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Chapter 12: The Cell Cycle:
Cell Growth, Cell Division
AP Biology
Why do cells divide?
 For reproduction

asexual reproduction
 one-celled organisms
 For growth

from fertilized egg to
multi-celled organism
 For repair & renewal

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replace cells that die
from normal wear &
tear or from injury
amoeba
Sexual Reproduction
Getting from there to here…
 Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
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Asexual Reproduction on a Large Scale
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Chromosome numbers in somatic and
gamete cells
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Both Binary Fission and Mitosis
Produce Genetically Identical Cells
 Four events must occur for cell division:
• Reproductive signal—to initiate cell
division
• Replication of DNA
• Segregation—distribution of the DNA
into the two new cells
• Cytokinesis—division of the cytoplasm
and separation of the two new cells
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Binary Fission
In prokaryotes, cell
division results in
reproduction of the
entire organism.
Two important regions in reproduction:
•ori - where replication starts
•ter - where replication ends
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In Eukaryotes: Cell division results in genetically
identical daughter cells
 What is passed on to daughter cells?

exact copy of genetic material = DNA
 mitosis

organelles, cytoplasm, cell membrane,
enzymes
 cytokinesis
chromosomes (stained orange)
in kangaroo rat epithelial cell
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notice cytoskeleton fibers
Copying DNA & packaging it…
 After DNA duplication, chromatin condenses

coiling & folding to make a smaller package
mitotic chromosome
DNA
chromatin
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0.5 µm
Chromosomes
Chromosome arm
DNA molecules
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Separation of
sister chromatids
Centromere
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Sister chromatids
Interphase
 90% of cell life cycle

cell doing its “everyday job”
 produce RNA, synthesize proteins/enzymes

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prepares for duplication if triggered
Overview of mitosis
interphase
prophase
I.P.M.A.T.
(pro-metaphase)
cytokinesis
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metaphase
anaphase
telophase
Cell cycle
 Cell has a “life cycle”
cell is formed from
a mitotic division
cell grows & matures
to divide again
G1, S, G2, M
epithelial cells,
blood cells,
stem cells
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cell grows & matures
to never divide again
liver cells
G1G0
brain / nerve cells
muscle cells
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
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G0
green = key features
Interphase
 Nucleus well-defined

DNA loosely packed in
long chromatin fibers
 Prepares for mitosis

replicates
chromosome
 DNA & proteins

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produces proteins &
organelles
S phase: Copying / Replicating DNA
 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)
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ACTGGTCAGGCAATGTC
Organizing DNA
DNA
 DNA is organized in
chromosomes
histones
double helix DNA molecule
 wrapped around histone
proteins

 like thread on spools

DNA-protein complex =
chromatin
chromatin
 organized into long thin fiber

condensed further during
mitosis
double stranded chromosome
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duplicated mitotic chromosome
doublestranded
mitotic human
chromosomes
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Mitosis
 Dividing cell’s DNA between
2 daughter nuclei
 4 phases
prophase
 metaphase
 anaphase
 telophase

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Chromosome movement
 Kinetochores use
motor proteins that
“walk” chromosome
along attached
microtubule

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microtubule
shortens by
dismantling at
kinetochore
(chromosome) end
green = key features
Telophase
 Chromosomes arrive at
opposite poles
daughter nuclei form
 chromosomes disperse

 no longer visible under
light microscope
 Spindle fibers disperse
 Cytokinesis begins

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cell division
Cytokinesis
 Animals

constriction belt of
actin microfilaments
around equator of cell
 cleavage furrow forms
 splits cell in two
 like tightening a draw
string
Plant Cell Division Real Time Video
Animal Cell Division Video
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Cytokinesis in Animals
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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 between
membranes
 new cell wall fuses
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with existing cell wall
Cytokinesis in plant cell
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onion root tip
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Evolution of mitosis
 Mitosis in
chromosome:
double-stranded replication
of DNA
DNA
eukaryotes
likely evolved from
binary fission in
bacteria
single circular
chromosome
 no membranebound organelles

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Origin of
replication
elongation of cell
ring of
proteins
cell pinches
in two
Coordination of cell division
 A multicellular organism needs to
coordinate cell division across different
tissues & organs
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GHOSTS
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Mitosis in animal cells
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Mitosis in plant cell
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All Sexual Life
Cycles Involve
Fertilization and
Meiosis
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Haplontic life cycle
in protists, fungi, and some algae—
zygote is the only diploid stage
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Diplontic life cycle—animals
and some plants; gametes are
the only haploid stage
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green = key features
Prophase
 Chromatin condenses

visible chromosomes
 chromatids
 Centrioles move to opposite

poles of cell
Protein fibers cross cell to form
mitotic spindle


microtubules
coordinates movement of
chromosomes
 Nucleolus disappears
 Nuclear membrane breaks down
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green = key features
Transition to Metaphase
 Prometaphase

spindle fibers attach to
centromeres
 creating kinetochores

microtubules attach at
kinetochores
 connect centromeres to
centrioles

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chromosomes begin
moving
green = key features
Metaphase
 Chromosomes align
along middle of cell

metaphase plate
 meta = middle
spindle fibers coordinate
movement
 helps to ensure
chromosomes separate
properly

 so each new nucleus
receives only 1 copy of
each chromosome
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Separation of chromatids
 In anaphase, proteins holding together sister
chromatids are inactivated

separate to become individual chromosomes
1 chromosome
2 chromatids
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double-stranded
2 chromosomes
single-stranded
green = key features
Anaphase
 Sister chromatids separate at
kinetochores
move to opposite poles
 pulled at centromeres
 pulled by motor proteins
“walking”along microtubules

 increased production of
ATP by mitochondria
 Poles move farther apart

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polar microtubules lengthen