文档介绍：Chapter 4 The Interrupted Gene Introduction ? interrupted gene – A gene in which the coding sequence is not continuous due to the presence of introns. ? primary (RNA) transcript – The original unmodified RNA product corresponding to a transcription unit. ? RNA splicing – The process of excising introns from RNA and connecting the exons into a continuous mRNA. Introduction ? intron – A segment of DNA that is transcribed, but later removed from within the transcript by splicing together the sequences ( exons ) on either side of it. ? mature transcript – A modified RNA transcript. Modification may include the removal of intron sequences and alterations to the 5 ′ and 3 ′ ends. FIGURE 01: Interrupted genes are expressed via a precursor RNA An Interrupted Gene Consists of Exons and Introns ? Introns are removed by RNA splicing, which occurs in cis in individual RNA molecules. ? Mutations in exons can affect polypeptide sequence; mutations in introns can affect RNA processing and hence may influence the sequence and/or production of a polypeptide. FIGURE 02: Exons remain in the same order in mRNA as in DNA, but distances along the gene do not correspond Exon and Intron positions Differ ?嘌呤和嘧啶在 DNA 中分别聚集。 A 和G倾向于在非模版链聚集。 T和C在模版链聚集。? GC 规则: GC 含量在某个物种中是特定的(在不同的基因中可以不同)。在 Exon 中的含量高于 Intron. Organization of Interrupted Genes May Be Conserved ? Introns can be detected when genes pared with their RNA transcription products by either restriction mapping, electron microscopy, or sequencing. ? cDNA – A single-stranded plementary to an RNA, synthesized from it by reverse transcription in vitro . FIGURE 03: Comparison of the restriction maps of cDNA and genomic DNA for mouse β-globin Organization of Interrupted Genes May Be Conserved ? The positions of introns are usually conserved when homologous genes pared between anisms. – The lengths of the corresponding introns may vary greatly, though. ? Introns usually do