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BioDiscovery, 2014

Journal of Bacteriology, 2003

The American Journal of Pathology, 1998

Current Biology, 1996

Unit-2 Introduction to DNA Damage and Repair: DNA is a highly stable and versatile molecule. Though sometimes the damage is caused to it, it is able to maintain the integrity of information contained in it. The perpetuation of genetic material from generation to generation depends upon keeping the rates of mutation at low level. DNA has many elaborate mechanisms to repair any damage or distortion. The most frequent sources of damage to DNA are the inaccuracy in DNA replication and chemical changes in DNA. Malfunction of the process of replication can lead to incorporation of wrong bases, which are mismatched with the complementary strand. The damage causing chemicals break the backbone of the strand and chemically alter the bases. Alkylation, oxidation and methylation cause damage to bases. X-rays and gamma radiations cause single or double stranded breaks in DNA. A change in the sequence of bases if replicated and passed on to the next generation becomes permanent and leads to mutation. At the same time mutations are also necessary which provide raw material for evolution. Without evolution, the new species, even human beings would not have arisen. Therefore a balance between mutation and repair is necessary. Types of Damage: Damage to DNA includes any deviation from the usual double helix structure. 1. Simple Mutations: Simplest mutations are switching of one base for another base. In transition one pyrimidine is substituted by another pyramidine and purine with another purine. Trans-version involves substitution of a pyramidine by a purine and purine by a pyrimidine such as T by G or A and A by C or T. Other simple mutations are detection, insertion of a single nucleotide or a small number of nucleotides. Mutations which change a single nucleotide are called point mutations. 2. Deamination: The common alteration of form or damage includes deamination of cytosine (C) to form uracil (u) which base pairs with adenine (A) in next replication instead of guanine (G) with which the original cytosine would have paired.

Cell Cycle, 2016

Photochemistry and Photobiology, 1985

Journal of toxicology and environmental health. Part A, 2011

Molecular Epidemiology of Chronic Diseases, 2008