There are many different types of cancer and there can be a number of different causes for each one. However, researchers think that cancers happen when the normal control of cell division goes wrong. This can be triggered by a mutation in the genes of a single cell.
A mutation is simply a change in the structure of the cell's DNA. Everybody has DNA that contains mutations and these mostly do not cause any problems because they are not part of the cell's genes. However, if the mutation happens in a gene, it can cause disorders such as cystic fibrosis or haemophilia. The mutation is copied during cell division and can be passed to future generations during reproduction. These types of mutations lead to inherited disorders such as cystic fibrosis and haemophilia.
Roll over Picture 12 to see how small the difference
can be between a normal gene and one that carries a mutation.
Larger mutations can happen when sections of chromosomes
become reversed or even moved and attached to another chromosome.
Gene mutations and cancers
Mutations can be very small changes. The information in DNA is carried in the sequence of bases. Changes in just one or two bases can scramble the information and mean that the gene does not work properly. If this mutation is in a gene that controls cell division it can trigger the uncontrolled growth of that cell. This faulty gene is copied to all the new cells and so the uncontrolled growth continues and the new cells form a tumour.
Click on the animations to see the effects of a mutation on cell growth.
Picture 13. Normal cells stop growing when they have replaced any damage or come into close contact with other cells. This helps to regulate their growth. Open the animation in a new window.
Picture 14. Cancer cells do not stop growing when they are in close contact with other cells. This means they can form a tumour that can spread into other tissues. Open the animation in a new window.
Picture 15. See question 6. This is a cell of an imaginary animal. A human cell contains 23 pairs of chromosomes.
