Question: what causes cells to mutate? why do they reproduce when theyre not meant to?

Ken Dutton-Regester answered on 16 Mar 2012:

There is a bunch of reasons why cells can mutate- or more specifically, why their DNA gets mutated. In regards to melanoma or skin cancer, the biggest culprit is the sun. The sun produces UV radiation which can mutate our DNA. This is an example of a carcinogen. In regards to other cancers- lung cancer is caused by cigarettes or smoking. What you might not know is that mutations occur in our DNA all the time. This is because the cellular machinery that replicates or makes copies of our DNA (when a cell divides) are not perfect and can make a mistake. Luckily there are other mechanisms or proteins in the cell that fix the majority of these errors or mutations. However, some mutations may not be fixed and the ones that occur in important regions of genes are responsible for cancer. When a mutation occurs in our DNA, it can change the shape of a protein (the product of a gene) which can than affect the protein activity in a variety of ways. When mutations occus in proteins that are responsible for cell division, that can cause the cells to divide uncontrollably and cause cancer.