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Chapter 12
Cell Cycle and Mitosis
Overview
Key Roles of Cell Division
1. Continuity of life is based on reproduction of
cells, or cell division
2. Asexual reproduction of an entire organism; ex:
an amoeba is a one celled organism.
3. Production of progeny from multicellular
organisms. Ex: plant cuttings
4. Sexually reproducing organisms from single cell
(fertilized egg  fetus  infant)
5. Renewal & repair of damaged or worn out cells
amoeba
Cell Division Roles
• Prokaryotic cells
– Binary fission = reproduction
– Origin of Replication = point where
replication begins in bacteria DNA
• Eukaryotic cells
– Development, growth, and repair
Binary Fission
in Prokaryotes
Chromosome
replication begins.
Soon thereafter,
one copy of the origin
moves rapidly toward
the other end of the cell.
Replication continues.
One copy of the origin
is now at each end of
the cell.
Replication finishes.
The plasma membrane
grows inward, and
new cell wall is
deposited.
Two daughter
cells result.
Cell wall
Origin of
replication
E. coli cell
Plasma
membrane
Bacterial
chromosome
Two copies
of origin
Origin
Origin
Cell cycle
• Cell has a “life cycle”~24 hours
cell is formed from
a mitotic division
cell grows & matures
to divide again
G1, S, G2, M
epithelial cells,
blood cells,
stem cells
cell grows & matures
to never divide again
liver cells
G1G0
brain / nerve cells
muscle cells
Interphase
(90% of cell life is spent in this phase) G1- S – G2
- Nucleus well-defined
– DNA loosely packed in long
chromatin fibers
•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
- makes more organelles,
proteins, membranes
Mitotic Chromosome
 Duplicated chromosome
2 sister chromatids
 narrow at centromeres
 contain identical
copies of original DNA

homologous
chromosomes
homologous
chromosomes
single-stranded
sister chromatids
double-stranded
homologous = “same information”
Mitosis
• Dividing cell’s DNA between
2 daughter nuclei
• 5 phases
–
–
–
–
–
Prophase
prometaphase
metaphase
anaphase
telophase
Mitotic
Division
- Duplicate nuclear
material
- Produce identical
daughter cells
(diploid)
- Asexual reproduction:
clones produced
- Maintains
chromosomal number
- Somatic/Autosomal/
Body Cells
(repair/replace)
Cytokinesis
• Animals
– form a cleavage furrow
– constriction belt of actin
microfilaments around
equator of cell
• splits cell in two
• like tightening a belt around
a balloon
Cytokinesis in Plants
Cell plate
• vesicles (derived from
Golgi) line up at
equator
• vesicles fuse to form
new cell wall
Control of cell division
• How do cells know when to divide?
– The frequency of cell division varies with each type of
cell
– cell communication signals
• chemical signals in cytoplasm give cue
• Cell cycle has check points
• signals usually mean proteins
– Activator proteins
– Inhibitor Proteins
Control of the Cell Cycle:
a molecular control system
• The frequency of cell division varies with the type
of cell
• Cell cycle is regulated at the molecular level
• Cell cycle is driven by
specific chemical signals
present in the cytoplasm
• The cell cycle has
specific checkpoints
where the cell cycle stops
until a go-ahead signal is
received
Control of Cell Cycle
G1 checkpoint seems to be the most important
• If a cell receives a go-ahead signal at the G1
checkpoint, it will usually complete the S, G2, and
M phases and divide
• If the cell does not
receive the go-ahead
signal, it will exit the
cycle, switching into a
nondividing state
called the G0 phase
(ex: muscle and
nervous system cells)
Internal signals
• Cell cycle controls:
cyclins
regulatory proteins
level cycle in the cell
Cdks
Cyclin-dependent kinases
Phosphorylate cellular proteins
(activates or inactivates proteins)
Cdk-cyclin complex (MPF-maturation promoting
Factor)
triggers passage through
different stages of cell cycle
• Cdk-cyclin levels fluctuate with each phase
External signals
• Growth factors
Protein signals released by body cells
that stimulate other cells to divide
For example, platelet-derived growth factor
(PDGF) made by platelets in blood clots stimulates
cell division in connective tissue -- heal wounds
