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CELL CYCLE
CHAPTER 12
Figure 12.0 Mitosis
Figure 12.1a The functions of cell division: Reproduction
Figure 12.1b The functions of cell division: Growth and development
Figure 12.1c The functions of cell division: Tissue renewal
Figure 12.2 Eukaryotic chomosomes
Vocabulary
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Chromatin – long, thin fibers of DNA
wrapped around proteins
Chromosome – one long DNA
molecule; condensed and clearly visible
during cell division
Chromatid – two identical DNA
molecules attached by a centromere
(sister chromatids)
NEW VOCABULARY
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Centrosome – microtubule organizing
center which includes a pair of centrioles
 Centrosomes replicate in interphase and
move to opposite poles in prophase
Centromere – region where 2 chromatids
are attached to one another
Kinetochore – specialized region of
centromere where spindle fibers attach
Figure 12.3 Chromosome duplication and distribution during mitosis
CELL CYCLE
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Interphase
 G1 (first gap)
 S (DNA synthesis = chromosomes replicate)
 G2 (second gap)
Mitosis
 Prophase
 Metaphase
 Anaphase
 Telophase
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Cell Cycle Animation
Mitosis Animation
Figure 12.4 The cell cycle
Prophase
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Chromosomes visible
Centrosomes move towards opposite
poles and begin making spindle fiber
Nuclear membrane, nucleus, and
nucleolus disintegrate
Spindle fiber form and some attach to
the kinetochores of the centromeres
Metaphase
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Chromosomes line up at the
middle of the cell
Figure 12.6 The mitotic spindle at metaphase
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase;
prometaphase
Anaphase
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Sister chromatids are pulled apart
and move toward opposite ends of
the cell by the spindle fiber
Nonkinetochore spindle help
elongate the cell
Cell plate begins to form in plant
cells (immature cell wall)
Telophase
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Events are opposite those of prophase
Nuclear membranes, nuclei, and nucleoli
form in each new cell
Cytokinesis occurs – (cleavage forms)
Chromosomes unravel and become
chromatin again
Spindle fibers disintegrate
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase;
anaphase; telophase and cytokinesis.
Figure 12.5x Mitosis
Figure 12.8 Cytokinesis in animal and plant cells
Figure 12.9 Mitosis in a plant cell
Figure 12-09x Mitosis in an onion root
BINARY FISSION
Bacteria only have one
chromosome so steps of mitosis
are not needed
 Bacteria replicate via binary
fission
 DNA replicates at a specific
point (origin of replication)
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Figure 12.10 Bacterial cell division (binary fission) (Layer 1)
Figure 12.10 Bacterial cell division (binary fission) (Layer 2)
Figure 12.10 Bacterial cell division (binary fission) (Layer 3)
Evolution of Mitosis
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Prokaryotic and eukaryotic cell division share
some similar proteins that are involved in cell
division
Possible intermediates:
 Current examples in some protists
 Nuclear envelopes remain intact and
replicated chromosomes attach to
envelope
 As nucleus elongates, chromosome
separate
 Spindle forms inside nucleus
REGULATION OF CELL
CYCLE
Checkpoint – critical point in cell
cycle where process can stop or go
ahead according to signals
 Kinases – enzymes that can
activate or inactivate something
via phosphorylation
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Figure 12.13 Mechanical analogy for the cell cycle control system
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Restriction point – the most
critical of checkpoints
 During G1, if signaled to
proceed then cell usually
completes cell cycle and divides
 If no signal to proceed, cell
goes into nondividing state, G0
 Most cells are in G0
 Go signal means enter S and
replicate DNA
Cyclin is a protein that
activates kinases that are called
cyclin-dependent kinases or
Cdks
 MPF (maturation promoting
factor) – combination of Cdks
and cyclin
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Cyclins accumulate during G2 and
associate with Cdk’s to make MPF
 MPF initiates mitosis at G2
checkpoint by phosphorylating
various proteins
 Nuclear membrane is
phosphorylated and this causes
it to break down
 Proteolytic enzymes break down
MPF which helps end mitosis
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Figure 12.14 Molecular control of the cell cycle at the G2 checkpoint
M Phase Checkpoint
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M phase (metaphase checkpoint)
Kinetochores not attached yet to
spindle send delay signals to prevent
anaphase from starting too early.
Why must the cell wait for all of the
chromosomes to line up in the middle
of metaphase before proceeding to
anaphase?
OTHER SIGNALS
A signal that delays anaphase
so that right number of
chromosomes end up in each
new cell
 Growth factors – external
signals that can stimulate cell
division
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Density-dependent
inhibition – cells stop
dividing when crowded
 Anchorage-dependent –
most animal cells must be
attach to substratum
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Figure 12.16 Density-dependent inhibition of cell division
CANCER
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Cancer – cells that divide excessively
and invade other tissues
Metastasis – spread of cancer cells
Tumor – mass of abnormal cells
 Benign – cells stay “put”, not cancer
 Malignant – cells move (metastasis),
cancer
Figure 12.17 The growth and metastasis of a malignant breast tumor
Figure 12-17x1 Breast cancer cell
Figure 12-17x2 Mammogram: normal (left) and cancerous (right)