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Questions and Answers
What is the role of methyltransferase in DNA damage repair?
What is the role of methyltransferase in DNA damage repair?
Which base pair swap occurs if O6-methylguanine is not repaired?
Which base pair swap occurs if O6-methylguanine is not repaired?
What type of DNA repair involves removing a patch of nucleotides?
What type of DNA repair involves removing a patch of nucleotides?
What triggers the action of DNA glycosylases in base excision repair?
What triggers the action of DNA glycosylases in base excision repair?
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What common chemical reaction is often repaired by the base excision mechanism?
What common chemical reaction is often repaired by the base excision mechanism?
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What is the result of deamination of cytosine in DNA?
What is the result of deamination of cytosine in DNA?
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Which enzyme recognizes the missing base after DNA glycosylase acts?
Which enzyme recognizes the missing base after DNA glycosylase acts?
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What is produced when purine bases are lost from DNA during depurination?
What is produced when purine bases are lost from DNA during depurination?
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What role do DNA polymerase and DNA ligase play in nucleotide excision repair?
What role do DNA polymerase and DNA ligase play in nucleotide excision repair?
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What type of DNA damage does nucleotide excision repair specifically target?
What type of DNA damage does nucleotide excision repair specifically target?
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How does the nucleotide excision repair mechanism identify DNA damage?
How does the nucleotide excision repair mechanism identify DNA damage?
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What condition is associated with a malfunction in the nucleotide excision repair pathway?
What condition is associated with a malfunction in the nucleotide excision repair pathway?
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What can happen if double-strand breaks in DNA are not repaired?
What can happen if double-strand breaks in DNA are not repaired?
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Which of the following can cause double-strand breaks in DNA?
Which of the following can cause double-strand breaks in DNA?
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What type of damage can be caused by intercalating agents like ethidium bromide?
What type of damage can be caused by intercalating agents like ethidium bromide?
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What does the term 'damage bypass' refer to in cellular responses to DNA damage?
What does the term 'damage bypass' refer to in cellular responses to DNA damage?
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What is the consequence of thymine dimers in the context of DNA repair deficiencies?
What is the consequence of thymine dimers in the context of DNA repair deficiencies?
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Which mechanism directly reverses thymine-thymine dimers in DNA?
Which mechanism directly reverses thymine-thymine dimers in DNA?
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How does a DNA helicase contribute to the nucleotide excision repair process?
How does a DNA helicase contribute to the nucleotide excision repair process?
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What is the most severe type of DNA damage that can occur?
What is the most severe type of DNA damage that can occur?
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What is the primary role of mismatch repair in eukaryotic cells?
What is the primary role of mismatch repair in eukaryotic cells?
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Which mutation is commonly associated with hereditary nonpolyposis colorectal cancer?
Which mutation is commonly associated with hereditary nonpolyposis colorectal cancer?
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Which DNA polymerase is responsible for translesion synthesis past TT dimers?
Which DNA polymerase is responsible for translesion synthesis past TT dimers?
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What kind of DNA damage is generated by the loss of a nitrogenous base from a nucleotide?
What kind of DNA damage is generated by the loss of a nitrogenous base from a nucleotide?
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What is a potential outcome of accumulated mutations due to defective mismatch repair?
What is a potential outcome of accumulated mutations due to defective mismatch repair?
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Which type of repair mechanism can directly reverse DNA damage without nucleolytic excision?
Which type of repair mechanism can directly reverse DNA damage without nucleolytic excision?
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Which chemical agent is known for causing an increase in the rate of mutation?
Which chemical agent is known for causing an increase in the rate of mutation?
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Which type of DNA damage typically requires repair due to spontaneous alterations?
Which type of DNA damage typically requires repair due to spontaneous alterations?
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What type of damage does a T-T dimer represent?
What type of damage does a T-T dimer represent?
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What is the significance of methylated cytosines in DNA?
What is the significance of methylated cytosines in DNA?
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Which of the following best describes deamination?
Which of the following best describes deamination?
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What type of DNA damage typically results from UV radiation?
What type of DNA damage typically results from UV radiation?
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What is the primary mechanism through which homologous recombination repairs DNA?
