Download The Cell Cycle (2009).

The Cell Cycle
Biology B/DNA and the Cell Cycle
Limits to Cell Growth
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As living organisms grow, so do their cells.
As cells get larger, eventually they must
divide for two reasons:
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DNA overload: As a cell gets large, its DNA
cannot hold all the information necessary for the
cell to run properly.
Movement of materials: Materials have to travel
too far to get from the cell membrane to the
nucleus. The cell becomes inefficient.
Preparing for Cell Division
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As cells prepare for division the DNA that
was loose in the nucleus folds into
chromosomes.
The Cell Cycle
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At any given time in a cell’s life it is either
dividing or not dividing.
The periods of time when cells are not
dividing are called Interphase.
The periods of time when cells are dividing
is referred to as the M phase.
Interphase
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There are three important things that
happen during Interphase:
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Cell Growth
DNA Replication (in preparation for cell division)
Preparation for the M phase
Interphase usually lasts longer than the M
phase
Interphase
M Phase
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The “M” in M phase stands for Mitosis,
which is the process of cell division.
Mitosis is divided into four phases that
happen one after the other:
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Prophase
Metaphase
Anaphase
Telophase
Prophase
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Prophase is the longest of the phases of
mitosis.
Chromosomes appear during prophase.
Centrioles (two tiny organelles in animal
cells) move away from the nuclear
envelope and towards opposite ends of the
cell and a spindle (fiber) forms between
them
The nuclear envelope breaks down.
Prophase
Metaphase
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Metaphase lasts only a few minutes.
The centromeres of the chromosomes
attach to the spindles in the center of the
cell.
Metaphase
Anaphase
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Sister chromatids (that make up the
chromosomes) separate and move along
the spindles to opposite sides of the cell.
The chromatids now become individual
chromosomes
Anaphase ends when the chromosomes
stop moving.
Anaphase
Telophase
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Telophase is the final phase of mitosis
The chromosomes unfold into loose
groupings of DNA.
Nuclear envelopes re-form around the DNA
at each end of the cell.
The spindle breaks down.
Telophase
Cytokinesis
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There is one last part to the M phase and
the completion of cell division.
During cytokinesis the cytoplasm splits to
form two separate cells.
In animal cells, the cytoplasm actually splits
off.
In plant cells a cell plate forms in the middle
of the dividing cell.
Cytokinesis