Textbook Question
Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?
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Ch. 15 - Gene Mutation, DNA Repair, and Transposition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776
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Table of contents
- Ch. 1 - Introduction to Genetics17
- Ch. 2 - Mitosis and Meiosis36
- Ch. 3 - Mendelian Genetics51
- Ch. 4 - Extensions of Mendelian Genetics74
- Ch. 5 - Chromosome Mapping in Eukaryotes51
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages46
- Ch. 7 - Sex Determination and Sex Chromosomes33
- Ch. 8 - Chromosome Mutations: Variation in Number and Arrangement40
- Ch. 9 - Extranuclear Inheritance31
- Ch. 10 - DNA Structure and Analysis43
- Ch. 11 - DNA Replication and Recombination44
- Ch. 12 - DNA Organization in Chromosomes30
- Ch. 13 - The Genetic Code and Transcription54
- Ch. 14 - Translation and Proteins47
- Ch. 15 - Gene Mutation, DNA Repair, and Transposition41
- Ch. 16 - Regulation of Gene Expression in Bacteria29
- Ch. 17 - Transcriptional Regulation in Eukaryotes41
- Ch. 18 - Post-transcriptional Regulation in Eukaryotes33
- Ch. 19 - Epigenetics33
- Ch. 20 - Recombinant DNA Technology44
- Ch. 21 - Genomic Analysis36
- Ch. 22 - Applications of Genetic Engineering and Biotechnology36
- Ch. 23 - Developmental Genetics37
- Ch. 24 - Cancer Genetics34
- Ch. 25 - Quantitative Genetics and Multifactorial Traits54
- Ch. 26 - Population and Evolutionary Genetics45
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?
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Begin by identifying the main types of DNA damage caused by UV radiation, such as the formation of thymine dimers, which distort the DNA helix and block replication.
Describe the different DNA repair mechanisms that cells use to fix UV-induced damage, including nucleotide excision repair (NER), base excision repair (BER), and direct repair mechanisms like photoreactivation.
Explain nucleotide excision repair (NER) in detail: how it recognizes bulky lesions like thymine dimers, excises a short single-stranded DNA segment containing the damage, and fills in the gap using DNA polymerase and ligase.
Discuss photoreactivation, a direct repair mechanism where the enzyme photolyase uses energy from visible light to break the bonds of thymine dimers, restoring the original DNA structure without excision.
Clarify the specific role of visible light in photoreactivation: it activates photolyase, enabling it to reverse UV-induced thymine dimers efficiently, which is a unique repair pathway dependent on light energy.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Types of DNA Repair Mechanisms
DNA repair mechanisms are cellular processes that correct damage to DNA molecules. Key types include direct repair, excision repair (base excision and nucleotide excision), mismatch repair, and recombinational repair. Each mechanism targets specific types of damage to maintain genomic integrity.
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05:44
Repair Pathways
UV-Induced DNA Damage
Ultraviolet (UV) radiation primarily causes DNA damage by inducing the formation of pyrimidine dimers, such as thymine dimers, which distort the DNA helix and block replication. Understanding this damage is essential to grasp why specific repair pathways are activated.
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04:29Induced Mutations
Role of Visible Light in Photoreactivation
Visible light drives photoreactivation, a direct repair process where the enzyme photolyase absorbs light energy to break the bonds of UV-induced pyrimidine dimers. This light-dependent repair reverses mutations without excision, highlighting the unique role of visible light in DNA repair.
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Related Practice
Textbook Question
Why are X rays more potent mutagens than UV radiation?
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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
Mammography is an accurate screening technique for the early detection of breast cancer in humans. Because this technique uses X rays diagnostically, it has been highly controversial. Can you explain why? What reasons justify the use of X rays for such a medical screening technique?
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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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Textbook Question
Describe how the Ames test screens for potential environmental mutagens. Why is it thought that a compound that tests positively in the Ames test may also be carcinogenic?
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