9. What are PAHs? Where do you find them? AND Why do they interact with DNA? b.
ID: 276412 • Letter: 9
Question
9. What are PAHs? Where do you find them? AND Why do they interact with DNA? b. Why is it that some people who have been exposed to carcinogens (such as PAH) for a lifetime never develop cancer, but another person, exposed to a small dose of carcinogens may develop cancer at an early age? (Assume genetic propensity is not a factor.) c. Explain how PAHs can cause a cell to become a tumor cell. d. Although PAHs can cause cancer, PAH compounds can also be used to cure cancer. Explain how PAH can kill cancer cells. How is this different than PAH causing cancer?Explanation / Answer
Please find the answers below:
Answer a: PAH or polycyclic aromatic hydrocarbons are complex organic aromatic hydrocarbons containing one or more than one napthalene, anthracene or phenenthrene ring in their structure. These heavy molecules are known to interact with the DNA by intercalating themselves between the nitrogenous bases or the two anti-parallel strands thus making a stable adduct. This adduct intereferes with not only opening of the DNA helix but also impairs replication, hence mutations arise.
Answer b: The PAHs are very diverse in their abundance and concnetration. However, exposure of PAHs is not always associated with cancerous growth. This is because every individual is carried with its own content of genetic propensity and ability to heal the DNA damages. More is the ability of the individual to repair these damages, less likely is to develop cancer. Hence, some people who are frequently exposed to PAHs do not develop cancer while some develop within a few exposures.
Answer c: When the PAH intercalates itself into the DNA, it impairs normal DNA replication. This causes formation of a mis-match site and this mis-match might run a few nucleotides long. Thus, a mutation arises in the subsequent cellular generations. These mutations are often known to cause cancerous growth in cells by turning the proto-oncogenes "on".
Answer d: Modern therapeutics consider that use of PAHs can be made actually to treat cancerous cells as well. It is a very well known fact that the cancerous cells undergo rapid cell division, hence DNA replication. Thus, use of any strategy which prevents DNA replication would prevent cancer growth. Since PAHs impair normal DNA replication, they are thus used to prevent replication of the cancer cell DNA and hence prevent the disease.
This represents another function of the PAHs in clinical management as opposed to their usual effect of pathogencity.
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