Mitosis

Click here or press play below to see concise and engaging video tutorials from SnapRevise!

SnapRevise

This is a legacy topic. View the most up to date content by clicking an exam board tab above or visiting the home page.

Multi-cellular organisms such as ourselves are... multi-cellular. This point must be emphasised in learning about mitosis because mitosis is the process by which this is possible. A bacterium is a cell which divides to produce 2 bacteria, yet that cell is the organism itself. Multi-cellular organisms require a process by which one cell divides into two, those two into four, and so forth, until a gargantuan number of cells come alive. Cells are organised in tissues (such as skeletal muscle), tissues are organised in organs (such as the skin), and organs are organised into systems (such as the nervous system). The various systems make up the live organism.

Click here or the image below to download free resources from alevelbiology.co.uk!

Click to download!

Overview of Mitosis

Mitosis is the process by which cells divide to achieve growth and repair by simply increasing cell number. The dividing cell is called the parent cell, and the resulting two cells are called daughter cells (just a little bit sexist - sorry guys). The daughter cells are genetically identical i.e. clones, as they contain copies of the parent cell's DNA.


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 daughter 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 daughter cells.


Comments