• Density-dependent inhibition
crowded cells stop dividing
• Anchorage dependence
to divide cells must be attached to a
substrate
Proto-oncogene to Oncogene
Tumor Suppressor Genes
• HeLa Cell video
Another Hela Cells Video
https://www.youtube.com/watch?v
=MWHfifbXkdk
ASEXUAL REPRODUCTION
Bacteria reproduce using
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html
BINARY FISSION
__________________________________
http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.13.2.hydra.jpg
Budding & regeneration are used by plants
and animals to reproduce asexually
(mitosis)
Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm
BINARY FISSION & MITOSIS
identical
Produces cells that are __________
copies of parent cell
ADVANTAGES OF
ASEXUAL REPRODUCTION
Can make offspring
faster
Don’t need a partner
http://www.mrgrow.com/images/cutting.jpg
DISVANTAGES OF
ASEXUAL REPRODUCTION
ALL ALIKE
Species CAN’T
change and adapt
One disease can wipe
out whole population
http://www.mrgrow.com/images/cutting.jpg
Chapter 13
Meiosis
Meiosis
• Division of germ cells aka gametes (sperm and
egg)
• Used for sexual reproduction
• Goes through I-PMATC-PMATC (2 Divisions
called Meiosis I and Meiosis II)
• Produces 4 genetically different daughter cells
with half the number of chromosomes
(haploid)
•
•
Haploid- n- one copy of the homologous pair
Diploid- 2n- both copies of the homologous pair
SEXUAL REPRODUCTION
Family image from: http://babyhearing.org/Parenet2Parent/index.asp
Combines genetic material
from 2 parents (sperm & egg)
Offspring are genetically
different from parents
ADVANTAGES OF
SEXUAL REPRODUCTION
Allows for variation in population
Individuals can be different
Provides foundation for EVOLUTION
Allow species adapt to
changes in
their environment
http://naturalsciences.sdsu.edu/classes/lab8/spindex.html
Image by Riedell
EGG
Image by Riedell
+
http://www.angelbabygifts.com/
SPERM 
If egg and sperm had same number of
chromosomes as other body cells . . .
baby would have too many chromosomes!
http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg
MEIOSIS is the way…
http://waynesword.palomar.edu/lmexer2a.htm
to make cells
with ½ the
number of
chromosomes
for sexual
reproduction
• Each human somatic cell is diploid (any cell other
than a gamete) has 46 chromosomes arranged in
pairs
• A karyotype is an ordered display of the pairs of
chromosomes from a cell
• The two chromosomes in each pair are called
homologous chromosomes, or homologues
• Both chromosomes in a pair carry genes controlling
the same inherited characteristics
• Sex chromosomes/gametes: X and Y
• Non sex: 22 pairs of autosomes
• Females: XX
Males: XY
Karyotype Images
Male Karyotype
Female Karyotype
Chromosomes in Human Cells – Cont.
• Each pair of homologous chromosomes includes one
chromosome from each parent
• The 46 chromosomes in a human somatic cell are
two sets of 23: one from mom and one dad
• The number of chromosomes in a single set is
represented by n. It’s called haploid
• A cell with two sets is called diploid (2n)
• For humans, the diploid number is 46 (2n = 46)
• In a cell in which DNA synthesis has occurred, each
chromosome is replicated and consists of 2
identical sister chromatids
MITOSIS
• Makes ___
2 cells genetically
identical
_________
to parent cell &
to each other
2n
• Makes ___ cells
• Makes __________
SOMATIC (body)
• Used by organisms to:
increase size of organism,
repair injuries,
replace worn out cells
http://waynesword.palomar.edu/lmexer2a.htm
MEIOSIS
4 cells
• Makes ____
genetically different from
parent cell & from each
other
1n cells
• Makes _____
• Makes ______________
Germ cells
OR Gametes (sperm & eggs)
• Used for ____________
sexual
reproduction
http://waynesword.palomar.edu/lmexer2a.htm
Gametogenesis- process of
forming games (n) from diploid
(2n) cells
• Spermatogenesis
• Oogenesis
Figure 11-15 Meiosis
Meiosis I:
Section 11-4
Homologous chromosomes separate
Results in two haploid daughter cells with replicated
chromosomes
Meiosis II: Figure 11-17 Meiosis II
Sister chromatids separate
Section 11-4
Results in four haploid daughter cells with unreplicated
