Mitosis Close Up


Before mitosis begins, cells are in the interphase stage, which is the rest period between mitotic divisions.   At this time, the chromosomes are not identifiable but are an undifferentiated loose mass of stretched out DNA molecules within the nucleus.  Chromosome replication and other cell processes are occurring in preparation for mitosis.  In addition, cells carry out normal metabolic activities at this time.  Most mammal somatic cells, including those of humans, spend at least 90% of their time in interphase.

drawing of interphase stage of mitosis--there is an undifferentiated chromosome mass in the nucleus


Interphase

At the beginning of the first mitotic stage, prophase, the thread-like doubled chromosomes contract and become visible.  The two centrioles move to opposite sides of the nucleus.  At the same time, the nuclear membrane begins to break down.

drawing of prophase stage of mitosis--doubled chromosomes contract and become visible; two centrioles move to opposite sides of the nucleus; and the nuclear membrane begins to break down


Prophase     

During metaphase, the nuclear membrane disappears and the chromosomes become aligned half way between the centrioles.  The centromere of each doubled chromosome becomes attached by thread-like spindle fibers to the centrioles which are at polar opposite sides of the cell.

drawing of metaphase stage of mitosis--the nuclear membrane disappears and the chromosomes become aligned half way between the centrioles; the centromere of each chromosome becomes attached by thread-like spindle fibers to the centrioles which are at polar opposite sides of the cell


Metaphase 

During the following anaphase stage, the chromatids of each chromosome separate at their centromeres and then migrate to the opposite poles of the cell.

drawing of anaphase stage of mitosis--the chromatids of each chromosome separate at their centromeres and then migrate to the opposite poles of the cell


Anaphase

During telophase, two distinct nuclear membranes develop encompassing the two identical sets of chromosomes.  At the same time, the cytoplasm divides between the two new cells, and the cell membrane begins to pinch off the cell contents into two daughter cells.

drawing of telophase stage of mitosis--two distinct nuclear membranes develop encompassing the two identical sets of chromosomes; the cytoplasm divides between the two new cells and the cell membrane begins to pinch off the cell contents into two daughter cells


Telophase

Finally, the new identical cells separate and once again enter interphase in preparation for a later mitotic division.  While the chromosomes are no longer visible, they will be replicated just before mitosis begins.

drawing of the return to interphase stage after mitosis is complete--new identical cells separate and again enter interphase


Interphase

 

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Copyright 1997-2012 by Dennis O'Neil. All rights reserved.
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