AP Biology 2007-2008
Chapter 12
The Cell Cycle:
Cell Growth, Cell Division
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Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
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And now look at you…
How did you get from there
to here?
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Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
Getting from there to here…
AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.5
Metabolic requirements also set an upper limit
to the size of a single cell.
As a cell increases in size its volume
increases faster (X3)than its surface area (X2).
Smaller objects have a greater ratio of
surface area to volume.
Cell membrane cannot keep up with the
nutrient supply needed by an enlarging
cytoplasm…. The solution to the problem is
to split into two cells.
Why do cells divide?
AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.5
Why do cells divide?
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For reproduction
asexual reproduction
one-celled organisms
For growth
from fertilized egg to
multi-celled organism
For repair & renewal
replace cells that die
from normal wear &
tear or from injury
What are the benefits
of Cell Division?
amoeba
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Making new cells
Nucleus
chromosomes
DNA
Cytoskeleton
centrioles
in animals
microtubule
spindle fibers
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nuclear pores
nuclear pore
nuclear envelope
nucleolus
histone protein
chromosome
DNA
Function
protects DNA
Structure
nuclear envelope
double membrane
membrane fused in spots to create pores
allows large macromolecules to pass through
Nucleus
What kind of molecules need to
pass through?
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Cytoskeleton
Function
structural support maintains shape of cell
provides anchorage for organelles
protein fibers
microfilaments, intermediate filaments, microtubules
motility cell locomotion
cilia, flagella, etc.
regulation
organizes structures
& activities of cell
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actin
microtubule
nuclei
Cytoskeleton
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Centrioles
Cell division
in animal cells, pair of centrioles organize microtubules spindle fibers
guide chromosomes in mitosis
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Getting the right stuff
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
notice cytoskeleton fibers
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Overview of mitosis
interphase prophase (pro-metaphase)
metaphase anaphase telophase
cytokinesis
I.P.M.A.T.
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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!
Checkpoints
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The distinct events of the cell cycle are
directed by a distinct cell cycle control
system.
These molecules trigger and coordinate key
events in the cell cycle.
The control cycle has
a built-in clock, but it
is also regulated by
external adjustments
and internal controls.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.13
Password
please!
MPF
please!
Chromatids Attached?
Than activate the APC!
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A checkpoint in the cell cycle is a critical
control point where stop and go signals
regulate the cycle.
Three major checkpoints are found in the:
G1 , G2, and M phases.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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For many cells, the G1 checkpoint, the
restriction point in mammalian cells, is the
most important.
If the cells receives a go-ahead signal, it
usually completes the cell cycle and divides.
If it does not receive a go-ahead signal, the cell
exits the cycle and switches to a nondividing
state, the G0 phase.
Most human cells are in this phase.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Read the ppt “Regulation of the Cell Cycle”
for details!
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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
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
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Interphase
Nucleus well-defined
DNA loosely packed in long chromatin fibers
Prepares for mitosis
replicates chromosome
DNA & proteins
produces proteins & organelles
green = key features
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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 in chromosomes 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 http://www.dnalc.org/
resources/3d/DNAWr
apAdvanced06.html
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Copying DNA & packaging it…
After DNA duplication, chromatin condenses
coiling & folding to make a smaller package
DNA
chromatin
mitotic chromosome
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double-stranded mitotic human chromosomes
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Mitotic Chromosome Duplicated chromosome
2 sister chromatids
narrow at centromeres
contain identical
copies of original DNA homologous
chromosomes homologous
chromosomes
sister chromatids homologous = “same information”
single-stranded double-stranded
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Mitosis
Dividing cell’s DNA between
2 daughter nuclei
“dance of the chromosomes”
4 phases
prophase
metaphase
anaphase
telophase
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Prophase Chromatin condenses
visible chromosomes chromatids
Centrioles move to opposite poles of cell
animal cell
Protein fibers cross cell to form mitotic spindle
microtubules
actin, myosin
coordinates movement of chromosomes
Nucleolus disappears
Nuclear membrane breaks down
green = key features
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Transition to Metaphase Prometaphase
spindle fibers attach to
centromeres
creating kinetochores
microtubules attach at
kinetochores
connect centromeres to centrioles
chromosomes begin moving
Nuclear envelope dissolves
green = key features
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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
green = key features
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Anaphase
Sister chromatids separate at
kinetochores
move to opposite poles
pulled at centromeres
pulled by motor proteins
“walking”along microtubules
actin, myosin
increased production of
ATP by mitochondria
Poles move farther apart
polar microtubules lengthen
green = key features
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Separation of chromatids
In anaphase, proteins holding together sister
chromatids are inactivated
separate to become individual chromosomes
2 chromosomes 1 chromosome
2 chromatids single-stranded
double-stranded
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Kinetochores use
motor proteins that
“walk” chromosome
along attached
microtubule
microtubule
shortens by
dismantling at
kinetochore
(chromosome) end
Chromosome movement
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Telophase
Chromosomes arrive at opposite poles
daughter nuclei form
nucleoli form
chromosomes disperse
no longer visible under light microscope
Spindle fibers disperse
Cytokinesis begins
cell division
green = key features
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Cytokinesis
Animals
constriction belt of
actin microfilaments
around equator of cell
cleavage furrow forms
splits cell in two
like tightening a draw
string
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Cytokinesis in Animals
The Stages of Mitosis
http://www.youtube.com/watch?v=VGV3fv-uZYI
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Mitosis in whitefish blastula
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Mitosis in animal cells
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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
with existing cell wall
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Cytokinesis in plant cell
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Mitosis in plant cell
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onion root tip
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Origin of replication
chromosome: double-stranded
DNA replication
of DNA
elongation of cell
cell pinches in two
ring of proteins
Evolution of mitosis
Mitosis in
eukaryotes
likely evolved from
binary fission in
bacteria
single circular
chromosome
no membrane-
bound organelles
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Evolution of
mitosis
A possible
progression of
mechanisms
intermediate
between binary
fission & mitosis
seen in modern
organisms
protists
dinoflagellates
protists
diatoms
eukaryotes
yeast
eukaryotes
animals
prokaryotes
(bacteria)
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Dinoflagellates
algae
“red tide”
bioluminescence
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Diatoms
microscopic algae
marine
freshwater
AP Biology 2007-2008
Any Questions??
AP Biology 2007-2008
Ghosts of Lectures Past
(storage)
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Control of Cell Cycle
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Kinetochore
Each chromatid
has own kinetochore
proteins
microtubules
attach to
kinetochore
proteins
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nucleosome DNA
histone
DNA double helix chromosome
rosettes of chromatin loops
scaffold protein
chromatin loop
Chromosome structure
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G2
S G1
M
metaphase
prophase
anaphase
telophase
interphase (G1, S, G2 phases)
mitosis (M)
cytokinesis (C)
C
Phases of a dividing cell’s life
interphase cell grows
replicates chromosomes
produces new organelles, enzymes, membranes…
G1, S, G2
mitotic phase cell separates & divides chromosomes mitosis
cell divides cytoplasm & organelles cytokinesis
Cell Division cycle
AP Biology 2007-2008
Substitute Slides
for Student Print version
(for student note-taking)
AP Biology
How did you
get from there
to here?
And now look at you…