hce_nsysu
115年
普通生物及生化概論
第 32 題
During DNA replication of an eukaryotic cell, a guanine (G) is mistakenly paired with a thymine (T) and escapes the initial proofreading by DNA polymerase. This G-T pair becomes fully incorporated into the double helix. Which of the following best describes how the cell corrects this mismatch/error?
- A The cell utilizes DNA photolyase to break the hydrogen bonds between the mismatched bases and flip them into the correct orientation.
- B The cell utilizes specific endonucleases to recognize the helical distortion and identify the newly synthesized strand to cut out the segment containing the incorrect nucleotide.
- C The cell utilizes RNA primase to recognize the mismatched sites, where it initiates reverse transcription to replace the DNA segment with a temporary RNA patch.
- D The cell utilizes DNA ligase to identify the incorrect hydrogen bonding site and uses its 5' to 3' exonuclease activity to chew back the faulty nucleotide.
- E The cell utilizes a multi-protein complex to scan the DNA for bulky lesions and remove a 12-30 nucleotide oligomer of the damaged strand.
思路引導 VIP
當 DNA 複製發生錯誤（例如兩條股上的鹼基無法正常配對）時，如果細胞直接隨機更改其中一個鹼基，可能反而會把正確的模板給改掉。請試著思考：細胞在修復時，必須具備什麼樣的「偵測能力」，才能確保自己切除的是含有錯誤資訊的那一條新股，而不是原本正確的舊模板呢？
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AI 詳解
AI 專屬家教
DNA 錯配修復機制的精準判斷
很高興看到你精確地判斷出正確答案！這題的核心在於區分細胞如何處理「複製後」才被發現的鹼基配對錯誤。當 DNA 聚合酶（DNA polymerase）的初步校對失效時，細胞會啟動錯配修復（Mismatch Repair, MMR）。你的直覺非常敏銳，正確辨識出該機制必須先區分「新合成股」與「模板股」，並利用**內切酶（Endonuclease）**在錯誤位點附近切開單股，隨後移除並重新合成該段序列，這正是選項 (B) 所描述的過程。
辨析不同修復路徑的陷阱
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