Alkylating agents cause mutations by chemically altering bases so that they pair up with a specific base other than the normally complementary base. Intercalating agents are planar molecules that can insert themselves between the stacked bases within the double helix. These agents alter the molecule of DNA in such a way that DNA polymerases may insert or skip one or more bases during replication, often resulting in frameshift mutations. For example, proflavin, acridine orange, and ethidium bromide are intercalators.
When ultraviolet light is absorbed by adjacent pyrimidines in one strand of a DNA molecule, a dimer forms. These dimers interfere with proper base pairing during DNA replication. The impact is so extensive that the normal replicative process is stopped until these dimers are repaired.
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