Dana Ellsbury
ENGL 202C
Mitosis: The Eukaryotic Cell Replication Process
Animalia Mitosis
Introduction
The process of mitosis is an important aspect of your ability to live. Ever wonder how our
bodies can be damaged and still survive? How does your body fix itself after being sick or
getting your skin cut? Mitosis is the process in the cell cycle in which a cell replicates itself
creating two identical daughter cells. The steps involved in mitosis are:





Prophase
Prometapase
Metaphase
Anaphase
Telophase
The five step process, followed by cytokenesis, is required for growth and development, repair
and replacement of damaged parts, and asexual reproduction of a eukaryotic organism.
While eukaryotes require mitosis for survival in many ways, prokaryotic organisms lack a
nucleus and nuclear envelope within their cells so they divide via binary fission. Eukaryotic
organisms include kingdoms:




Animalia
Fungi
Plantae
Chromalveolata
Though all eukaryotic organisms use mitosis for survival, they use them in different ways
depending on their cell types and contents. This document will focus on the process of mitosis
in the kingdom Animalia. The purpose of this document is to inform students about mitosis in
Animalia organisms who have the intent to gain a science degree.
Contents of the Animalia Cell Needed for Mitosis
There are three main components of the Animalian nucleus. The
nucleolus is a structure found in the center of the nucleus
containing ribonucleic acids and proteins to help the function of
the cell as a whole. The nucleus is the surrounding material of
the nucleolus comprised of chromatin tightly wrapped by
chromosomes containing the DNA of the organism. The nucleus is contained
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Dana Ellsbury
ENGL 202C
within a shell-like membrane called the nuclear membrane that protects the DNA from being
damaged by any invading structures that may penetrate the whole cell membrane (represented
as tan in the figure to the right).
Interphase: Cell Preparing for Mitosis
Interphase precedes mitosis in the cell cycle. This process is divided into three phases: G1, S,
and G2. Interphase helps the cell to grow and prepare for mitosis. There are checkpoints
throughout the cell cycle to allow or stop a cell from moving forward in the process. These
checkpoints help to ensure the cell is ready for the beginning phases and is divided correctly in
mitosis.
The G1 phase allows the cell to grow in size before moving to S phase where the cell continues
to grow while it duplicates its chromosomes in the nucleus. G1 phase is important as growth of
the cell for S phase to occur and have substantial amount of space for double the chromosomes
within the cell. When a cell finishes the S phase, the cell continues to grow in G2 phase with
sister chromatids (two of the same chromosome) produced from the previous phase. The
continual growth in G2 is required for the splitting of the cell in the final phase of mitosis. At the
end of the G2 phase, a checkpoint is present to monitor if the cell grew enough before entering
the first phase of mitosis.
Phases of Mitosis and their Processes
Prophase
When a cell completes interphase and passes the checkpoint, the chromatins in the nucleus
begin to condense down to chromosomes and the nuclear membrane encasing them begins to
dissolve. Under normal conditions, the chromosomes are loosely coiled around chromatins but
the checkpoint at the end of G2 is a signal to the cell that allows chromatin fibers to coil tightly
creating condensed chromosomes. This phase is typically visible through high magnification of
light microscopy. Centrosomes reside in close proximity of the cell nucleus.
Prometaphase
After the chromosomes are condensed, the nuclear membrane is
completely broken down; the microtubules of the centrosomes
begin to invade the nuclear space. Each chromosome forms two
kinetochores at its centromere, one attaching to each sister
chromatid. Kinetochores are similarly a ring structure to allow
attachment to microtubules. The spindles of the centrosomes
lengthen and the microtubules attach to kinetochores while non2
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Dana Ellsbury
ENGL 202C
kinetochore microtubules attach to opposing non-kinetochores forming a mitotic spindle. These
kinetochores are also called polar microtubules due to their polar characteristics in metaphase
and anaphase.
Metaphase
The centrosomes form opposite poles within the cell and begin to pull on the chromosome
centromeres to create tension with the two ends of the cell; the polar microtubules push
against each other pushing the centrosomes to opposing sides. The centromeres on the
chromosomes create an equatorial plane resembling a line in the center of the cell; this is called
the spindle equator caused by counterbalancing of pull from the kinetochores on the
chromosomes. Every kinetochore must be attached to a microtubule for the next phase to
occur; there are suggestions that the unattached kinetochores create a signal to prevent
anaphase to occur.
Anaphase
When all of the kinetochores have attached microtubules and the
spindle equator is created, the protein connecting the sister
chromatids at the centromere is cleaved off creating two daughter
chromosomes. The centrosomes of opposite ends begin to shorten
their spindle fibers separate the sister chromatids at their
centromere.
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Elongation of the polar microtubules, shorten the kinetochore microtubules and pull
the
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In the final phase of mitosis the polar microtubules continue to lengthen which elongates
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cell. A new nuclear membrane is formed around the daughter chromosomes located at polar
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membrane of the parent cell. The nucleolus reappears and both sets of chromosomes
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relax back into loosely coiled chromatin. Mitosis is complete and the cell can now divide
through cytokinesis.
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Dana Ellsbury
ENGL 202C
Cytokinesis
This stage is often confused with being the final part of telophase, though it is a completely
different process that begins at the same time as telophase. In this process, a cleavage furrow
(pinch) containing a ring develops where the metaphase plate was established in the parent
cell. This is achieved by Myosin II and actin filaments that create a contractile ring, splitting the
parent cell into two daughter cells containing equal amounts of chromosomes contained in
their newly formed nucleus membrane.
Conclusion
Mitosis is important for the maintenance of the chromosomal set containing an organisms
DNA; this process requires the same chromosomal composition of daughter cells from parent
cells for the process to be successful. Mitosis will occur with the development and growth of an
organism such as a growing embryo from a single zygote, the replacement of cells such as
healing a cut on the surface of the skin or burnt taste buds on the tongue, the regeneration of
body parts which is seen in sea stars regaining a lost limb, and asexual reproduction of
organisms called budding. Each phase of this process must be done correctly for the final
outcome to be successful with useable daughter cells. Without this process, many species
including humans would cease to exist.
References:
De Souza CP, Osmani SA. (2007). “Mitosis, Not Just Open or Closed”. Eukaryotic Cell 6 (9): 1521–7.
Doi:10.1128/EC.00178-07. PMC 2043359. PMID 17660363.
Maton A, Hopkins JJ, LaHart S, Quon Warner D, Wright M, Jill D. (1997). Cells: Building Blocks of Life. New Jersey:
Prentice Hall. pp. 70–4. ISBN 0-13-423476-6.
Raven PH, Evert RF, Eichhorn SE. (2005). Biology of Plants (7th ed.). New York: W.H. Freeman and Company
Publishers. ISBN 0-7167-1007-2.
Picture References:
http://www.proprofs.com/flashcards/story.php?title=intro-human-biology-107
http://www.mcatzone.com/glosslet.php?letter=c&pagenum=2
http://www.biology.iupui.edu/biocourses/N100H/ch8mitosis.html
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