Exogenous or external processes and internal metabolic processes of the body contribute thousand to a million DNA damaging events per day (Dexheimer, 2013; Sigma-Aldrich, 2007). Errors, damages and chemical changes of the DNA molecules are identified and corrected in the DNA repair process. DNA repair involves the identification of DNA errors and maintenance of the errors to prevent cell death or remove cancerous cells (Sixth framework programme, 2009).
Mismatches of the nitrogenous bases, breaks in the backbone and crosslinks of the covalent linkages between the bases are common types of DNA damage (users.rcn.com, 2013). Direct DNA damage or crosslinking between adjacent cytosine and thymine bases creating pyrimidine dimers is caused by UV-B and indirect damage or free radicals formation is caused by UV-A (University of Leicester, 2010). Processes such as replication or transcription can be affected by DNA damage and mutations can be induced causing cancer (Dexheimer, 2013).
UV-radiation, gamma rays, X-rays, oxygen radicals and other chemicals act as agents to damage the DNA molecules (users.rcn.com, 2013). Chemical causing DNA damage includes alkylating agents such as methyl methanesulfonate, temozolomide, nitrogen mustards, chemotherapeutic drugs such as topoisomerase I or II inhibitors and other chemicals such as N-nitrosomines, heterocyclic amines and benzo-a-pyrenre (Dexheimer, 2013). According to University of Leicester (2010), industrial chemicals such as vinyl chloride and hydrogen peroxide, and environmental chemicals such as polycyclic hydrocarbons cause DNA damages. DNA repair mechanisms include base excision repair, mismatch repair, nucleotide excision repair and double strand break repair (Dexheimer, 2013; Sixth framework programme, 2009).
Dexheimer, T.S. (2013) DNA Repair Pathways and Mechanisms. Mathews, L.A. (eds)(2013) DNA Repair of Cancer Stem Cells. Springer. [Online] Available at www.springer.com [Accessed on 26 March 2014].
Sixth Framework Programme (2009) DNA Damage Response and Repair Mechanisms [Online] Available at http://www.dna-repair.nl [Accessed on 29 March 2014].
Sigma-Aldrich (2007) DNA Damage and Repair [Online] Available at www.sigmaaldrich.com [Accessed on 20 March 2014].
University of Leicester (2010) DNA Replication and Repair [Online] Available at www2.le.ac.uk [Accessed on 29 March 2014].
Users.rcn.com (2013) DNA Repair [Online] Available at http://www.users.rcn.com [Accessed on 20 March 2014].