1樓：羽柴殿
因為真核生物的mRNA和原核生物不一樣咯。真核生物大多是單順反子，乙個成熟mRNA就乙個開放閱讀框架ORF，只翻譯一種多肽。但是原核生物的mRNA是多順反子，乙個mRNA可能帶好幾個ORF，可以翻譯好幾種多肽
2樓：immunology111
同一種mRNA中，由於IRES的存在，也可以翻譯多種肽鏈。
同一種mRNA中，某些情況由於移碼或跳躍式翻譯，也可以出現多種肽鏈。
如果是pre-mRNA，估計通過剪接，會表達出更多種肽鏈。
3樓：雨花
轉錄完成後，產生的mRNA也不是最終形態，還要受到修飾和編輯。尤其mRNA編輯會改變核苷序列[3]，甚至直接把mRNA報廢[4]。
「Snapshot」 of a typical data set collected using targeted RNA-seq analysis of RPS12 amplicons in this study. Stacked histogram of editing events at each position in RPS12 in a representative replicate sample of RESC6-IP. The cDNA fragment examined is shown as a reference T-stripped sequence (T-str) spanning the internucleotide positions T-str 17 to 151 (see the canonical fully edited RPS12 ORF and 5′ UTR 「B-form」sequence in Supplemental Fig.
S1). A canonical editing site (ES) for uridine insertion (Ins) or deletion (Del) is just 5′ to a red or a blue non-T nucleotide, respectively. A noncanonical editing site (nES) is just 5′ to a black non-T nucleotide.
The representative histogram shows the percentage of RNA-seq reads at each position: ESs with correct insertion (red) or deletion (blue), and incorrect 「partial」 editing events (yellow). The remaining reads contain a preedited sequence.
Editing events at nESs were scored (black). nESs do not require sequence changes in mature transcripts. However, all nESs at steady state carried editing events in our samples.
The start codon (box) includes T-str positions 30–31 and requires editing at T-str 31 (ES72). The stop codon (box) includes T-st 151 (ES3) and requires editing at this position [3].
在翻譯時，有些病毒能讓核醣體跳過幾個核苷，翻譯出跟mRNA序列不一樣的肽鏈 [5, 6]。
乙個基因編碼產生的mRNA也不總是一樣的，Alternative splicing是個前沿話題，到底是不是一定產生同一種肽鏈還很難說，可能並不是。
Common mechanisms of alternative splicing. Alternative splicing can occur although a number of different processes and give rise to different mature transcripts (right). Exons and final transcripts are illustrated as boxes while lines represent introns.
Constitutively expressed exons are depicted in green, and alternatively spliced exons are depicted in blue or brown. Retained introns occur with the absence of splicing, with the intervening intron (black) included in the final transcript.[1]
一些非編碼RNA引導剪接複合體跳過一段序列，即內含子，調控訊號有很多文章論述，但仍不完全清楚[1,2]。
Exon and Intron Definition Interactions (A) Schematic of spliceosomal components and regulatory proteins that participate in exon and intron definition and interactions between them. Trans-acting splicing factors are shown as blue shapes, and their names are shown next to the shape. The RS domain is marked by 「RS.
」 Blue arrows denote intron or exon definition interactions, many of which are mediated by the RS domain. Exons are represented as gray boxes, intronic RNA and snRNAs as gray lines, and cis-acting motifs as colored lines, with the consensus sequences of these motifs shown underneath. The pairing of U1 snRNA with the 5′ splice site is indicated by black lines.
(B) Schematic of microexon definition, shown in the same manner as described in (A).
我覺得吧，中學就是學習適合中學的常識性內容，國內特別喜歡考概念辨析，我只想說清談誤國，有個了解就行了，世界上什麼東西沒有例外？但也沒必要卡在一些邊邊角角鑽牛角尖，畢竟最後會攻讀RNA方向的PhD也沒多少人。
觀其大略，把握有用資訊，是個重要的技能。"亮在荊州，以建安初與潁川石廣元、徐元直、汝南孟公威等俱遊學，三人務於精熟，而亮獨觀其大略。每晨夜從容，常抱膝長嘯，而謂三人曰：
卿諸人仕進可至郡守刺史也。三人問其所誌，亮但笑而不言。" -- 三國志-諸葛亮傳，裴松之注
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