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Lecture.15.Fall.2013(1) - Your Exams Are Graded But not...

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Your Exams Are Graded But not entered. You will have them back Wednesday
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RNA Molecules and Processing Translation and the Code October 21, 2013 RNA Molecules and RNA Processing Eukaryotic transcripts are extensively modified Alternative Splicing Editing tRNA structure and processing rRNA structure and processing Small RNA molecules and their functions
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RNA Molecules and Processing Translation and the Code October 21, 2013 Chapter 15: The genetic code and translation One Gene, One Enzyme Hypothesis Srb and Horowitz and arginine biosynthesis Breaking the genetic code The use of RNA polymers Degeneracy Reading frame, initiation and termination codons 59 slides in 75 minutes
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Alternative Splicing Many interrupted genes have alternative splice forms - multiple ways the pre-mRNA can be spliced Multiple proteins can be generated from a single gene Increases the diversity of the genome without increasing gene number Also used as a way to regulate biological processes ~90% of all human genes are alternatively spliced
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Example: ! -tropomyosin ! -tropomyosin is an actin-binding protein important for muscle contraction (among other things) It is extensively alternatively spliced (but not the “winner” by a long shot)
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We will be revisiting the topics of alternative splicing, promoters, and enhancers when we discuss control of eukaryotic gene expression next week.
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RNA editing The nucleotide sequence of a transcript can be changed after transcription First identified in 1986 - mRNA coding sequences are frequently different from the nuclear genes encoding them RNA editing has been found in transcripts for all types of RNA in a wide variety of organisms
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RNA editing Two basic types of RNA editing: Insertion/deletion editing: Uracil bases are added or deleted from the RNA Mediated by guide RNAs (gRNA) - template RNAs that are complementary to the edited sequence
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RNA editing Two basic types of RNA editing: Substitution editing (one nucleotide exchanged for another) A to I substitutions are the most well-known mediated by the enzyme ADAR (Adenosine Deaminase Acting on RNA)
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RNA editing RNA editing is a vital aspect of gene expression and regulation in those transcripts where it occurs ADAR mutant mice die due to nonfunctional neurotransmitter receptors that did not undergo proper mRNA editing before translation
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tRNA structure and processing tRNAs (“transfer RNAs”) are the adapter between the language of nucleic acids and the language of protein Each tRNA attaches to a single type of amino acid Most genomes encode 30 to 40 different tRNAs
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tRNA structure Cloverleaf structure, due to intramolecular base-pairing The tRNA is “charged” with an amino acid via an ester bond at the 3’ end The anticodon is complimentary to the codon specifying that amino acid As always, base-pairing is antiparallel
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Features of tRNAs Secondary and tertiary structure (see previous slide) Lots of rare, modified bases: ribothymine, pseudouridine, dozens of others These aren’t encoded in DNA; where do they come from?
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