In chapter 14, we will see that most eukaryotic genes, in contrast to typical bacterial genes, are interrupted by noncoding DNA. RNA polymerase cannot distinguish the coding region of the gene from the noncoding regions, so it transcribes everything. | Molecular Biology Fifth Edition Chapter 14 RNA Processing I: Splicing Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mRNA Processing Events Most eukaryotic genes, in contrast to typical bacterial genes, are interrupted by noncoding DNA RNA polymerases cannot distinguish the noncoding regions from the coding regions, so it transcribes everything The cell must remove the noncoding RNA from the primary transcript via splicing Eukaryotes also add special structures to the 5’ and 3’ ends of the transcript, called the cap and poly-A tail, respectively All events occur in the nucleus before the mRNA emigrates to the cytoplasm 14- Genes in Pieces Consider the sequence of the human b-globin gene as a sentence: This is bhgty the human b-globin qwtzptlrbn gene. Two italicized regions make no sense Contain sequences unrelated to the globin coding sequences surrounding them Intervening . | Molecular Biology Fifth Edition Chapter 14 RNA Processing I: Splicing Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mRNA Processing Events Most eukaryotic genes, in contrast to typical bacterial genes, are interrupted by noncoding DNA RNA polymerases cannot distinguish the noncoding regions from the coding regions, so it transcribes everything The cell must remove the noncoding RNA from the primary transcript via splicing Eukaryotes also add special structures to the 5’ and 3’ ends of the transcript, called the cap and poly-A tail, respectively All events occur in the nucleus before the mRNA emigrates to the cytoplasm 14- Genes in Pieces Consider the sequence of the human b-globin gene as a sentence: This is bhgty the human b-globin qwtzptlrbn gene. Two italicized regions make no sense Contain sequences unrelated to the globin coding sequences surrounding them Intervening sequences, IVSs, or introns Parts of the gene making sense Coding regions or exons Some lower eukaryotic genes have no introns 14- Evidence for Split Genes Most higher eukaryotic genes coding for mRNA, tRNA and a few coding for rRNA are interrupted by unrelated regions called introns Other parts of the gene, surrounding the introns, are called exons Exons contain the sequences that finally appear in the mature RNA product Genes for mRNAs have been found with anywhere from 0 to 362 introns tRNA genes have either 0 or 1 intron 14- RNA Splicing Introns are present in genes but not in mature RNA How does the information not find its way into mature RNA products of the genes? Possibility 1: Introns are never transcribed Polymerase somehow jumps from one exon to another Possibility 2: Introns are transcribed Primary transcript result, an overlarge gene product is cut down by removing introns This is correct process The process of cutting introns out of immature RNAs and stitching together the
