Which of the following mechanisms can be used when no template DNA is available to repair DNA damage? (1 mark)

Question

BlackTom AI · Accepted Answer

Nonhomologous end joining (NHEJ) repairs double‑strand breaks without using a homologous DNA template.

1. Relevant knowledge points and concepts
- Double‑strand breaks (DSBs) can be repaired by two major pathways: homologous recombination (HR) and nonhomologous end joining (NHEJ).
- HR requires a homologous DNA sequence (usually the sister chromatid) to serve as a template for error‑free repair and therefore is active in S/G2 phases.
- NHEJ directly ligates broken DNA ends without a homologous template; it functions throughout the cell cycle but is especially important in G1 when no sister chromatid is available.
- Mismatch repair (MMR) corrects replication errors using strand discrimination mechanisms and relies on the complementary strand as a correct template locally.
- Base excision repair (BER) removes and replaces single damaged bases using the intact complementary strand as the template for gap filling.

2. Step‑by‑step reasoning
- The question asks which mechanism can be used when no template DNA is available.
- HR is eliminated because it explicitly requires a homologous sequence (sister chromatid) as the template.
- MMR and BER are single‑strand/lesion‑specific repair systems that use the complementary strand as a template for accurate repair; they are not pathways for repairing two‑ended DSBs in the absence of a template.
- NHEJ is the pathway designed to rejoin broken DNA ends without needing a homologous template.

3. Calculations / intermediate steps
- No numerical calculations are required. The logical intermediate steps are: identify the lesion type (DSB) → determine availability of template (none) → select repair pathway that does not require template (NHEJ).

4. Why the correct answer is correct
- NHEJ binds broken DNA ends (Ku70/80), protects and processes them (DNA‑PKcs, Artemis), and ligates them (XRCC4–Ligase IV) without copying from a homologous sequence. This makes NHEJ the appropriate mechanism when a template is unavailable.

5. Why other options are incorrect
- a. Homologous recombination repair: incorrect because it requires a homologous template (sister chromatid).
- c. Mismatch repair: incorrect because it corrects replication mismatches using the complementary strand and is not a DSB pathway without template.
- d. Base excision repair: incorrect because BER fixes single damaged bases and uses the opposite strand for accurate resynthesis; it is not used to rejoin DSBs without a template.

6. Conclusion
Nonhomologous end joining (option b) is the correct answer, matching the provided answer.

Which of the following mechanisms can be used when no template DNA is available to repair DNA damage? (1 mark)单项选择题

类似问题

Base excision, nucleotide excision and mismatch repair are strategies the cell uses to correct certain DNA mutations. Which of the following enables these repair mechanisms to occur accurately?

Which of the following statements is true of DNA damage?

Which of the following is not true about DNA double strand breaks?

Question at position 12 What binds cut DNA and retains it in protein-DNA complex?XRCC4 with DNA ligase IVKu70/80TdTArtemisRAG1/2

You have the following mutation in the DNA: What caused this mutation and how would you fix it?

Nucleotide excision repair and photolyases would be beneficial for bacterial strains _________________.

DNA repair mechanisms _______________.

Direct DNA repair may work on mutations that arise as a result of exposure to which type of chemical mutagen?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单