Lauren Kenney
English 202C technical description
Mitosis
Mitosis is simply the duplication of all the parts of a cell, including its genetic
material (DNA). This process takes place inside the cells’ nucleus (control center).
During mitosis, replicated chromosomes (threads of DNA) divide creating two new
identical cells with the same composition and the same number of chromosomes.
These two new cells are called daughter cells. The movement of chromosomes is
directed by a structure called the mitotic spindle, which is part of the centrioles (sets
of tubes and proteins on each side of the cell). Threads that come out of the mitotic
spindle attach to each chromosome to align then before pulling them apart.
Two identical daughter cells come from one original cell. The original cell goes
through 5 basic steps in order to create these two daughter cells. These 5 steps (in
order) are Prophase, Metaphase, Anaphase, Telophase, Interphase. These steps can
easily be remembered as “PMATI”.
Prophase:
Prophase can be summed up as a preparation phase. This phase of mitosis
duplicates then separates the genetic material so that the cell can prepare to pass on
copies of its genetic material to the daughter cells.
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DNA Duplication
Once the cell is ready to duplicate, the DNA and proteins inside the cell nucleus
called chromatin condense. These strands of chromatin become so densely compact
that they begin to form chromatids (threads of DNA). While each chromatid is made
up of one single strand of DNA, one chromatid joins with another identical
chromatid (sister chromatid) at the centromere (center point) in an “X” shape to
make up a single chromosome. At this point, these chromosomes are visible under a
light microscope.
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Centriole Movement
After the chromatids are replicated and connect to form chromosomes, the
centrioles move to opposite poles (sides) of the cell. Another structure begins to
appear between the centrioles called a mitotic spindle. This is a group of threads
attached to the centrioles that aid with lining up the chromosomes, and separating
the sister chromatids into each new cell.
Metaphase:
Now that prophase has prepared the cell, metaphase is the step in the process that
lines up the duplicated genetic material (chromosomes) before it is time to be
separated.
The cell’s chromosomes form a protein wrap called kinetochore around the
centromere. The chromosomes then align themselves with the help of the mitotic
spindle, and then the threads that extend from the spindle on both sides of the cell
attach to the newly formed kinetochore. These threads then pull the each
chromosome back and forth until it lines up on an imaginary boundary through the
middle of the cell. This imaginary middle line is called the metaphase plate.
This is one of the most important steps to ensure that all of the chromosomes are
properly lined up and attached so that each cell only gets one copy of each when it is
time to separate.
Anaphase:
Anaphase is finally the step that separates the genetic material of the original cell
into two new identical daughter cells.
At this point in the process, all of the chromosomes are lined up along the
metaphase plate with threads from the mitotic spindle pulling them on opposite
sides. (Remember that each chromosome is made up of two sister chromatids). Each
chromosome is then separated simultaneously at its centromere into two identical
sister chromatids. These sister chromatids are pulled to the opposite pole of the cell
by the spindle threads so that each new daughter cell gets the same chromosomes.
Telophase:
Telophase is the final phase of mitosis. This is the part when the actually cell
division takes place. Telophase begins once the chromosomes are separated into
their sister chromatids, and each sister chromatid reaches the opposite side of the
cell. A membrane (boundary line) forms around each set of chromatids to separate
the two soon to be cells. The cell undergoes another process called cytokinesis that
actually divides the cell along the membrane. As this happens, each chromatid is
slowly uncoiling and becoming less compact to the point where it is no longer
visible under a light microscope. Each cell now has one copy of the DNA from the
original cell.
Interphase:
This phase is just the normal functioning phase of the cell. This can also be referred
to as the resting or idle state. The cell is in interphase before it is time to start the
process over.
Summary
Mitosis is a process of division of the nucleus of a cell that occurs when a cell divides
to produce two identical daughter cells. The main focus of this process is evenly
separating the genetic material from the parent cell. The process of mitosis is
commonly broken down into 5 steps, “PMATi”, known as prophase, metaphase,
anaphase, telophase, and interphase. Mitosis is important because it helps normal
development and it also a component of cancer.
Images/References
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http://www.accessexcellence.org/RC/VL/GG/mitosis.php
http://cyberbridge.mcb.harvard.edu/mitosis_5.html
http://www.rememberg.com/Special-numbers/mitosis-phases--Mnemonicto-remember-the-phases-of-Mitosis