头大
看了几个不清楚的定义把我搞混了
正确清晰的定义
https://en.wikipedia.org/wiki/Untranslated_region
和
I think there is some confusion. As Dr. Singh mentions above that the "two major divisions of DNA that are transcribed into RNA are protein-coding sections called exons, and nonprotein-coding sections called introns" is not accurate. When a mRNA is initially transcribed, often called a pre-mRNA, it contains extra information that is not present in the final mature mRNA. This extra information/RNA sequence are the introns. While they may contain information that regulates the transcription of the gene, they do not contain sequences that will be translated into the protein (as Dr. Singh correctly mentions). The exons are the sequences that will remain in the mature mRNA. However, they may contain sequences that are translated into the final protein (as Dr. Singh correctly states) or they may contain sequences that are present before and after the translated region (open reading frame), which represent the 5' and 3' untranslated sequences (UTRs). While the 5' UTR and 3' UTR are not translated, they serve important roles in maintaining the stability of the mRNA, the potential subcellular localization of the mRNA, and the regulation of the mRNA translation. Thus, the exons contain both protein-coding (translated) and non-coding (untranslated) sequences.
Also note that the transcription of all mRNAs begins and ends with an exon and introns are located between exons. Students often think that transcription begins with an intron, which contains the 5' UTR, because it is not translated. The process of removing the introns, splicing, requires specific sequences located at the exon-intron junction at the beginning of an intron and the intro-exon junction at the end of the intron. If an intron was located before the first exon or after the last exon, those spicing recognition sequences would not be entirely present and splicing would be disrupted.
总结
5' UTR，3' UTR 叫作 untranslated region ,而 introns 叫作 non-coding RNA。一段基因序列上包含外显子和内含子，转录的时候，pre-RNA就是前体RAN上会有内含子和外显子，成为成熟RNA时，内含子已经被剪切了，只保留外显子，所以内含子叫作非编码RNA（non-coding RNA）。但成熟的RNA上也是有一部分序列并不翻译成蛋白质，就是非翻译区域（untranslated region），包括上游的 5' UTR，下游的3' UTR。
上图中我们看到外显子编码的成熟RNA（coding mRNA）中，除了能翻译成蛋白质的Coding sequence（CDS）序列，5' 端还有Cap，3' 端还有 Poly-A tail 。
