Continuity of Life: Processes
Biology (Year 12)
What is mitosis?
Image: Mitosis cells sequence image, Image by LadyofHats, Sourced Under a Creative Commons 4.0 License from Wiki Commons
For many students, mitosis is one of those topics you've done to death. However, it is essential to know for your exam, as it could come up in an extended response or as a short answer question. Mitosis is what takes place in the 'M' phase of the cell cycle, where cell division of somatic cells occurs. Cells in the body undergo mitotic divisions for two primary purposes; growth and repair. The result of mitosis is two genetically identical daughter cells, which will go on to perform mitosis over and over again. There are four phases of mitosis. 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase
These can be remembered as 'PMAT' or 'IPMAT' if you include interphase (which isn't a part of mitosis!). Prophase
In prophase, chromatin threads in the nucleus condense and coil up tightly to become chromosomes, which are two sister chromatids held together by a centromere.
The nuclear membrane disintegrates, and the nucleolus disappears.
Mitotic spindle forms from the centrioles and spindle fibres attach to each chromosome at its centromere.
Two centrosomes that contain two centrioles move to opposite poles of the cell.
In metaphase, chromosomes move to the centre of the cell and line up on the cell's equator (note: the equator may also be called the metaphase plate).
The centromeres of the chromosomes are aligned together on the equator.
The centrioles are located at opposite poles of the cell.
During anaphase, the spindle fibres shorten and pull on the centromeres.
The chromosomes separate into sister chromatids and are pulled to opposite poles.
At the end of anaphase, each pole has an identical set of maternal and paternal chromosomes as DNA replication occurred during interphase.
In the last stage of mitosis (telophase), chromosomes decondense (uncoil) to form chromatin.
Two new nuclear membranes form, one for each new daughter cell.
The nucleoli reappear, and the spindle apparatus disappears.
The cell elongates, and a cleavage furrow (the dip between the (almost) 2 new cells) to become ready for cytokinesis.
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