It is transcribed in a 14 kb mRNA, and the 11kb cDNA encodes a 3685 amino acid protein of 427 kDa called Dystrophin.ĭystrophin Gene Structure. This very large gene is highly fragmented into 79 exons and introns of variable size ranging from 107 bp (intron 14) to >200kb (intron 44). The DMD gene is one of the largest known gene in humans, spanning 2.6 million base pairs (bp) consisting of almost 0.1% of the human genome or about 1.5% of the entire X chromosome. It was the study of this phenomenon that led to the discovery of ribozymes, which are enzymes made of RNA. This requires that the RNA have a specific secondary and tertiary structure, bringing the two exons close together while looping out the intron. That means for those RNAs, splicing happens autonomously, with part of the RNA acting as an enzymatic catalyst for the process. These introns are called Group I and II introns and are self-splicing! They are also present within mitochondrial and chloroplast genes. In recent years the presence of intron-containing genes has been documented in archaea, bacteriophages, and even some bacteria. Introns were initially thought to be entirely a feature of the eukaryotic genome. Splicing is the process by which the non-coding regions, known as i ntrons, are removed, and the coding regions, known as exons, are connected together. Most importantly nearly ALL mRNA precursors are spliced The immediate product of RNA polymerase II is sometimes referred to as pre-mRNA or the primary transcript.Īs we saw in Chapter 8, the initial products of transcription are further processed acquiring a cap at their 5′ end and poly-A tail at their 3′ end. You should be able to draw the pre-mRNA and mRNA derived from it. You should be able to draw /identify/annotate when given a gene sequence the elements of the gene above. These include promoters, 5′ and 3′ untranslated regions (UTR), coding sequences (exons), introns, 5′ caps, Poly A signal, and poly(A) tails. Using examples explain how anti-sense technology is used to correct for splicing defects.Ĭhapters 8 and 9 introduced you to different components of eukaryotic gene structure and RNA molecules transcribed.What are exonic and intronic splicing silencers or enhancer sequences? (ESS, ISS, ESE, and ISE).Identify when given a description/diagram of an alternately spliced gene which type it is.Draw splicing diagrams to show alternative splicing patterns.Describe the different forms/patterns of alternate splicing.Predict how mutations at the 5’ splice site, 3’ splice site, and branch point might disrupt splicing and alter the phenotype.Explain what controls the fidelity of splicing.Explain why fidelity of splicing is important?.What is transesterification, and what transesterification reactions are needed to splice introns?.Explain what are the benefits of RNA processing.Describe the roles of snRNPs in splicing.Know/draw/label the steps involved in spliceosome formation.Know the similarities and differences that exist between pre-mRNA and mRNA.
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