chromosomes
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Genetic Variability comes from:
1) Segregation(Ana I)
• Crossing Over (Pro I)
2) Independent Assortment
3) Random Fertilization
MITOSIS vs MEIOSIS
INTERPHASE INTERPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA is spread out as chromatin
• Nuclear membrane/
nucleolus visible
• DNA is copied during S phase
• Makes stuff new cell needs in G2
SAME AS
MITOSIS
MITOSIS vs MEIOSIS
PROPHASE PROPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
DNA scrunches into
chromosomes
Nuclear membrane/
nucleolus disappear
Centrioles/
spindle fibers appear
DNA scrunches into
chromosomes
Nuclear membrane/
nucleolus disappear
Centrioles/
spindle fibers appear
Homologous pairs match up
MITOSIS vs MEIOSIS
METAPHASE
METAPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• Chromosomes line up
in middle
Chromosomes line up
in middle
with homologous partner
MITOSIS vs MEIOSIS
ANAPHASE ANAPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
APART:
Chromatids split
APART:
Chromatids stay together
Homologous pairs split
MITOSIS vs MEIOSIS
TELOPHASE TELOPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
See TWO nuclei
Nuclear membrane/
SAME AS MITOSIS
nucleolus return
DNA spreads out as chromatin
Spindle/centrioles disappear
MITOSIS vs MEIOSIS
CYTOKINESIS CYTOKINESIS I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Cytoplasm splits
into 2 cells
SAME AS
MITOSIS
MITOSIS vs MEIOSIS
INTERPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA is spread out as chromatin
SKIP
• Nuclear membrane/
INTERPHASE II
nucleolus visible
• DNA is copied during S phase DNA NOT COPIED
(No S phase)
MITOSIS vs MEIOSIS
PROPHASE PROPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA scrunches into
chromosomes
• Nuclear membrane/
nucleolus disappear
• Centrioles/
spindle fibers appear
SAME AS MITOSIS
MITOSIS vs MEIOSIS
METAPHASE
METAPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• Chromosomes line up
in middle
SAME AS MITOSIS
MITOSIS vs MEIOSIS
ANAPHASE ANAPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Chromatids split and
move apart
SAME AS MITOSIS
MITOSIS vs MEIOSIS
TELOPHASE TELOPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Two nuclei
Nuclear membrane/
nucleolus returns
Centrioles/spindle fibers
disappear
DNA spreads out as
chromatin
Diploid nuclei
SAME AS MITOSISexcept 4 haploid nuclei
MITOSIS vs MEIOSIS
CYTOKINESIS CYTOKINESIS II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Cytoplasm splits
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
SAME AS MITOSIS
Ways Meiosis is different?
• Homologous pairs match up & trade DNA
(SYNAPSIS & CROSSING OVER) in
PROPHASE I
•SEGREGATION
& INDEPENDENT ASSORTMENT
in Anaphase I
create genetic recombination
• Skipping INTERPHASE II(Dividing TWICE but copying DNA once)
produces 1n cells
A Comparison of Mitosis and Meiosis
• Mitosis conserves the number of chromosome sets,
producing cells that are genetically identical to the
parent cell
• Meiosis reduces the number of chromosomes sets
from two (diploid) to one (haploid), producing cells
that differ genetically from each other and from the
parent cell
Property
Mitosis
Meiosis
DNA
replication
Divisions
During
interphase
One
During
interphase
Two
Synapsis and
crossing over
Daughter cells,
genetic
composition
Do not occur
Role in animal
body
Produces cells
for growth and
tissue repair
Form tetrads in
prophase I
Four haploid,
different from
parent cell and
each other
Produces
gametes
Two diploid,
identical to
parent cell
ALTERNATION OF GENERATIONS
IN PLANTS AND SOME ALGAE:
SPOROPHYTE =
____________
multicellular diploid stage in which meiosis
SPORES
makes haploid cells called _________
Spores give rise to
a multicellular
HAPLOID organism
GAMETOPHYTE
= ________________
without fusing
with another cell
Image from Biology Campbell and Reece
IN FUNGI and SOME PROTISTS:
Gametes fuse to make a diploid zygote
Meiosis occurs in zygote without
growing into a diploid organism
Meiosis makes
haploid cells that
grow into haploid
organisms which use
MITOSIS to make
GAMETES!
Image from Biology Campbell and Reece