Chapter 14 - Messenger RNA processing I: Splicing. In this chapter 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 Fourth Edition Chapter 14 Messenger RNA Processing I: Splicing Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Called intervening sequences, IVSs Usually called introns Parts of the gene making sense Coding regions Exons Some lower eukaryotic genes have no introns 14- Evidence for Split Genes Most higher eukaryotic genes coding for mRNA and tRNA 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 exons tRNA genes have either 0 or | Molecular Biology Fourth Edition Chapter 14 Messenger RNA Processing I: Splicing Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Called intervening sequences, IVSs Usually called introns Parts of the gene making sense Coding regions Exons Some lower eukaryotic genes have no introns 14- Evidence for Split Genes Most higher eukaryotic genes coding for mRNA and tRNA 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 exons tRNA genes have either 0 or 1 exon 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? Introns are never transcribed Polymerase somehow jumps from one exon to another Introns are transcribed Primary transcript result, an overlarge gene product is cut down by removing introns This is correct process Process of cutting introns out of immature RNAs and stitching together the exons to form final product is RNA splicing 14- Splicing Outline Introns are transcribed along with exons in the primary transcript Introns are removed as the exons are spliced together 14- Stages of RNA Splicing Messenger RNA synthesis in eukaryotes occurs in stages First stage: Synthesis of primary transcript product This is an mRNA precursor containing introns copied from the gene if present Precursor is part of a pool of large nuclear RNAs – hnRNAs Second stage: mRNA maturation Removal of introns in a process called splicing 14- .
