Chapter 8. The Cell Cycle. The Life of a Eukaryotic Cell. The ability of organisms to reproduce best distinguishes living things from nonliving matter The continuity of life is based upon the reproduction of cells, or cell division.
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The Cell Cycle
Growth and development
Somatic (nonreproductive, also called autosomal) cells have two complete sets of chromosomes
Mitosis, the division of the nucleus
Cytokinesis, the division of the cytoplasm
Gametes are produced by a variation of cell division called meiosis
Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cellPhases of Cell Cycle
G2 OF INTERPHASE
TELOPHASE AND CYTOKINESIS
Video: Sea Urchin (time lapse)
Animation: Mitosis (All Phases)
Animation: Mitosis Overview
Animation: Late Interphase
now see discrete chromosomes; each
consists of two identical sister chromatids. Later
in prometaphase, the
nuclear envelope will fragment.
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.
chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro-
Contractile ring of
Cleavage of an animal cell (SEM)
New cell wall
Cell plate formation in a plant cell (TEM)
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.
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
Fluctuation of MPF activity and cyclin concentration
during the cell cycle
Molecular mechanisms that help regulate the cell cycle
Cells anchor to dish surface and
divide (anchorage dependence).
When cells have formed a complete
single layer, they stop dividing
If some cells are scraped away, the
remaining cells divide to fill the gap and
then stop (density-dependent inhibition).
Normal mammalian cells
Cancer cells do not exhibit
or density-dependent inhibition.
A small percentage
of cancer cells may
survive and establish
a new tumor in another
part of the body.
Cancer cells invade
A tumor grows from a
single cancer cell.
Cancer cells spread
through lymph and
blood vessels to
other parts of the