Cell cycle
The squence of events which a cell experiences in cell division is called the cell cycle. The cell cycle occurs in three stages: a) Interphase, b) Mitosis and c) Cell divion
Interphase is where a cell synthesis materials needed in cell division. DNA replication occurs here. Mitosis is the process of nuclear division which occurs in 4 stages. Finally cell division, is the process of division of the cytoplasm in to two daughter cells.
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Mitosis
Mitosis occurs in 4 stages which are: prophase, metaphase, anaphase, telophase.Before all these 4 stages start, interphase must have allready finished. In interphase DNA has replicated, and chromatids join together to form a chromosomes. During interphase chromosomes material is in the form of very loosely coiled thread called chromatin. Centrioles have replicated. |
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Prophase
This is the first process in mitosis and it is usually the longest. Chromosomes shorten. Each chromosome consist of 2 chromatids. These chromatids are held together by a centromere. Centrioles which are small organells that form spindle fibers move to opposite poles of the cell. The nuclear envelope is no longer visible.
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Metaphase:
Chromosomes line up between the two centrioles found in opposite poles of the cell. Spindel fibers attach to the centromeres of the chromosomes, which are microtubes. |
Anaphase:
This stage is very rapid. The centrometers split into 2 and spindle fibres pull the daughter centromeres to opposite poles. The separated chromatids are pulled along behind the centromeres. |
Telophase
The chromatids reach the poles and then uncoils and lengthen to form chromatin again, losing the ability to be seen clearly. The spindle fibres desentigrate and the centrioles replicate. Nuclear envelope reappears. |
Cytocinesis
When a cell finally separates in to 2 new cells, this stage is called cytocinesis |
this picture shows a layer of onion in which you can see how cells are in constant division. |
