what causes cancer
cancers occur when the rate of cell multiplication is faster than the rate of cell death. this causes the growth of a tumor, often in tissues with a high rate of mitosis , such as the lung, bowel and bone marrow.
cancers are caused by damage to DNA. DNA can be easily damaged by physical factors such as UV light. it can also be damaged by chemicals, known as carginogens, which may be in the enviroment or can be produced by cell metabolism. mutations can also occur when cells divide, for example if DNA is copied incorrectly in gemete formation , an inherited form of cancer can result.
telling cells what to do
there are two types of genes that have a role in the control of the cell cycle and play a part in triggering cancer, these are:
- tumor supressor genes
oncogenes code for the proteins that stimulate the transition from one stage of the cell cycle to the next. mutations in these cells can lead to the cell cycle being continually active. which may cause excessive cell divison, resulting in a tumor.
tumor supressor genes produce supressor proteins that stop the cycle. so mutations inactivating these genes mean there is no break in the cycle.
gene defects have been identified that influence the development of cancer.
envirioment and cancer
the envrioment can either cause physical or chemical damage to an induvidual making cancer more likely.
smoking severly increases the risk of a person developing lung cancer through carcinogens in tar. this tar lodges in the bronchiand causes damage to DNA in surrounding epithelial cells.
UV light physically damages DNA cells in the skin. moles which have been affected by UV light may grow bigger and develop into a tumor. if the tumor is not removed the cancer cells can spread to other parts of the body.
diet is also linked to prevention and the development of cancer. A diet rich in antioxidants which destroy radicals cna help prevent cancer.