DNA Damage Caused by Ultraviolet Radiation

By: Nicolle A. Rosa Mercado

Introduction-DNA: -Most important molecule for every living organism

-Contains the instructions necessary for every living organism to function

-Alterations in it may lead to genetic disorders and cancer

-Ultraviolet (UV) radiation: -Uncontrollable environmental factor that alters DNA sequences

-Its damage may cause cells to restrain RNA synthesis (Moné MJ et. al 2001)

Fig. 1: This image is an example of a possible alteration in a DNA sequence.

earthobservatory.nasa.gov

UV Radiation-Type of electromagnetic radiation that has a shorter wavelength than that of the visible light.

-Three types of UV radiation: - UV-A (400nm-315nm): found in black lights - UV-B (315nm-280nm): most dangerous type - UV-C (280nm-200nm): germicidal

Fig. 2: This image is an explanation of the lightspectrum

flightspectrumllc.com

How UV radiation may be beneficial

-May create resistance to certain pathogens in plants

-Used as a treatment for people with vitiligo for humans

-Used to purify drinking water due to its germicidal properties

-Helpful in studies that involve spectophotometry and molecular genetics.

Fig. 3: This image shows the hands of a vitiligo patient. UV-B light is used to restore the pigmentation of their skin.

Fig. 4: This image shows the machinery used to purify drinking waterwith UV radiation

Cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts(6-4 PPs)

-Lesions in the DNA sequence caused by UV exposure (De Lima-Bessa KM et. al. 2007)

-May be responsible for the formation of clusters that might lead to skin carcinomas

-Promote apoptosis provoked by UV exposure in cells that lack NER

-Can obstruct DNA transcription and replication

-Fixed through DNA repair mechanisms

DNA Repair Mechanisms-Cannot always detect the mutations due to defects in the repair mechanisms themselves

-Important for maintaining the DNA sequence stable.

-A type of DNA repair mechanism is nucleotide excision repair (NER), which corrects different types of damages including thymine dimers provoked by UV radiation.(http://www.nature.com/scitable/topicpage/dna-damage-repair-mechanisms-for-maintaining-dna-344)

NER Flow Chart

Fig. 5: This image shows how NER works. It consists of four proteins UvrA, UvrB, UvrC, and UvrD. UvrA and UvrB search for mutations in the sequence, UvrC makes cuts in the region of mutations so UvrD can remove them from the sequence. DNA polymerase and DNA ligase then restore the sequence to the way it was before the mutation occurred.

http://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation33.html

UV radiation and cancer-Three types of cancer caused by UV radiation:

-Basal Cell Carcinoma: innermost part of the epidermis; not a big threat

-Squamous Cell Carcinoma: upper part of the epidermis; not a big threat

-Melanoma: most dangerous type of skin cancer; develops in skin cells known as the melanocytes

UV radiation and cancer

Fig.6: This image shows how squamous cell carcinomas and basal cell carcinomas look on the outer part of the epidermis.

Fig. 7: This image demonstrates how melanoma affects the inner and outer epidermis and the dermis.

-It is very important to understand this topic due to the fact that UV radiation is an uncontrollable factor that can affect our health in a great way.

-Understanding how UV radiation relates to DNA repair mechanisms might help with the discovery of new techniques to maintain stability in DNA sequences.

Importance of this study

Conclusion

-DNA is the most important molecule in every organism and it is highly susceptible to UV radiation.

-Although DNA has highly specific repair mechanisms, some mutations caused by UV can be ignored due to a defect in the repair mechanism.

-Ultra-violet radiation causes DNA damage such as CPDs and 6-4 PPs that may lead to cancer.

-Melanoma is the most dangerous type of skin cancer.

-UV radiation presents a mayor threat to our health because of its ability to damage DNA sequences.

References

-Bernard A. Kunz, Paige K. Dando, Desma M. Grice, Peter G. Mohr, Peer M. Schenk, and David M. Cahill, (October 2008), UV-Induced DNA Damage Promotes Resistance to the Biotrophic Pathogen Hyaloperonospora parasitica in Arabidopsis, Rockville, United States, American Society of Plant Biologists,148:1021-1031

-de Lima-Bessa KM, Armelini MG, Chigancas V, Jacysin JF, Amarante-Mendes GP, Sarasin A, Menck CFM, (December 2007), CPDs and 6-4PPs play different roles in UV-induced cell death in normal and NER-deficient human cells, Brazil, DNA Repair, 7:303-312

-Hidawi. June 2010. India. September 2010. Available at:http://www.hindawi.com/journals/jna/2010/592980/

-Moné MJ, Volker M, Nikaido O, Mullenders LHF, van Zeeland AA, Vershure PJ, Manders EMM, van Driel R, (September 2001), Local UV-induced DNA damage in cell nuclei results in local transcription inhibition, Amsterdam, EMBO Reports, 21:1013-1017

-Nijhofa JGW, Muldera, Aat M, Speksnijderb, Ewoud N, Hoogervorstb, Esther M, Mullendersc, Leon HF, De Gruijl, Frank R, (July 2007), Growth stimulation of UV-induced DNA damage retaining epidermal basal cells gives rise to clusters of p53 overexpressing cells, The Netherlands, DNA Repair 6:1642-1650

-Oh K, Bustin M, Mazur S, Appellac E, Kraemer K, (September 2010), UV-induced histone H2AX phosphorylation and DNA damage related proteins accumulate and persist in nucleotide excision repair-deficient XP-B cells, United States, DNA Repair, 10:5-15.

-Scitable. 2008. Nature Education. 2008. Available at: http://www.nature.com/scitable/topicpage/dna-damage-repair-mechanisms-for-maintaining-dna-344

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