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The Cell Cycle & Mitosis Tutorial
What is (and is not) mitosis?
Interphase & mitosis
|Mitosis is nuclear division plus cytokinesis, and produces two identical
daughter cells during prophase, prometaphase, metaphase, anaphase, and
telophase. Interphase is often included in discussions of mitosis, but
interphase is technically not part of mitosis, but rather encompasses stages
G1, S, and G2 of the cell cycle.
||The cell is engaged in metabolic activity and performing its prepare
for mitosis (the next four phases that lead up to and include nuclear division).
Chromosomes are not clearly discerned in the nucleus, although a dark spot
called the nucleolus may be visible. The cell may contain a pair of centrioles
(or microtubule organizing centers in plants) both of which are organizational
sites for microtubules.
||Chromatin in the nucleus begins to condense and becomes visible in
the light microscope as chromosomes. The nucleolus disappears. Centrioles
begin moving to opposite ends of the cell and fibers extend from the centromeres.
Some fibers cross the cell to form the mitotic spindle.
||The nuclear membrane dissolves, marking the beginning of prometaphase.
Proteins attach to the centromeres creating the kinetochores. Microtubules
attach at the kinetochores and the chromosomes begin moving.
||Spindle fibers align the chromosomes along the middle of the cell nucleus.
This line is referred to as the metaphase plate. This organization helps
to ensure that in the next phase, when the chromosomes are separated, each
new nucleus will receive one copy of each chromosome.
||The paired chromosomes separate at the kinetochores and move to opposite
sides of the cell. Motion results from a combination of kinetochore movement
along the spindle microtubules and through the physical interaction of
||Chromatids arrive at opposite poles of cell, and new membranes form
around the daughter nuclei. The chromosomes disperse and are no longer
visible under the light microscope. The spindle fibers disperse, and cytokinesis
or the partitioning of the cell may also begin during this stage.
||In animal cells, cytokinesis results when a fiber ring composed of
a protein called actin around the center of the cell contracts pinching
the cell into two daughter cells, each with one nucleus. In plant cells,
the rigid wall requires that a cell plate be synthesized between the two
The University of Arizona
Thursday, April 24, 1997
the Development Team
All contents copyright © 1997. All rights reserved.
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