What environmental factors damage DNA?

Answer 1

There are many common types of DNA damage that impact accurate replication by DNA polymerases . Furthermore, the degree and spectrum of DNA damage depends on the sample source and the type of environment to which it was exposed. Some types of damage are ubiquitous and can potentially be present in all extracted DNA, while other types of damage are the result of exposure to a specific source (see Table 1). Under hysiological conditions the most labile bond in DNA is the N-glycosyl bond that attaches the base to the deoxyribose backbone. This is in contrast to RNA in which the phosphodiester bond in the backbone is the least stable under the same conditions. Hydrolysis of the N-glycosyl bond results in the loss of a base leaving an rinic/apyrimidinic (AP) site that itself eventually decomposes into a nick. Because the reactive species is H2O, AP sites are expected in all stored DNA samples. This includes lyophilized samples because it is very difficult to remove the final shell of H2O molecules immediately adjacent to the DNA. Under metabolically active conditions it is estimated that approximately 2,000-10,000 AP sites are formed in a single human cell genome each day . This rate will vary from sample to sample, especially in samples taken from a crime scene because the type of environmental exposure will vary. The presence of AP sites in a DNA sample is problematic for two primary reasons. First, genetic information is lost because the AP site cannot form a base pair with an incoming nucleotide during DNA replication. Second, typical PCR polymerases stall at the AP site preventing further replication .If enough AP sites are present, amplification or sequencing reactions will simply fail. The breakdown of AP sites into nicks further compounds the problem as it eventually leads to the fragmentation of the DNA. Another common type of DNA damage that occurs under physiological conditions is the hydrolytic deamination of cytosine to form uracil .Sequencing studies on DNA extracted from very old samples, termed ancient DNA, have determined that this is the major damage complicating data analysis.Cytosine deamination, like AP site formation, is caused by hydrolysis and is probably present in the DNA extracted from many sources. Interestingly, unlike depurination, the rate of cytosine deamination is slowed in double-stranded DNA as compared to single stranded DNA.

Answer 2

Environmental factors that can damage DNA include exposure to ultraviolet (UV) radiation from the sun, certain chemicals and pollutants in the air and water, cigarette smoke, and ionizing radiation from sources like X-rays or radioactive materials. These factors can lead to DNA mutations and other types of damage that may increase the risk of cancer and other health problems.