Textbook Question
Why are X rays more potent mutagens than UV radiation?
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Ch. 15 - Gene Mutation, DNA Repair, and Transposition
Chapter 15, Problem 14
Contrast the various types of DNA repair mechanisms known to counteract the effects of UV radiation. What is the role of visible light in repairing UV-induced mutations?
Verified Solution
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DNA Repair Mechanisms
DNA repair mechanisms are cellular processes that identify and correct damage to the DNA molecules that encode an organism's genome. These mechanisms are crucial for maintaining genetic stability and preventing mutations. Key types include nucleotide excision repair, which removes bulky DNA adducts, and photoreactivation, which directly reverses UV-induced damage.
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Repair Pathways
Nucleotide Excision Repair (NER)
Nucleotide excision repair (NER) is a DNA repair mechanism that removes a wide range of DNA lesions, including those caused by UV radiation. In NER, damaged DNA is excised and replaced with the correct nucleotides, restoring the original sequence. This process is essential for preventing mutations that can lead to skin cancer and other diseases associated with UV exposure.
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Photoreactivation
Photoreactivation is a light-dependent DNA repair process that specifically targets UV-induced pyrimidine dimers, which are covalent linkages between adjacent thymine or cytosine bases. This mechanism involves the enzyme photolyase, which, upon absorbing visible light, catalyzes the cleavage of these dimers, effectively reversing the damage without the need for excision and resynthesis.
Related Practice
Textbook Question
DNA damage brought on by a variety of natural and artificial agents elicits a wide variety of cellular responses involving numerous signaling pathways. In addition to the activation of DNA repair mechanisms, there can be activation of pathways leading to apoptosis (programmed cell death) and cell-cycle arrest. Why would apoptosis and cell-cycle arrest often be part of a cellular response to DNA damage?
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Textbook Question
A glycine residue is in position 210 of the tryptophan synthetase enzyme of wild-type E. coli. If the codon specifying glycine is GGA, how many single-base substitutions will result in an amino acid substitution at position 210? What are they? How many will result if the wild-type codon is GGU?
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Textbook Question
Refer to Figure 13.7 to respond to the following:
A base-substitution mutation that altered the sequence shown in part (a) eliminated the synthesis of all but one polypeptide. The altered sequence is shown here:
5'-AUGCAUACCUAUGUGACCCUUGGA-3'
Determine why.
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Textbook Question
The family of a sixth-grade boy in Palo Alto, California, was informed by school administrators that he would have to transfer out of his middle school because they believed his mutation of the CFTR gene, which does not produce any symptoms associated with cystic fibrosis, posed a risk to other students at the school who have cystic fibrosis. After missing 11 days of school, a settlement was reached to have the boy return to school. What ethical problems might you associate with this example?
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Textbook Question
A significant number of mutations in the HBB gene that cause human β-thalassemia occur within introns or in upstream noncoding sequences. Explain why mutations in these regions often lead to severe disease, although they may not directly alter the coding regions of the gene.
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