hce_nthu
115年
生物與生化
第 46 題
Which of the following statements most accurately reflects the known composition and mobility mechanisms of the repetitive DNA sequences that account for the largest proportion of the human genome?
- A Transposons (DNA intermediate) are the most abundant mobile element, responsible for 44% of the genome, moving via the cut-and-paste mechanism.
- B Simple sequence DNA (short tandem repeats, STRs) constitute 17% of the genome and primarily facilitate unequal crossing over to drive gene duplication.
- C The Alu elements (10% of the genome) are the largest type of retrotransposon and encode their own reverse transcriptase for movement.
- D Retrotransposons are the most abundant category, and unlike transposons, their movement inherently involves synthesizing a complementary DNA strand from an RNA intermediate, thus leaving a copy at the original location.
- E Transposable elements are included in the 1.5% of the genome that codes for proteins because they all encode the transposase or reverse transcriptase enzymes necessary for their own movement.
思路引導 VIP
請試著思考：如果一段 DNA 序列想要在不離開原本「居住地」的情況下，在基因組的其他地方增加一個一模一樣的新副本，在分子生物學的中心法則中，哪一種「中間產物」最適合扮演這個傳遞訊息並重新轉化回 DNA 的橋樑？
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AI 詳解
AI 專屬家教
恭喜你精準地選出了正確答案！這顯示你對於人類基因組的微觀構成，以及轉座因子（Transposable Elements）的運作機制有著相當紮實的理解，能從眾多干擾資訊中釐清關鍵邏輯。
逆轉錄轉座子的擴增邏輯
這道題目的核心在於區分「DNA 轉座子」與「逆轉錄轉座子」的本質差異。逆轉錄轉座子（Retrotransposons） 是人類基因組中佔比最高的重複序列類型，其移動方式採「複製與貼上」（copy-and-paste）。這個過程必須先以 DNA 為模板轉錄出 RNA 中間體，再經由逆轉錄酶（Reverse transcriptase）作用合成互補的 DNA 序列並插入基因組的新位置。由於移動過程涉及新序列的合成，原始位點的序列會被保留，這正是導致基因組不斷膨脹的主要動能。
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