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Asked by anon-254980 on 18 May 2020.
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Chris Watt answered on 18 May 2020:
Within every cell, there is a nucleus which contains the DNA. The DNA is made up of genes which are sets of instructions for making different proteins. Some of these proteins are important for telling the cell when to grow, when to divide and when to die. The cell also receives messages from other cells. During the cell cycle, there are proteins that make sure the cell has grown to the right size and also to make sure it is now ready to divide (like a checkpoint). There are hundreds of different cell types (such as skin cells, heart cells, hair cells) which need to grow to different shapes and sizes; different cells produce different types and amounts of these proteins and this is how they are able to grow to the size and shape they need to be and do the job they need to do within the body. This is a very tightly controlled process and is very efficient. However, very rarely, a fault within a gene may cause a cell to produce faulty proteins which may result in cells dividing more than they should, or to start ignoring messages telling the cell to die. This is how tumours and cancer can form.
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Judith Sleeman answered on 19 May 2020:
In the body, a lot of cells are no longer able to divide (like many brain cells) but some cells (in skin and in the gut for example) divide rapidly to replace themselves. So, the decision of when to divide is a mixture of whether new cells are needed and whether the cell is at the correct size to make 2 new ones. There are a large number of proteins involved in deciding when a cell should divide (also called controlling the cell cycle) and the balance of the amounts and activities of these proteins are what makes the ‘decision’. A lot of the genes (bits of DNA) that carry the instruction to make these proteins were discovered in yeast by looking at faulty yeast that divided too soon and ended up getting really small.
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