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DNA becomes damaged (in the sense of its information capacity) when it mutates (or deviates) from its original form. There are many known substances which are DNA mutagens; among them are: oxidizing agents, alkylating agents and electromagnetic radiation. Damage by these agents includes such difficulties as: cross linking between the pyrimidine bases, base modifications and double strand breaks.
Genetic mutation is said to occur when a selective (natural or synthetic) change occurs to the DNA molecule, affecting replication as well as information transmission. Effectively, this alters the manner in which DNA interacts with other proteins, as well as the manner in which it 'codes' the creation of proteins themselves. Although the cells have means of repairing DNA structurally, it is not always possible to repair all of the damage before abnormalities occur. Generally, the effect of these abnormalities lead to genetic disorders and physical cancers.
A particular biological bi-product of the interaction between ultra violet light and DNA is a 'thymine dimer' (TD). A TD refers to the covalent bonding of two adjacent thymine residues, cause a 'kink' in the physical DNA structure itself. This type of behaviour can often be modified or repaired before the DNA replicates and spreads its genetic information. However, this is not always the case, and sometimes these abnormalities can lead to certain types of cancers such as skin cancer.
Typically caused through oxidation, this particular type of genetic abnormality, also known as DNA methylation, causes alteration to the physical DNA sequence without altering the overall 'shape' of the DNA itself. Methylation refers to the addition of a methyl group to a molecule. In this case, the molecule is DNA, or more specifically, the molecules in question are the bases attached to the polymer rungs of the helix. Generally, once one of the bases becomes methylated, it becomes unreadable, and the DNA sequence is altered, and different proteins or even unusable proteins are produced.
Double Strand Breaks:
Possibly the most dangerous type of oxidative damage, a double strand break can lead to 'point mutations', 'insertions' and 'deletions' as well as 'chromosonal translocations'. Chromosomal translations exists when a rearrangement of parts between chromosomes occurs.A translocation is said to occur when a 'fusion gene' unites two otherwise separated gene sequences. This type of abnormal behaviour is said to cause cancer,
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