Biology 6.2 Mitosis and Cytokinesis
Mitosis and
Cytokinesis
Objectives
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Students will. . . .
 Describe the structure and function of the spindle during
mitosis
 Summarize the events of the four stages of mitosis
 Differentiate cytokinesis in animal and plant cells
Chromatid Separation in Mitosis
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Every second about 2 million new
blood cells are produced in your
body by cell divisions occurring
in the bone marrow.
These cells have received the
signal to divide.
The cells advance beyond the G2
phase and enter into the last
two phases; mitosis and
cytokinesis.
Chromatid Separation in Mitosis
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During mitosis, the nuclei
divide to form two nuclei,
each containing a complete
set of the cell’s
chromosomes.
Chromatid Separation in Mitosis
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During mitosis, the
chromatids on each
chromosome are physically
moved to opposite sides of
the dividing cell with the
help of the spindle.
Spindles are cell
structures made up of
both centrioles and
individual microtubule
fibers that are involved in
moving chromosomes
during cell division.
Forming the Spindle
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At each of the cell’s poles lies a
centrosome.
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The centrosome is an organelle that
organizes the assembly of the spindle.
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In animal cells, a pair of centrioles are
found inside each centrosome.
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Centrioles and spindle fibers are both
made of hollow tubes of protein called
microtubules.
Each spindle fiber is made of an
individual microtubule.
Each centriole however, is made of nine
triplets of microtubules arranged in a
circle.
Mitosis and Cytokinesis
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Although mitosis is a
continuous process, biologists
traditionally divide it into four
stages
 Step 1: Prophase
 Step 2: Metaphase
 Step 3: Anaphase
 Step 4: Telophase
Mitosis and Cytokinesis
Step 1: Prophase
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Chromosomes coil up
and become visible
during prophase.
The nuclear envelope
dissolves and a spindle
forms.
Mitosis and Cytokinesis
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Step 2: Metaphase
During metaphase, the
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.
Mitosis and Cytokinesis
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Step 3: Anaphase
Centromeres divide
during anaphase.
The two chromatids
(now called
chromosomes) move
toward opposite poles
as the spindle fibers
attached to them
shorten.
Mitosis and Cytokinesis
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Step 4: Telophase
A nuclear envelope forms
around the chromosomes
at each pole.
Chromosomes, now at
opposite poles, uncoil and
the spindle dissolves.
The spindle fibers break
down and disappear.
Mitosis is complete.
Cytokinesis
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As mitosis ends with the
cell nucleus being divided,
cytokinesis begins.
During cytokinesis, the
cytoplasm of the cell is
divided in half, and the cell
membrane grows to enclose
each cell, forming two
separate cells as a result.
The end result of mitosis
and cytokinesis is two
genetically identical cells
where only one cell existed
before.
Cytokinesis: the cytoplasm divides
Cytokinesis
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In plant cells and
other cells that have
rigid cell walls, the
cytoplasm is divided in
a different way.
Cell plate
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In plant cells, vesicles
formed by the Golgi
Apperatus fuse at the
midline of the dividing
cell and form a cell
plate.
Cytokinesis
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A cell plate is a
membrane bound cell wall
that forms across the
middle of the plant cell.
A new cell wall than
forms on both sides of
the cell plate.
When complete, the cell
plate separates the plant
cell into two new plant
cells.
Cell plate
Key Concepts. . . .
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During mitosis, spindle fibers drag the chromatids
to opposite poles of the cell.
A nuclear envelope forms.
Each resulting nucleus contains a copy of the
original cell’s chromosomes
Cytokinesis in animal cells occurs when a belt of protein
threads pinches the cell membrane in half.
Cytokinesis in plant cells occurs when vesicles from the Golgi
Apparatus fuse to form a cell plate.
Computer Lab
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Go to the computer lab.
Today’s assignment is to research the “Cell Cycle”,
including mitosis and cytokinesis, and sequence the steps
in order demonstrating the order of cell division.
Create a written 1 page with all the steps in order with a
brief explanation of each step.
Match this one written page to a diagram you have
located online or created yourself demonstrating the
complete cycle.