A cell turns to cancerous stage due to accumulation of mutation in the genome. The genome consists of strands of DNA and in turn is a string of four chemical moieties arranged in a particular sequence. An abrupt and spontaneous change in the sequence is known as mutation and if the mutation takes place in the area producing functionally important products that control cell multiplication then the cell enters into cancerous condition or a condition of uncontrolled cell division. Even though the cells possess innate mechanism to rectify the error, slippage of the cell to carry out the repair mechanism can result in onset of caner. There are many agents natural as well as synthetic that induce mutation. Such agents are known as mutagens. About 10% of the cancer cases can be attributed to the heritable factors and some other cancer types are caused by the viruses. Thus cancer is caused by three major factors, 1) mutations in the genetic material, 2) viral infections and 3) hereditary factors.
Types of Mutation
Mutation can be broadly divided into two types- spontaneous and induced. Spontaneous mutations are those occurring naturally and the induced mutations are the ones due to the action of mutagens.
Causative agents
Induced mutations can be caused by the effect of physical factors such as radiations, mainly UV, cosmic and also due to low energy radiations and chemical mutagens such as formaldehyde, asbestos, number of compounds present in cigarette smoke, nitrous acid, colchicines, ethyl methyl sulphonate (EMS), certain types of pesticides etc.
Prolonged exposure of low energy radiations can also induce mutations in the body that gradually convert the cells to cancerous. Ionizing radiations such as X-rays, gamma rays are responsible for cancer. Along with these synthetic forms, certain types of naturally derived compounds such as mustard gas and phytochemicals are also responsible for cancer. Peoples working in coal tar mines, distillations units and gasification plants are prone to cancer due to the effect of coal tar and its derivatives. Those handling metal ores and smelting are more exposed to arsenic, which is a mutagen. A group of mutagenic chemicals under polycyclic aromatic hydrocarbons are in high concentration at petroleum refineries and those working in such places are also prone to cancer.
Cancer from viruses
Research works on the basic mechanism of cancer has revealed that there are certain genes in a cell, which on mutation can make the cell prone to cancer. Such genes are proto-onco genes. Its mutated part will be present in certain types of viruses, which on infection injects those genes into the genome of cells. Such cells afterwards turn cancerous. These viruses are generally named as tumour viruses eg. HTLV-1, hepatitis B virus, Epstein Barr virus etc. |
