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Mitosis

The cytoskeleton

Cell division requires the active remodelling of the cell's cytoskeleton. The cytoskeleton is made of multiple kinds of protein that offer it the right structure and aid during the process of division.

The centriole is a tubey spaghetti thing that aids in cell division when the duplicated chromosomes need to move into their subsequent new offspring cells from the parent cell (during mitosis).




They're made of a special protein called tubulin because they're tubeeeeeeeeeeeees. Why didn't they call it spaghettulin? I guess spaghetti aren't hollow but...

Microtubules also play a key part in how cell organelles are moved and placed within the cell. Two associated centrioles form the centrosome. The microtubules are also where spindle fibres extend from when they separate chromosomes during cell division.


Stages of Mitosis

Prophase, metaphase, anaphase, telophase and cytokinesis.



There's no easy way around these stages, so just bloody learn them. Actually there is an easy way. Awesome video time!



Prophase

1. Chromosomes begin to appear visible under a microscope due to chromatin (the coiled and yet-again coiled DNA fibre) condensing. Before this the DNA is not specifically distinguishable in the shape of chromosomes. This is a terrible word tangle so this is how it is. From a bowl of spaghetti (the nucleus) put the spaghetti in the shape of several chromosomes. Chromatin is the spaghetti initially, and chromosomes are the spaghetti still, just turned and twisted and distinguishable as individual stick-shaped objects. That is all, that's all it is. Before this happens though, the DNA must be replicated - that's the reason behind the X shape of chromosomes; they are two "lines" a.k.a. chromatids joined together at their centres called centromeres.

2. The nuclear envelope breaks down.

3. Organelles known as centrioles migrate towards the poles of the cell. These organelles are involved in the act of pulling the chromosomes apart into the soon-to-be offspring cells. They achieve this by the microtubules that extend out of them and connect to the centromeres. Microtubules are like lassos. Sort of.




Metaphase

1. Chromosomes are aligned at the cell equator by spindle fibres (made of the aforementioned microtubules) which lengthen and shorten themselves on opposing sides (tug of war) until all chromosomes are lined up about halfway across the cell. This area is called the metaphase plate. It looks like a plate. Who said biology can't be straightforward?




Anaphase

1. The chromatids split at their centromeres and are pulled towards opposite poles of the cell by the shortening spindle fibres.




Telophase

1. Nuclear envelopes reform around the two new nuclei.

2. The chromosomes decondense and become indistinguishable under a microscope yet again, and the spindle fibres spread out.




Cytokinesis

This is the final step of mitosis when the cytoplasm of the parent cell divides to complete the cell division, resulting in two brand new and individual offspring cells.




Anticancer drugs that target mitosis in an attempt to stall the fast-diving cancer cells include vincristine and 5'Fluorouracil. Vincristine acts as a microtubule formation inhibitor a.k.a. mitosis poison. Without microtubules to orchestrate the division of the chromosomes into two new cells, division ceases.

5'Fluorouracil acts as an antimetabolite by interefering with DNA synthesis in S phase. This prevents the cell going into mitosis, or indeed being functional as it doesn't have the DNA it needs.

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