What is the primary mechanism through which homologous recombination repairs DNA?
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During which phases of the cell cycle does homologous recombination primarily occur?
During which phases of the cell cycle does homologous recombination primarily occur?
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What characterizes nonhomologous end joining compared to homologous recombination?
What characterizes nonhomologous end joining compared to homologous recombination?
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Which condition is associated with failures in DNA recombination repair enzymes?
Which condition is associated with failures in DNA recombination repair enzymes?
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What is one main effect of DNA damage on the cell cycle?
What is one main effect of DNA damage on the cell cycle?
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What happens during nonhomologous end joining when DNA is damaged?
What happens during nonhomologous end joining when DNA is damaged?
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Which phases of the cell cycle can DNA damage impact?
Which phases of the cell cycle can DNA damage impact?
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Why is nonhomologous end joining particularly important before DNA has been replicated?
Why is nonhomologous end joining particularly important before DNA has been replicated?
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Study Notes
Mismatch Repair in Eukaryotes
- Original DNA strand identification relies on recognizing nicks in newly synthesized DNA.
- Lynch Syndrome, a hereditary nonpolyposis colorectal cancer, results from mutations in mismatch repair proteins, leading to rapid accumulation of mutations and tumor development.
General Classes of DNA Damage
- Spontaneous DNA damage can occur due to the action of water in cells.
- A mutagen increases mutation rates beyond spontaneous levels.
- Three main DNA damage classes:
- Single base changes
- Structural distortion
- DNA backbone damage
Single Base Changes
- Single base changes affect DNA sequence slightly.
- Deamination, converting 5-methylcytosine to thymine, is a common mutation source.
- Alkylating agents like nitrosamines can create O6-methylguanosine, which mispairs with thymine, potentially causing mutations.
Structural Distortion
- UV radiation causes cyclobutane ring formation between adjacent thymines, leading to T-T dimers that distort the DNA structure.
- Intercalating agents, such as ethidium bromide, insert between DNA bases, causing structural issues.
- Bulky adducts from chemical mutagens can also lead to distortions in DNA structure.
DNA Backbone Damage
- Abasic sites result from the loss of a nitrogenous base, often generated by unstable base adducts.
- Double-stranded DNA breaks, the most severe damage type, can be caused by ionizing radiation and various chemicals.
Cellular Responses to DNA Damage
- Cells can perform damage bypass, damage reversal, or damage removal.
- Translesion synthesis (TLS) allows specialized DNA polymerases to replicate past DNA damage, but with higher error rates.
DNA Repair Mechanisms
- DNA stability is crucial for genetic information, necessitating complex repair processes for spontaneous changes.
- Repair processes include direct damage reversal, excision repair, and double-stranded break repair.
Direct Reversal of DNA Damage
- UV-induced thymine dimers can be repaired directly by DNA photolyase, utilizing light energy.
- Methyltransferase removes methyl groups from O6-methylguanine to restore proper base pairing with cytosine.
Excision Repair Mechanisms
- Base excision repair removes damaged bases via DNA glycosylases, addressing issues like depurination and deamination.
- Nucleotide excision repair addresses larger DNA distortions from various sources, including UV damage and bulky lesions.
Xeroderma Pigmentosum
- Caused by mutations in nucleotide excision repair pathways, leading to extreme UV sensitivity and high skin cancer risk.
Double-Strand Break Repair
- Two main pathways for repairing double-strand breaks: homologous recombination and nonhomologous end joining.
- Homologous recombination uses an undamaged homologous chromosome to accurately repair damage.
- Nonhomologous end joining joins broken ends of DNA with potential nucleotide loss and increased mutation risk.
Cell Cycle Delay Due to DNA Damage
- Eukaryotic cells delay the cell cycle to ensure complete DNA repair, blocking transitions between critical phases (G1 to S, S phase progression, G2 to M) in the presence of damage.
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Description
Explore the critical processes of mismatch repair in eukaryotic cells, focusing on the identification of original DNA strands through nick recognition. This quiz also examines the implications of hereditary nonpolyposis colorectal cancer, particularly Lynch syndrome, highlighting the genetic mutations involved in mismatch repair proteins.
