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AP Biology
Chapter 12:
The Cell Cycle
One cell becoming two
Chromatin vs. Chromosomes
appearance within the cell.
Fig: 19.4
Coiling up of Chromatin
Somatic cells vs. Germ cells
The egg surrounded by sperm.
Fig: 12.4
Before and after the S phase
Mitosis (1 Division) vs.
Meiosis (2 Divisions)
Interphase
Interphase cell
(Look at the chromatin in the blue nucleus and the
yellow cytoskeleton.)
Fig: 12.6 a
Cell in Prophase
Fig: 12.6 b
Cell in Metaphase
Cell in Anaphase
Cell in Telophase and starting
Cytokinesis
LE 12-8b
Chromosome
movement
Microtubule
Motor
protein
Chromosome
Kinetochore
Tubulin
subunits
Animal vs. Plant
LE 12-10
Nucleus
Nucleolus
Chromatin
condensing
Prophase. The
chromatin is condensing.
The nucleolus is
beginning to disappear.
Although not yet visible
in the micrograph, the
mitotic spindle is starting
to form.
Chromosomes
Prometaphase. We
now see discrete
chromosomes; each
consists of two identical
sister chromatids. Later
in prometaphase, the
nuclear envelope will
fragment.
Cell plate
Metaphase. The spindle is
complete, and the
chromosomes, attached
to microtubules at their
kinetochores, are all at
the metaphase plate.
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends of
the cell as their
kinetochore microtubules shorten.
10 µm
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will divide
the cytoplasm in two, is
growing toward the
perimeter of the parent
cell.
Microscopic view of Mitosis in Onion root tips.
Can you identify the stages?
LE 12-11_3
Cell wall
Origin of
replication
E. coli cell
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.
Plasma
membrane
Bacterial
chromosome
Two copies
of origin
Origin
Origin
Checkpoints
(Is all going according to plan?)
LE 12-15
G0
G1 checkpoint
G1
If a cell receives a go-ahead
signal at the G1 checkpoint,
the cell continues on in the
cell cycle.
G1
If a cell does not receive a
go-ahead signal at the G1
checkpoint, the cell exits the
cell cycle and goes into G0, a
nondividing state.
LE 12-16a
M
G1
S
G2
M
G1
S
G2
M
MPF activity
Cyclin
Time
Fluctuation of MPF activity and cyclin concentration
during the cell cycle
LE 12-16b
Cdk
Degraded
cyclin
G2
checkpoint
Cyclin is
degraded
MPF
Cdk
Cyclin
Molecular mechanisms that help regulate the cell cycle
LE 12-8b
Chromosome
movement
Microtubule
Motor
protein
Chromosome
Kinetochore
Tubulin
subunits
LE 12-18a
Cells anchor to dish surface and
divide (anchorage dependence).
When cells have formed a complete
single layer, they stop dividing
(density-dependent inhibition).
If some cells are scraped away, the
remaining cells divide to fill the gap and
then stop (density-dependent inhibition).
Normal mammalian cells
25 µm
LE 12-18b
Cancer cells do not exhibit
anchorage dependence
or density-dependent inhibition.
25 µm
Cancer cells
Malignant cancer cells from the breast
(See the ABNORMAL “crab” shape of the cells.)