Download MITOSIS Introduction Objectives: The first objective is to appreciate

MITOSIS
Introduction
Objectives: The first objective is to appreciate the importance and the role that
definitions have in technical writing. The second is to understand how audience and
purpose indicate the need for definition. The third is to be able to differentiate between
the levels of details in definition. The last is to be able to select the right level of detail
according to the situation.
Criteria: The first criterion for this assignment directed us to choose a relatively complex
term, and choose an audience of “non-technical readers” to explain the term to. The
second criterion was to compose a parenthetical and sentence definition for the term.
The last criterion was to compose an expanded definition using multiple expansion
strategies, including at least one visual and at least 3 references.
Parenthetical Definition
Mitosis (cell division) is a major part of the cell cycle.
Sentence Definition
Mitosis, a form of cell division, is a part of the cell cycle where the DNA in one cell is
duplicated and two new daughter cells are formed each with identical DNA.
Expanded Definition
How was mitosis discovered?
Mitosis was first discovered in cat, rabbit, and frog cornea (eye) cells in 1873. It was
described for the first time by the Polish histologist Waclaw Mayzel in 1875. Walther
Flemming coined the term “mitosis” in 1882 (Sharp, 1934).
What is the significance of mitosis?
Mitosis is important in maintaining the DNA; every cell receives identical DNA from the
mother cell, and continues it to pass it onto the following generation of cells. Mitosis is
essential in the development and growth of an organism. The more mitosis that occurs,
the more the organism can grow and develop. Also, in certain parts of the body like
inside the mouth or the skin, cells are constantly being destroyed. Because of mitosis,
exact copies of those cells can quickly be created to maintain those parts of the body.
Mitosis is very important to organisms that can regenerate limbs. An example of this can
be seen in Starfish: they can regenerate lost limbs via mitosis. Single celled organisms
that reproduce via asexual reproduction do so via mitosis.
What are the five phases of mitosis?
The first phase is interphase. In this phase, the cell grows, duplicates its proteins and
nucleic acids (building blocks of DNA), and creates new organelles (Blow & Tanaka,
2005).
The next phase is prophase; the cell prepares to divide. The DNA is duplicated and then
tightly packaged. Structures called centromeres are created that can connect to the
DNA, and assist in the separation of the DNA to prepare for cell division (Blow & Tanaka,
2005).
The third phase is metaphase. The centromeres send out mini-structures that attach to
the condensed DNA. After attachment, the centromeres begin pulling the DNA towards
opposite ends of the cell. This ensures that there will be an equal distribution of DNA
into the new future daughter cells (Winey et al., 1995).
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In the second last phase, anaphase, the two identical DNA reach their most condensed
state. They are pulled to opposite ends of the cell and separation begins (Winey et al.,
1995).
The final phase consists of telophase and cytokinesis. Here, the separation of DNA
forces the singe cell to elongate. Eventually, the cell membrane enclosing the single cell
closes in, pinches, and splits the cell into two identical daughter cells. Each of these cells
will grow until each is ready for mitosis again (Winey et al., 1995).
Figure 1: Picture showing telophase and cytokinesis stage of mitosis (Sharp, 1934).
Figure 2: Diagram showing the different phases of mitosis (Reece & Urry, 2011).
What are possible errors and variations of mitosis?
An error that can occur during the embryonic development stage in humans can result
in a cell that has too few or too many chromosomes (tightly coiled DNA wrapped around
proteins). This error is a condition that is often associated with cancer (Draviam et al.,
2004). If the DNA fails to completely separate onto opposite ends of the cell, the result
is nondisjunction: one cell has too much DNA and the other has none (Iourov et al.,
2006). This is an error that occurs during anaphase.
References:
Blow, J. J., & Tanaka, T. U. (2005). The chromosome cycle: coordinating replication
and segregation. EMBO reports, 6(11), 1028-1034.
Draviam, V. M., Xie, S., & Sorger, P. K. (2004). Chromosome segregation and genomic
stability. Current opinion in genetics & development, 14(2), 120-125.
Iourov, I. Y., Vorsanova, S. G., & Yurov, Y. B. (2006). Chromosomal variation in
mammalian neuronal cells: known facts and attractive hypotheses.
International review of cytology, 249, 143-191.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B.
(2011). Campbell biology (p. 379). Boston: Pearson.
Sharp, L. W. (1934). Introduction to Cytology. New York City, NY: McGraw Hill.
Winey, M., Mamay, C. L., O'toole, E. T., Mastronarde, D. N., Giddings, T. H., McDonald,
K. L., & McIntosh, J. R. (1995). Three-dimensional ultrastructural analysis of
1601-1615.