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GlossaryMain Menu
Cell Cycle
Interphase
Cytokinesis
Mitosis
What Is It? Why Do We Need It?
Cellular Structures Glossary
Mitosis Animation
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The Cell Cycle The Cell Cycle
The cell cycle is the sequence of growth and division of a cell. It consists of three major
phases: Interphase, mitosis, and cytokinesis. Cell division results in two cells that are both
identical to the parent cell.
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Why do cells grow and Why do cells grow and divide?divide?
All cells come from other cells. As organisms grow and change (a growing
vine, or a tadpole changing to a frog) new cells need to be produced. Cell growth and division also allows worn-
out tissues to be repaired and/or replaced.
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InterphaseInterphase
Interphase is the phase where the cell spends the majority of its life. During interphase, the cell grows,
carries on metabolism, and chromosomes are duplicated to form sister chromatids in order to prepare
for cellular division.
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MitosisMitosis
Mitosis is the phase where nuclear division takes place and the cell
divides. Mitosis occurs in a sequence of 4 stages: Prophase,
metaphase, anaphase, and telophase.
View Animation
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CytokinesisCytokinesis
Cytokinesis is the final phase of the cell cycle. This is where the
cytoplasm divides. In animals, the plasma membrane pinches along the equator of the cell. In plants, the cell plate is laid down across the equator and new cell walls form on each side.
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ProphaseProphaseProphase is the longest of the mitotic stages. During prophase, four major
cellular changes take place:• Chromatin coils to form visible
chromosomes.• The nucleus begins to disappear.• Centrioles migrate to opposite ends of the
cell.• Spindle fibers begin to form.
Mitosis
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MetaphaseMetaphase
Metaphase is a shorter mitotic stage. Several things occur during
metaphase…
Mitosis
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Metaphase…Metaphase…
First, chromosomes begin to move to the equator of the spindle.
Mitosis
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Metaphase…Metaphase…
Each sister chromatid attaches to a separate spindle fiber via its
centromere.
Mitosis
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Metaphase…Metaphase…
These spindle fibers extend from opposite poles. This ensures that each
new cell receives an identical and complete set of chromosomes.
Mitosis
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Metaphase…Metaphase…
When metaphase is complete, the spindle has formed completely and the sister chromatids are attached along the equator of the spindle.
Mitosis
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AnaphaseAnaphaseDuring anaphase, the centromeres split, and sister chromatids migrate
to opposite poles of the cell.
Mitosis
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TelophaseTelophaseTelophase is the final stage of mitosis.
The chromotids have now reached the poles of the cell and unwind into
chromosomes. This allows metabolic activity to recommence.
Mitosis
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Telophase…Telophase…Many of the processes that occurred
during prophase reverse themselves.
Mitosis
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Telophase…Telophase…• The spindle fibers break down
• The nucleolus reappears• The nuclear envelope forms
• Two nuclei now exist that are identical to the nucleus of the parent cell.
Mitosis
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GlossaryGlossary• centriole• centromere• chromatid• chromatin• chromosome• nuclear envelope• nucleolus• nucleus• spindle• spindle fiber
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centriolecentrioleA centriole is a barrel microtuble structure
found in most animals cells. Two centrioles arrange themselves
perpendicularly to form a centrosome. Centrioles organize the mitotic spindle upon which chromosomes are pulled
apart during cellular division.
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centromerecentromereThe centromere is a region of the
chromosome where the spindle fibers of the mitotic spindle attach. The
centromere is also the point of attachment of the two sister chromatids
once a chromosome has been duplicated for cellular division.
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chromatidchromatidA chromatid is one strand of the
chromosome after it has duplicated for cellular division. The two chromatids are called “sister chromatids” and will eventually split and move to opposite
ends of the cell.
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chromatinchromatin
Chromatin is the building block for a chromosome. It is only made visible by
staining. It consists of DNA and proteins. When the cell prepares to
divide, the chromatin thickens and can be seen as distinct chromosomes.
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chromosomechromosome
A chromosome is a long, continuous piece of DNA which contains the
genetic information for a cell.
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nuclear nuclear envelopeenvelope
The nuclear envelope is the double membrane of the nucleus in eukaryotic cells. It separates the contents of the
nucleus from the cytosol.
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nucleolusnucleolus
The nucleoulus is a “suborganelle” of the nucleus. It refers to a “knot” of
chromatin located within the nucleus. No membrane surrounds the nucleolus.
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nucleusnucleus A nucleus is found in all eukaryotic cells.
It is a structure that contains the cell’s genetic material. The nucleus controls chemical reactions that take place in the cytosol, regulates expression of
genes, and stores information needed for cellular division. The nucleus is
surrounded by a membrane called the nuclear envelope.
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spindlespindle
The mitotic spindle is a network of microtubules that is formed during the
prophase stage of mitosis.