Risk of Cancer: When harmful chemicals enter our cells, the cellular response is to try to change them into harmless substances and eliminate them from the body. The chemicals which are highly poisonous or toxic are very reactive and immediately react with the key molecules in the cell causing death of the cell. This may damage the organ and perhaps kill the person as well.
The amount of any carcinogen we are exposed to at a given time, is too small to cause such a drastic effect. The cells then try to convert the tiny amounts of these chemicals, in a step-wise manner to less harmful substances.
Risk of Cancer
A number of enzymes called detoxifying enzymes carry out this job. A substance entering the cells may be carcinogenic by itself and react with the molecules in the cells.
It is also possible that this substance may not be a carcinogen but may be converted into a carcinogen by detoxifying enzymes before it is made harmless. If this reaction occurs slowly, the carcinogenic substance will remain in the cell for a longer time and will have better chance to react with cellular molecules. In a large number of cases, these carcinogens react with the cell’s DNA and get attached to it. These molecules attached to the DNA form, what are called, ‘DNA adducts’ and damage the DNA. The cells normally have machinery to repair damage to DNA. There are a number of repair systems which carry out this work. Some remove the adducts. The repair system also removes a part of that strand of DNA which has been damaged. Then it uses a mechanism similar to that used in DNA replication to repair the breach. But such a system is prone to making mistakes. If a wrong base is put in the DNA during repair, it may change the code just like a mutation would. Thus, mutations get introduced during repair of damage caused by carcinogens.
If such mutations occur in oncogenes or suppressor genes, it can convert a normal cell into a cancer cell. It has now been shown that when cells are treated with certain hydrocarbons, they cause a mutation in the ras onco-gene at a specific codon which activates this oncogene. This mutation has been found in a large number of human tumors also. This is very good evidence that carcinogens can cause specific mutations.
Therefore, our ability to detoxify carcinogenic substances becomes important. There are several enzyme systems and the rate of detoxification by enzymes varies. A mutation in the gene for a specific enzyme may change it from fast to a slow acting one. If the enzyme acts at slow rate, a carcinogen will remain in the cell for a longer time and will be more likely to cause damage. This has been shown for an enzyme called N-acetyl-transferase in human populations. If two people are exposed to the same amount of carcinogen, the person who acetylates slowly is more likely to develop cancer. In other words, such a person will have a higher risk of cancer.