Repair and Mutagenesis of DNA

Abstract

During their lifetime, all the cells of a living organism are exposed constantly to harmful agents such as radiations and chemicals. DNA (deoxyribonucleic acid), a crucial cell constituent, is highly sensitive to deleterious agents. A large majority of cells survive when exposed chronically at low doses since DNA damage induces cell enzymes that repair DNA lesions. Repair acts very efficiently when DNA stops replicating after the occurrence of lesions. After repair has taken place, DNA replication resumes, followed by cell division. While various repair processes concur to restore cell survival, each of them is never completely efficient and lesions remain in the DNA, acting as stepping-stones. Resumption of DNA synthesis on the strand opposite the remaining lesions permits the bypassing of these obstacles. A process, called trans-lesion DNA synthesis is one of the most efficient processes generating mutations. Mutations come into view in cells that survive the DNA-damaging treatment.

In short, a mutation is a DNA change that is recorded durably and passed on to the offspring after replication. A number of mutations in germ cells have harmful effects for they often cause hereditary diseases. Similarly, mutations that accumulate in dividing body cells (somatic cells) can generate cancers. Yet, most of the occurring mutations behave as neutral in their usual environment. Selection forces the genome to retain the beneficial mutations.