10-31 - Mr. Burns: Damn it, Smithers! This isn't rocket...

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Mr. Burns : Damn it, Smithers! This isn't rocket science, it's brain surgery! From the Simpsons Treehouse of Horrors III The Brain : No, Pinky. Never use two drops of the formula. It would cause a reaction on the molecular level that is completely unpredictable. Pinky : Oh, I hate it when that happens. Narf.
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Announcements The most recent quiz is due this FRIDAY, Nov. 4, at noon. The CELLLS project part 1 is due Monday, Nov. 7 at 5 pm. You may work with a partner and submit a single report
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Where’s the message? Exons vs. Introns A mature mRNA does not arise from a single continuous DNA sequence, but is typically pieced together from multiple parts Exons are parts of the DNA sequence that form the mature mRNA, mainly the protein coding sequence Introns are intervening DNA sequences that do not form the mature mRNA, but may have many regulatory functions. x,y,z and hexon are exons I1, I2, and I3 are introns. Introns occur in genes coding for mRNA, tRNA, and rRNA
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Removal of introns is one form of splicing, where segments of mRNA are removed to make a mature or alternative mRNA Consensus 5’ and 3’ sequence mark splice sites and a 15-20 bp polypyrimidine (rich in C,T) also marks the 3’ end Most eukaryotic cells use spliceosomes , which are composed of proteins and catalytic RNA molecules (ribozymes)
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Summary of mRNA basic processing DNA is transcribed 5’ end is capped 3’ end polyadenylated to protect it mRNA introns are spliced out at specific regions Exons are ligated together by ligases
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Alternative splicing: the theater version versus the director’s cut “Analyses in which sequence reads are mapped to exon–exon junctions indicated that 92–94% of human genes undergo alternative splicing, 86% with a minor isoform frequency of 15% or more” -Wang et al. 2008
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Are mRNAs randomly distributed in bacteria? No! Many bacterial mRNAs stay near where they are transcribed for their lifetime. Not clear how movements are constrained Llopsis et al. 2010
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“How do I get out of here?” says the mRNA to the cell nucleus
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Detailed view of nuclear envelope Outer membrane continuous with rER. Intermembrane space continuous with rER lumen.
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10-31 - Mr. Burns: Damn it, Smithers! This isn't rocket...

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