The Link Between Cancer and Mitosis

The Link Between Cancer and Mitosis
Cancer is one of the most common diseases in the developed countries, accounting for around one in four deaths. In Britain it caused about 25% of the deaths h in 1991 and is the most common cause of death following cardiovascular disease. There are, in fact, over 200 different forms of cancer, which is why it is not necessarily thought of as a single disease. For example, breast cancer is the most common form in women and lung cancer in men. Cancers are a result of uncontrolled mitotic cell division, which is the division of one cell to produce two genetically identical daughter cells. The problem is cased by mutations or abnormal activation of the genes which control cell division. We can say that a gene has been mutated if there is a change in one of the bases; for example, one base turns (e.g. adenine) into another base (e.g. thymine). This can lead to uncontrolled cell division. When genes are abnormal (or have been mutated) they are called oncogenes (onkos means tumour), about a hundred of which have been discovered.
Cancerous cells will divide uncontrollably and repeatedly forming clones of genetically identical cells. Therefore, thought the mutation may start off in only one cell, it can be passed on to the cells decedents, so the daughter cells will too have the mutated gene. Eventually an irregular mass of relatively undifferentiated cells called a tumour is formed. By the time a tumour is detected it may contain about a thousand, million cells, which show abnormal changes in shape. There are basically two different types of tumours- malignant and benign. Tumour that spread and eventually cause ill health and death are described as malignant. However, the majority of tumours, such as common warts, do not spread and are described as benign. Tumour cells can break away and spread to other parts of the body, particularly in the bloodstream and lymphatic system, causing secondary tumours or metastases. This process is called metastasis. The spread of cancers in this way is probably one of the most dangerous aspects of cancer, as it can be very difficult to find these secondary tumours and remove them. Changes in genes are called mutation and any factor that brings about one is called a mutagen. An agent that causes cancer is called a carcinogen. Most mutated cells either destroyed by the bodies immune system or die with no ill effect on the body. Some of the factors that increase mutation rates, and therefore the likelihood of cancer, include chemicals, viruses, and ionising radiation. Cancers have also been known to have hereditary links. Ionising radiation includes X-rays, gammer rays and particles from the decay of radioactive material. They cause the formation of damaging ions inside cells that can break dna strands. With the depletion of the ozone layer, increasing amounts of ultra- violet light, which can damage genes, are getting to the earths surface causing increased cases of skin cancer. Many different chemicals, which have been shown to damage dna molecules, have been shown to be carcinogenic, about 25% of cancer deaths in developed countries are due to the carcinogens in the tar of tobacco smoke. Viruses have been known to cause cancer in animals, including humans. Viruses that cause cancer usually carry their own oncogenes, which can cause uncontrolled cell division of the host cells. Burkitt?s lymphoma, for example, is caused by a virus and is the mist common cancer in children in certain parts of Africa. Cervical cancer is an example of a type of cancer that can be transmitted sexually. Some people are said to have a hereditary predisposition to cancer, due to it being common in their families. This provides evidence of a genetic link. In most cases thought the disease itself is not inherited but susceptibility to the factors that cause the disease are. However some forms of cancer do appear to be caused by the inheritance of a single faulty gene. For example, Retionblastoma, which is caused by an error in chromosome 13. It is believe that development of a malignant cancer cell involves several step and is not cause by just one factor, but more than one working over several years.

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