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16 Cards in this Set

  • Front
  • Back
What are the general features of a nuclear intron?
5' end has GU
Branch Point A in the middle
3' end has AG
Describe the mechanism for nuclear splicing
-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
How is the lariat formed during splicing and what can be coded in it?
-transesterification between 5' splice site and 2' OH of branch site A
-miRNA
What are some differences between Group I and II introns and tRNA introns?
-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
Describe enzymatic reactions to get 5' mRNA capping
-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
Describe the importance of a 5' mRNA cap
-protects from nucleases
-increases efficiency of translation
-required for export out of nucleus into cytoplasm
Describe enzymatic processes of adding 3' A tail
-endonuclease cleaves between polyadenylation signal and downstream GU rich sequence
-polyadenylate polymerase adds a bunch of A's to 3' end of polyA signal
Describe functions of mRNA 3' polyA tail
-Protects mRNA from exonucleases
-enhances protein synthesis by recruiting translation factors
-binds polyA binding proteins (PABP)
List some methods of processing mRNA that will give different outcomes
-multiple 3' splice sites
-multiple polyA sites
Describe rRNA processing
-methylation and pseudouridine formation
-cleavage
Describe tRNA processing
-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
Describe the general schematic of a mature mRNA
-5' methylated G cap
-5' UTR
-AUG start site
-coding region
-termination codon
-3' UTR
-3' polyA tail
What are the 2 mechanisms of cytoplasmic mRNA turnover?
-deacetylation dependent decapping
-endonuclease initiated decay
What is a ribozyme?
RNA molecule with catalytic capability
what are key reactions of ribozymes?
RNA transesterification and RNA cleavage
-substrate binds to ribozyme via base complementarity at guide sequence
-ribozymes must have correct 3D shape
What are some examples of ribozymes?
RNasP
Groups I and II introns
hammerhead ribozymes