Download Mitosis and the Cell Cycle

Mitosis and the Cell Cycle
DAY C
01/03/07
Objectives:
Define
the cell cycle.
Describe the four phases of the
cell cycle and mitosis.
The Cell Cycle
In most animal and plant cells the cells
increase in size and then they divide into
two cells.
 Then the new cells increase in size and
divide again.
 This occurs repeatedly to create new
cells.
 This is called the Cell Cycle.

Differences in cell division between
prokaryotes and eukaryotes
Prokaryotes
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Less complex cells; so
division is fairly simple.
In division one cell divides
into two daughter cells.
Must replicate genetic
material and separate it into
the two daughter cells.
Does not go through the
complex steps of cell
division; can just divide in
two after genetic material is
replicated.
Eukaryotes

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More complex cells; so
division is more complex.
Must replicate
chromosomes and make
sure they separate properly.
Goes through similar
process of prokaryotes
only more complex.
Goes through the steps of
mitosis.
Cell Cycle Stages

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The cell cycle is the period of time from the
beginning of one cell division to the beginning
of the next.
What happens during the cell cycle?
– The cells doubles its contents so it can
divide into two independent cells.
What are the stages of the cell cycle?
– G, S, and M phases
The Cell Cycle Stages

What happens in each stage?
– G phases (G1 and G2) - Growth phases; the cell
grows most in G1 but it will also grow a little in G2.
– S phase – synthesis phase; the cell’s DNA
replicates so that it has twice the amount of DNA
(and chromosomes) as a normal cell would.
– M phase – cell division phase; mitosis occurs in this
phase and the cell finally splits into two independent
“daughter” cells.
What is the order of the Cell Cycle?
Timing of the Cell Cycle Stages

Not all cells move through the cell cycle
at the same rate.
– Cells in an embryo can go through the
cell cycle in as little as 30 minutes.
– Average cells in an adult human go
through the cell cycle in about 20
hours.
Interphase
Interphase is made up of all stages of the
cell cycle except mitosis (M Phase).
 In interphase the DNA and protein that
make up chromosomes are unfolded and
the most active, using the information
they contain to direct cell growth and
development.

Mitosis (The M Phase)
You observed the four different stages of
mitosis, as well as the interphase stage
of the cell cycle.
 The four stage of mitosis are: prophase,
metaphase, anaphase, and telophase.

Prophase

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The first phase of mitosis;
it generally takes longer
than the rest.
First clue that prophase
has begun is that the
chromosomes become
visible.
Chromosomes are made of
two identical strands called
chromatids (sister
chromatids).
The chromatids are
attached to the
centromere.
Metaphase

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The second stage of
mitosis.
They complete their
attachment to the
spindle fibers and line up
across the middle of the
cell.
Anaphase

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The centromeres that
hold the chromatids
together split.
The chromatids move
toward the two poles of
the cell; thus separating
the duplicated
chromosomes.
Telophase

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The microtubules of the
spindle begin to break
apart.
The chromosomes
clustered at either pole
of the cell spread out.
Nuclear membrane
forms around each
cluster of chromosomes.
Cytokinesis

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Process where the
cytoplasm divides in half.
Occurs along with
telophase and results in
two separate daughter
cells.
Cytokinesis in Plant vs. Animal Cells
Plant Cells

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Cell plate forms midway
between the two nuclei
of the cells.
The cell plate grows
outward until a new cell
wall has grown between
the two cells.
Animal Cells

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The cell membrane is
pulled in by a ring of
filaments.
This continues until the
cytoplasm is pinched in
two.
Breakdown of Mitotic Steps

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Prophase: Chromosomes coil up and become visible during
prophase. The nuclear envelope dissolves and the spindle
forms.
Metaphase: Chromosomes move to the center of the cell
and line up along the equator. Spindle fibers link the
chromatids of each chromosome to opposite poles.
Anaphase: Centromeres divide during anaphase. The two
centromeres (now called chromosomes) move toward
opposite poles as the spindles attached to them shorten.
Telophase: A nuclear membrane forms around the
chromosomes at each pole. Chromosomes, now at
opposite poles, uncoil and the spindle dissolves. The
spindle fibers break down and disappear.
Important Vocabulary
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Chromosomes:
– hold the cell’s DNA coiled up with proteins.
Chromatids:
– parts of chromosome that when paired with
its identical sister chromatid constitutes a
chromosome.
Centromere:
– The point where sister chromatids attach in
a chromosome.
Important Vocabulary
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Spindle:
– Cluster of microtubules that help separate
sister chromatids during mitosis.
Centriole:
– In animal cells it helps organize the
microtubules of the spindle.
Cytokinesis:
– Division of the cytoplasm during mitosis.