9. Xeroderma pigmentosum (XP) is an autosomal, recessive genetic condition cause
ID: 209073 • Letter: 9
Question
9. Xeroderma pigmentosum (XP) is an autosomal, recessive genetic condition caused by the inability of afflicted individuals to repair DNA damage that is caused by exposure to the sun's ultraviolet rays Exposure of ultraviolet radiation alters the shape of our DNA by causing an abnormal bond to form with the DNA molecule itself. Describe the type of bond that forms in our DNA as a result of sun exposure. b. In a normal person, what type of DNA repair is used to correct damage that is caused by sunlight? e Explain why individuals with XP are unable to use this DNA repair process d What are the symptoms of XP? e What are ways to manage this genetic condition?Explanation / Answer
1.
UV radiation causes two classes of DNA lesions: cyclobutane pyrimidine dimers (CPDs, and 6-4 photoproducts (6-4 PPs). Both of these lesions distort DNA's structure, introducing bends or kinks and thereby impeding transcription and replication. Relatively flexible areas of the DNA double helix are most susceptible to damage.
The exposure of sun causes formation thymidine dimers.
Nucleotide excision Repair and photoreactivation are not the only methods of DNA repair. For instance, base excision repair (BER) is the predominant mechanism that handles the spontaneous DNA damage caused by free radicals and other reactive species generated by metabolism. Bases can become oxidized, alkylated, or hydrolyzed through interactions with these agents. For example, methyl (CH3) chemical groups are frequently added to guanine to form 7-methylguanine.
2.
Normally, the cyclopyrimidine dimers and 6-4 Photoproduct are both repaired through a process known as nucleotide excision repair (NER).These complex process relies on the products of approximately 30 genes. Xeroderma pigmentosum is caused by mutations in genes that are involved in repairing damaged DNA.
The genes involved in DNA repair (NER) perform the following important functions:
· Recognize that DNA damage has occurred
· Unwind portions of DNA where the damage has occurred
· Cut out (excise) the abnormal areas, and
· Replace the damaged portions with the normal DNA.
Thus, inherited defects in the NER-related genes (7 genes) prevent cells from carrying out one or more of these steps. And that is why an individual with the XP is unable to use this DNA repair process
3.
People with xeroderma pigmentosum experience skin symptoms and changes from being in the sun. These may include:
1. unusually severe sunburn that may include blistering after only being in the sun a short time
The name “xeroderma pigmentosum” means “dry pigmented skin.” Exposure to the sun over time causes the skin to become darker, dry, and parchment-like. Even in children, the skin looks like the skin of farmers and sailors who have been in the sun for many years.
4.
Xeroderma pigmentosum is a chronic lifelong condition with no cure. It can be controlled effectively by the following measure
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