AP Biology

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AP Biology

• Chapter 12
• The Cell Cycle

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One cell becoming two
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Chromatin vs. Chromosomes appearance within the
cell.
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Fig 19.4Coiling up of Chromatin
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Somatic cells vs. Germ cellsThe egg surrounded
by sperm.
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Fig 12.4Before and after the S phase
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Mitosis (1 Division) vs.Meiosis (2 Divisions)
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Interphase
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Interphase cell (Look at the chromatin in the
blue nucleus and the yellow cytoskeleton.)
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Fig 12.6 a
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Cell in Prophase
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Fig 12.6 b
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Cell in Metaphase
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Cell in Anaphase
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Cell in Telophase and starting Cytokinesis
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LE 12-8b
Chromosome movement
Kinetochore
Tubulin subunits
Motor protein
Microtubule
Chromosome
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Animal vs. Plant
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LE 12-10
Chromatin condensing
Nucleus
10 µm
Chromosomes
Cell plate
Nucleolus
Prometaphase. We now see discrete chromosomes
each consists of two identical sister
chromatids. Later in prometaphase, the nuclear
envelope will fragment.
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.
Metaphase. The spindle is complete, and the
chromosomes, attached to microtubules at their
kinetochores, are all at the metaphase plate.
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.
Anaphase. The chromatids of each chromosome have
separated, and the daughter chromosomes are
moving to the ends of the cell as their
kinetochore micro- tubules shorten.
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Microscopic view of Mitosis in Onion root
tips.Can you identify the stages?
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LE 12-11_3
Cell wall
Origin of replication
Plasma membrane
E. coli cell
Bacterial chromosome
Chromosome replication begins. Soon thereafter,
one copy of the origin moves rapidly toward the
other end of the cell.
Two copies of origin
Origin
Origin
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.
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Checkpoints(Is all going according to plan?)
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LE 12-15
G0
G1 checkpoint
G1
G1
If a cell receives a go-ahead signal at the G1
checkpoint, the cell continues on in the cell
cycle.
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.
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LE 12-16a
G1
G2
S
M
S
M
G2
G1
M
MPF activity
Cyclin
Relative concentration
Time
Fluctuation of MPF activity and cyclin
concentration during the cell cycle
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LE 12-16b
G1
Cyclin
S
Cdk
M
Degraded cyclin
G2
accumulation
G2 checkpoint
Cdk
Cyclin is degraded
Cyclin
MPF
Molecular mechanisms that help regulate the cell
cycle
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LE 12-8b
Chromosome movement
Kinetochore
Tubulin subunits
Motor protein
Microtubule
Chromosome
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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).
25 µm
Normal mammalian cells
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LE 12-18b
Cancer cells do not exhibit anchorage
dependence or density-dependent inhibition.
25 µm
Cancer cells
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Malignant cancer cells from the breast(See the
ABNORMAL crab shape of the cells.)