Cyclins are proteins involved in the control of the cell cycle.

Their changing levels start, control and end the events of the cycle.

https://en.wikipedia.org/wiki/Cyclin

Chromosomes

Figure 2.5.1 http://upload.wikimedia.org/wikipedia/commons/4/4b/Chromatin_Structures.png

Figure 2.5.2 http://en.wikipedia.org/wiki/Chromosome

Diagram of a duplicated and condensed Chromosome. It becomes this form ready for metaphase.This is so it can be easily moved to opposite poles of the cell.

The microtubule attach to the centromere (2)

The chromosome is made up of two

identical chromatids called sister chromatids.

These will be seperated during the anaphase stage of mitosis. The right one labelled (1) will be taken to one end of the cell and the left side

Notice the chromatid has a

Short arm.(3) and Long arm (4) .

Prophase

At the start of prophase DNA starts condensing and super cooling until there are distinctly visible chromosomes.

The chromosomes begin to condense and supercool

The nuclear membrane starts to breakdown

Metaphase attachment of spindle microtubules to centromeres

Anaphase

splitting of centromeres movement of sister chromosomes to

Telophase

Cytokinesis

this happens directly after mitosis is finished. It is where the two new cells completely separate. They then both start their own separate Interphases.

Tumour Formation

Sometimes mistakes can happen in the cell cycle and this can lead to the uncontrolled production of tumour cells. These mistakes are often caused by the action of substances called mutagens which can cause mutations in genes. This is especially important if these are genes that control the production of cyclins. Mutagens can also activate genes, so called oncogenes that can potentially lead to cancer. These factors can interfere in the complex biochemistry which controls cell division. Metastasis is the development secondary of tumours which can then spread tumour formation and thus cancer to other cells and tissues. This can happen to all of the different tissues of an organism

https://en.wikipedia.org/wiki/Oncogene#/media/File:Oncogenes_illustration.jpg