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16 Cards in this Set
- Front
- Back
What are the general features of a nuclear intron?
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5' end has GU
Branch Point A in the middle 3' end has AG |
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Describe the mechanism for nuclear splicing
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-U1 snRNP binds to 5' splice site
-U2 snRNP binds AROUND branch point A, not actually A (bulge) -U4/6 and U5 are recruited and bring U2 and U1 close to each other -U4 is removed to activate U6, which then replaces U1 and binds 5' splice site -transesterification between 5' end and 2' of branch point A forms lariat -U6 removed with lariat -3' end of exon attacks 3' end splice site |
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How is the lariat formed during splicing and what can be coded in it?
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-transesterification between 5' splice site and 2' OH of branch site A
-miRNA |
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What are some differences between Group I and II introns and tRNA introns?
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-Group I and II: no energy needed, self-splicing, group I uses guanine instead of adenine for transesterification while group II uses A, lead to discovery of RNA catalytic activity
-tRNA introns: endonucleases cleave both ends of introns, ATP-dep modifications then ligated exons |
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Describe enzymatic reactions to get 5' mRNA capping
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-gamma phosphate is removed from 5' end of mRNA
-guanine added 5' to 5' releasing pyrophosphate (irreversible) -methyl groups are added to last few bases |
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Describe the importance of a 5' mRNA cap
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-protects from nucleases
-increases efficiency of translation -required for export out of nucleus into cytoplasm |
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Describe enzymatic processes of adding 3' A tail
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-endonuclease cleaves between polyadenylation signal and downstream GU rich sequence
-polyadenylate polymerase adds a bunch of A's to 3' end of polyA signal |
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Describe functions of mRNA 3' polyA tail
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-Protects mRNA from exonucleases
-enhances protein synthesis by recruiting translation factors -binds polyA binding proteins (PABP) |
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List some methods of processing mRNA that will give different outcomes
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-multiple 3' splice sites
-multiple polyA sites |
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Describe rRNA processing
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-methylation and pseudouridine formation
-cleavage |
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Describe tRNA processing
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-RNaseP cuts at 5' end
-RNaseD cuts at 3' end -CCA added to 3' end (where amino acids will bind) -some base modificaitons -splicing at anticodon arm |
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Describe the general schematic of a mature mRNA
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-5' methylated G cap
-5' UTR -AUG start site -coding region -termination codon -3' UTR -3' polyA tail |
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What are the 2 mechanisms of cytoplasmic mRNA turnover?
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-deacetylation dependent decapping
-endonuclease initiated decay |
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What is a ribozyme?
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RNA molecule with catalytic capability
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what are key reactions of ribozymes?
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RNA transesterification and RNA cleavage
-substrate binds to ribozyme via base complementarity at guide sequence -ribozymes must have correct 3D shape |
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What are some examples of ribozymes?
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RNasP
Groups I and II introns hammerhead ribozymes |