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Mitosis
Student Learning Objectives:
•
Distinguish between the different stages of Mitosis
Stages of Mitosis:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Introduction
In order for the body to grow and to repair damaged or old tissue cells, the cells must reproduce.
During the process of mitosis, cells identical to the original cell are created. This allows tissues
to produce more of the same kinds of cells to either increase the number of cells in the tissue or
to replace cells that have been lost from the tissue.
Interphase
When the cells are not actively dividing, they are in
a state known as interphase. During this stage the
cell is carrying out its daily activities: making
proteins and other materials, growing larger,
phagocytizing microbes – whatever the cell was
designed to do. The DNA of the cell, at this time, is
spread out in the form of chromatin, and the
individual chromosomes are not visible.
A
distinctive nuclear envelope (i.e. membrane)
surrounds the DNA, During mitosis, this cell will
split to form two cells.
Remember that the DNA holds the information for how the cell does its work. Each cell uses
only a small portion of the DNA to do its job. The differentiation (i.e. specialization of cells)
occurred because of the use of different areas of the DNA. Since the DNA plays such a critical
role in the life of the cell, each cell must have a complete copy of the DNA. Therefore, one of
the additional activities that will occur during interphase is the duplication, or replication, of the
DNA. The two copies of each chromosome will remain attached to one another until mitosis
occurs.
Mitosis
Mitosis is the process of active division in the cell. There are several stages to the mitosis
process: prophase, metaphase, anaphase, and telophase. During prophase, the DNA coils up
around special proteins to form the chromosomes. The nuclear envelope disappears and the
DNA is released into the cytoplasm. The centrioles duplicate and then move to opposite sides, or
poles, of the cell.
In metaphase, the chromosomes line up single-file at the center of the cell. Tiny fibers emerge
from the centrioles and connect onto the individual copies of DNA. These small fibers will help
to separate the copies of DNA that were created during DNA replication. Cells that lack
centrioles are unable to undergo mitosis. This would include neurons and certain kinds of
muscle cells.
Anaphase begins as the duplicate chromosome copies separate and begin to move towards the
poles of the cell – drawn by the fibers from the centrioles. This helps to provide each cell with
only a single copy of each strand of DNA.
As the chromosomes approach the poles of the cell, the cells begins to split into two separate
cells using a process known as cytokinesis. This splits the cytoplasm and organelles equally
between the two cells that are formed during mitosis. Cytokinesis occurs during the final stage
of mitosis known as telophase. As the cell proceeds through telophase, the chromosomes
uncoil, returning to the chromatin form, and the nuclear envelope reforms. The cells then return
to interphase and begin the process all over again. Some cells undergo mitosis regularly; others
undergo mitosis only occasionally, depending upon the type of tissue involved.