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 – cell grows)
 S (DNA synthesis = chromosomes replicate)
 G2 (second gap – cell grows)
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 and Cytokinesis
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Events are opposite those of prophase
Nuclear membranes, nuclei, and nucleoli
form in each new cell
Chromosomes unravel and become
chromatin again
Spindle fibers disintegrate
Cytokinesis occurs – formation of
cleavage
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 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
Checkpoints – critical points 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 or G1 checkpoint –
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)
MEIOSIS
CHAPTER 13
REPRODUCTION
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Asexual reproduction – single
parent passes on all of its genes to
its offspring
Sexual reproduction – two
parents give rise to offspring that
have a combination of genes
inherited from two parents
Figure 13.1 The asexual reproduction of a hydra
VOCABULARY
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Karyotype – picture of an
organisms chromosomes
Homologous chromosomes – pair
of similar chromosomes
Haploid – single chromosome set
(n=23 for humans)
Diploid – two sets of chromosomes
(2n=46 for humans)
Zygote – fertilized egg
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Fertilization or syngamy – fusion of sperm
and egg
Somatic cell – body cells
Gametes – sex cells
Sex chromosomes – determine gender
Autosomes – all other chromosomes
Sister chromatids – copies of same
chromosome
HUMAN FEMALE
HUMAN MALE
Figure 13.x1 SEM of sea urchin sperm fertilizing egg
Figure 13.4 The human life cycle
MEIOSIS
A process that halves the
chromosome number
 Mitosis vs. Meiosis
 Genetic recombination
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Figure 13.6 Overview of meiosis
Figure 13.7 Meiosis I
Figure 13.7 Meiosis II
Figure 13.8 Mitosis vs. Meiosis
Figure 13.8 Mitosis vs. Meiosis
Figure 13.9 Different possible sex cells
(Independent Assortment of Chromosomes)
MORE GENETIC
POSSIBILITIES
Synapsis – pairing of
homologous chromosomes in
prophase I
 Chiasmata or crossing over–
when homologous portions of
two nonsister chromatids trade
place
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Figure 13.10 Crossing over during meiosis