant Cells- cell
plate divides cells
forming a new cell
wall.
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Eukaryotic Cell Division
 Used for growth and
repair
 Produce two new cells
identical to the original
cell
 Cells are diploid (2n)
Prophase
Metaphase
Chromosomes during Metaphase of mitosis
Anaphase Telophase Cytokinesis
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Mitosis Animation
Name each stage as you see it occur
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Uncontrolled Mitosis
 If mitosis is not
controlled, unlimited
cell division occurs
causing cancerous
tumors
 Oncogenes are special
proteins that increase
the chance that a
normal cell develops
into a tumor cell
Cancer cells
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Mitosis in Onion Root Tips
Do you see any stages of mitosis?
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Meiosis
Formation of Gametes
(Eggs & Sperm)
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Facts About Meiosis
Occur after interphase which
includes chromosome replication
Two meiotic divisions
Meiosis I and Meiosis II
Original cell is diploid (2n)
Four daughter cells produced are
haploid (1n)
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Facts About Meiosis
Daughter cells contain half the
number of chromosomes as the
original cell
Produces gametes (eggs & sperm)
Occurs in the testes of males
(Spermatogenesis)
Occurs in the ovaries of females
(Oogenesis)
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Why Do we Need Meiosis?
It is the fundamental basis of
sexual reproduction
Two haploid (1n) gametes are
brought together through
fertilization to form a diploid
(2n) zygote
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Fertilization – “Putting it all
together”
2n = 6
1n =3
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Meiosis Forms Haploid Gametes
 Meiosis must reduce the chromosome number
by half
 Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right
number!
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Meiosis I: Reduction Division
Spindle
fibers
Nucleus
Early
Prophase I
Late
Prophase
I
Nuclear
envelope
Metaphase
Anaphase Telophase I
I
I
(diploid)
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Prophase I
Early prophase
Homologs pair up
Crossing over
occurs
Late prophase
Chromosomes condense
Spindle forms
Nuclear envelope
fragments
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Crossing-Over in Prophase I
Homologous chromosomes in a tetrad cross over each
other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring
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Metaphase I
Homologous pairs of chromosomes
align along the equator of the cell
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Anaphase I
Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.
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Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.
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Meiosis II: Reducing Chromosome
Number
Prophase
II
Metaphase
Telophase
II
Anaphase
4 Identical
II
II
haploid cells
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Prophase II
Nuclear envelope
(if it reformed)
disappears.
Spindle forms.
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Metaphase II
Chromosomes align
along equator of cell.
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Anaphase II
Equator
Pole
Sister chromatids
separate and move
to opposite poles.
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Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.
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Results of Meiosis
Gametes (egg & sperm) form
Four haploid cells with one
copy of each chromosome
One allele of each gene
Different combinations of
alleles for different genes
along the chromosome
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Gametogenesis
Oogenesis
or
Spermatogenesis
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Spermatogenesis
Occurs in the testes
Two divisions (Meiosis)
produce 4 spermatids
Spermatids mature
into sperm
Men produce about
250,000,000 sperm
per day
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Oogenesis
Occurs in the ovaries
Two divisions produce 3 polar bodies
that die and 1 egg
Polar bodies die because of unequal
division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte
matures into an ovum (egg) every 28
days
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Comparing
Mitosis and
Meiosis
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Comparison of Divisions
Mitosis
Meiosis
2
Number of divisions
1
Number of daughter
cells
2
4
Genetically identical?
Yes
No
Chromosome # Same as parent (2n) Half of parent (1n)
Where
Somatic cells
(Body cells)
Germ cells
(Sex cells)
When
Throughout life
At sexual maturity
Growth and repair
Sexual reproduction
Role
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