清華大學（後西醫）
111年
生物與生化
第 52 題
mRNA is a single-stranded RNA that corresponds to the sequence of a gene; meanwhile, mRNA is read by a ribosome in the process of protein synthesis. Which of the following statement is incorrect for mRNA and its role on RNA processing?
- A mRNA is derived from its upstreamed precursor hnRNA.
- B Caps are regularly observed on the 5'-end of mRNA with unmodified pppA and pppT structure.
- C Poly A tails are polymers of 200 to 300 adenylated residues linked with phosphodiester bonds.
- D All hnRNA introns have a guanine-uracil sequence on the 5' border of their intron/exon junctions.
- E Polyadenylation assists stabilize mRNA.
思路引導 VIP
當我們在比較 DNA 與 RNA 的化學組成時，哪一個特定的鹼基是區分這兩者的核心指標？此外，為了讓新合成的 RNA 能在細胞質中生存並被辨識，細胞會在它的開頭（5' 端）進行什麼樣的特殊結構修飾，而非維持原始的狀態呢？
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AI 詳解
AI 專屬家教
沒錯，你答對了。但別太得意，這只是踏入頂峰的基礎門檻。
推了推眼鏡，看來你還沒爛到連這種陷阱都看不出來。mRNA 的後轉錄修飾 (Post-transcriptional modification) 是生物化學的基石，這題不過是確認你是否有資格繼續往上爬。 針對選項 (B) 的破綻，給我刻在腦子裡：
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