DNA Mutation

Heritable changes in the DNA sequence has been defined as DNA mutation.  DNA damaging agents such as X-rays, UV-rays or chemical might cause DNA mutation. Natural processes in the cell may result a spontaneous mutation and reaction between mutagen and DNA can cause induced mutation (KSU, n.d.). Hereditary mutations or germline mutation can be passed to next generation from parent to child and it remains in the individual’s body throughout the life however somatic or acquired mutation caused by external factors cannot be passed onto next generation (NIH, 2014).

Mutation can be transition or transversion. In transition, purine nucleotide is changed into purine and pyrimidine into pyrimidine whereas purine is changed into pyrimidine and vice versa in transversion mutation (Chuck and Chao, n.d.). Insertion, deletion and substitution are DNA mutation mechanisms. Nitrogenous base is replaced in substitution by other bases, deletion is the loss of the block of one or more DNA pairs and insertion is the addition of the block of one or more DNA (Berkeley, n.d.).

Mutation can have health effects on human body. Normal development of body and development of embryo at its early stages can be affected by mutation (NIH, 2014). Mutation can also induce protein malfunction and genetic disorder (NIH, 2014). Deletion occurring between repeated sequences has resulted changes in mitochondrial structure and disorder of central nervous system known as mitochondrial encephalomyopathies (immuneweb, n.d.).

Depurination and deanimation can lead to spontaneous lesions causing DNA damage and mutation. Depurination is the interruption of the glycosidic bond between the base and deoxyribose and the subsequent loss of a guanine and an adenine residue from the DNA. Deanimation includes the conversion of G-C pair into an A-T pair (Immuneweb, n.d.).

 

References

Berkeley (n.d.) Types of Mutations and their impact on protein function [Online] Available at http://www.mcb.berkeley.edu [Accessed on 22 May 2014].

Chuck, G. and Chao, K (n.d.) Mutation [Online] Available at http://www.memocgu.tw [Accessed on 13 May 2014].

Immuneweb (n.d.) Mechanisms of Gene Mutation [Online] Available at http://www.immuneweb.com [Accessed on 25 May 2014].

KSU (n.d.) DNA Mutation [Online] Available at http://www.faculty.csu.edu.sa [Accessed on 22 May 2014].

Marinus, M.G. (n.d.) Mutation [Online] Available at http://www.users.umass.edu [Accessed on 13 May 2014].

National institute of Health (NIH) (2014) Mutation and Health [Online] Available at http://www.ghr.nlm.nil.gov [Accessed on 22 May 2014]

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DNA Methylation

DNA Methylation is an epigenetic mechanism with addition of methyl group into nitrogenous bases of DNA. The mechanism involves the transfer of methyl group into the C5 position of the cytosine and formation of 5-methylcystosine (Moore et al., 2013). DNA Methylation facilitates X-chromosome inactivation, imprinting and suppression of parasitic DNA sequences however methylation increases the rate of mutation (Robertson and Jones, 1999). Cell functions are affected by epigenetic regulation of gene expression. Genomic stability and mammalian development have been associated with methylation pattern (Tost, 2009).

Prediction and monitoring the response to antineoplastic treatment, detection of cancer at early stages and classification of tumour can be carried out with the help of DNA methylation pattern (Tost, 2009). Enzymes responsible for DNA methylation have been categorised into writers, erasers and readers by Moore et al (2012). Addition of methyl groups onto cytosine is categorised by writers, modification and removal of the methyl group is conducted by erasers and readers influence gene expression (Moore et al., 2012).

In the human genome, CpG or Cytosine (C) linked by a phosphate bond to the base Guanine (G) dinucleotide is methylated and methylation causes suppression of gene expression in the cells. (Lim and Maker, 2010; Robertson and Jones, 1999). Methylation and epigenetic changes has adverse effects on cancer cells. DNA Methylation has been believed to have direct role in carcinogenesis (Robertson and Jones, 1999). Deamination of methylated cytosine converts cytosine to thymine leading to inactivation of tumour suppression genes (TSGs), a vital factor for normal growth and differentiation (Lim and Maker, 2010).

 

References

Moore, L.D., Le, T., Fan, G. (2012) DNA Methylation and Its Basic Function Neuropsychopharmacology Reviews, pp 1-16.

Robertson, K.D. and Jones, P.A. (1999) DNA Methylation: Past, Present and Future Directions, Carcinogenesis, Vol. 21 (3), pp. 461-467.

Lim, D.H.K. and Maker, E.R. (2010) The Obstetrician and Gynaecologist. Vol 12, pp. 37-42.

Tost,J. (2009) DNA Methylation:  An Introduction to the Biology and Disease-Associated Changes of a Promising Bio-marker Methods, Molecular Biology, Vol 507, pp. 3-20.