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Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172당신이 사용하는 게 아니라요?교과서 변경
11장, 문제 34f

Using your knowledge of DNA repair pathways, choose the pathway that would be used to repair the following types of DNA damage. Explain your reasoning.
A cytosine that has been deaminated to uracil

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Identify the type of DNA damage: Deamination of cytosine to uracil is a common type of DNA damage where the amino group of cytosine is removed, converting it into uracil. This results in a base mismatch because uracil is not normally found in DNA.
Determine the appropriate DNA repair pathway: The repair pathway for this type of damage is the Base Excision Repair (BER) pathway. BER is specialized for repairing small, non-helix-distorting base lesions, such as deaminated bases.
Explain the steps of the BER pathway: In the BER pathway, a DNA glycosylase enzyme recognizes and removes the uracil base by cleaving the N-glycosidic bond, leaving behind an abasic site (AP site).
Describe the next steps in the repair process: An AP endonuclease enzyme cleaves the DNA backbone at the abasic site, creating a single-strand break. DNA polymerase then fills in the gap by adding the correct nucleotide (cytosine in this case), and DNA ligase seals the nick in the sugar-phosphate backbone.
Summarize the reasoning: The BER pathway is used because it is specifically designed to recognize and repair small, non-bulky lesions like uracil in DNA, ensuring the integrity of the genetic information.

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DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that correct damage to the DNA molecule. These mechanisms are crucial for maintaining genomic integrity and preventing mutations that can lead to diseases such as cancer. Different types of DNA damage require specific repair pathways, including base excision repair, nucleotide excision repair, and mismatch repair.
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Repair Pathways

Base Excision Repair (BER)

Base excision repair (BER) is a DNA repair pathway that specifically addresses small, non-helix-distorting base lesions, such as deaminated cytosine. In this process, a DNA glycosylase enzyme recognizes and removes the damaged base, creating an abasic site. Subsequently, an endonuclease cleaves the DNA backbone, and DNA polymerase fills in the gap with the correct nucleotide, followed by ligation to restore the DNA strand.
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Repair Pathways

Deamination of Cytosine

Deamination of cytosine is a chemical reaction where an amino group is removed from the cytosine base, converting it into uracil. This alteration can lead to mispairing during DNA replication, as uracil pairs with adenine instead of guanine. If not repaired, this can result in permanent mutations, making the repair of deaminated cytosine critical for maintaining genetic fidelity.
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Base Distortions
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교과서 질문

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교과서 질문

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A double-strand break that occurs just after replication in an actively dividing cell

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교과서 질문

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A double-stranded break that occurs during G1 and prevents completion of DNA replication

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교과서 질문

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A thymine dimer induced as a result of UV exposure

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Ataxia telangiectasia (OMIM 208900) is a human inherited disorder characterized by poor coordination (ataxia), red marks on the face (telangiectasia), increased sensitivity to X-rays and other radiation, and an increased susceptibility to cancer. Recent studies have shown that this disorder occurs as a result of mutation of the ATM gene. Propose a mechanism for how a mutation in the ATM gene leads to the characteristics associated with the disorder. Be sure to relate the symptoms of this disorder to functions of the ATM protein. Further, explain why DNA repair mechanisms cannot correct this problem.
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교과서 질문

A geneticist searching for mutations uses the restriction endonucleases SmaI and PvuII to search for mutations that eliminate restriction sites. SmaI will not cleave DNA with CpG methylation. It cleaves DNA at the restriction digestion sequence ↓ 5′−CCC GGG−3′ 3′−GGG CCC−3′ ↑ PvuII is not sensitive to CpG methylation. It cleaves DNA at the restriction sequence ↓ 5′−CAG CTG−3′ 3′−GTC GAC−5′ ↑ What process is the researcher intending to detect with the use of these restriction enzymes?

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