Spontaneous and Induced Mutations

Random errors during DNA replication can cause mismatches or base loss, leading to spontaneous mutations.

Lesions from reactive oxygen species can induce depurination and depyrimidination in the DNA backbone, creating apurinic and apyrimidinic sites that may lead to spontaneous mutations.

Tautomeric shifts alter base pairing by converting nitrogenous bases from keto to enol or amino to imino forms, causing spontaneous mutations.

While spontaneous mutations occur naturally, chemical mutagens like base analogs can cause mutations too.

5-bromouracil is a thymine analog that can pair incorrectly with adenine and guanine, causing heritable mutations.

Modifying agents, such as nitrous acid, alter adenine to pair with cytosine, disrupting normal base-pairing.

Intercalating agents, such as ethidium bromide, insert themselves between stacked DNA bases, distorting the DNA helix.

Physical mutagens, such as ultraviolet radiation, damage DNA by forming thymine dimers, which hinder DNA polymerase activity.

Finally, ionizing radiation, including X-rays, causes both single–and double-stranded breaks in DNA, leading to severe chromosomal mutations.