Biochem 501: Part IV.8: RNA processing

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  1. Study of RNA processing learned which three important facts
    • Eukaryotic genes interrupted by substantial amounts of "extra" DNA (introns) of unknown function
    • RNA can act as an enzyme
    • RNA can be used as a template to generate DNA "reverse transfer of genetic information from RNA to DNA.
  2. Final RNA transcripts are ____ than the DNA template, this is because of ____
    shorter, splicing
  3. Splicing removes ____, while preserving ____
    introns, exons
  4. Splicing facts
    • -Typical gene has coding (exon) and non-coding (intron) sections.
    • -Introns compose 90% of DNA
    • -Intronic DNA is removed by splicing
    • -Splicing catalyzed by ribonucleoprotein complexes called spliceosomes
    • -Some RNA is self-splicing, these are RNA's that can act as enzymes (ribozymes)
    • -Splicing takes place in two steps: 5' releases, then attached to 3'.
  5. Splicing seen far more in
    Eukaryotes then prokaryotes
  6. Splicing can produce different ___ from same ___
    • Proteins, gene
    • Mix and match order of certain parts of the gene
  7. 4 classes of introns
    • 1. Spliceosomal introns
    • 2&3. Type I/II: self-splicing 
    • 4. tRNA introns
  8. Bacteria lack which class of intron?
  9. Steps of splicing:
    • 1. Spliceosome assembled
    •    -Made of snRNP (small ribonucleoproteins)
    • 2. Spliceosome activated
    • 3. Introns spliced
    • 4. exons joined
  10. Spliceosome composed of RNA and proteins
  11. Spliceosome RNA base pairs with RNA transcript at:
    intron-exon boundaries
  12. Chemistry of splicing
    • 3. OH on intron attacks phosphodiester bond on end of exon 1 (first transesterification)
    • 4. OH now at end of exon 1 attacks phosphodiester bond between intron and exon 2
    • 5. exons now connected by a phosphodiester bond. Intron is now an excised lariat intron.
  13. Self-splicing introns
    • Type I:
    • Rely on exogenous guanosine
    • G docks to 5' end of intron  (transesterification)
    • New OH on 5' end attacks 3' end of exon (transesterification)
    • Type II: First attack comes from OH on adenosine in intron
  14. Differences between Type I/II introns:
    • Type I: Relies of exogenous guanine to begin first attack
    • Type II: Relies on internal adenosine to begin first attack.
  15. rRNA/tRNA usually synthesized as:
    Extened transcripts that are cut at precise locations to generate functional molecules
  16. Nuclease that cleaves tRNA out
    RnaseR (ribonucleoprotein) (RNA is catalytic subunit).
  17. Eukaryotic mRNA 5'/3' ends are modified:
  18. mRNA 5' end modification
    • Eukaryotic mRNAs have 7-methyl guanosine "cap" added to the 5' end.
    • Cap aids in forming the translation initiation complex and protects the 5' end from degradation.
  19. 5' end caps added by
    • RNA Pol II
    • (Capping enzyme (CE), RNA methyltransferase (RNMT), protein involved in translation (elF4E)
  20. 3' ends of mRNA are:
    • cleaved and polyadenylated (polyA tails)
    •      -signals nuclear export
    •      -stabilizes mRNA
    •      -promotes translation
  21. Reverse flow of genetic info:
    • Retroviruses
    • Carry RNA "genes", transfer genetic material to DNA after infection
    • Reverse transcriptase generates double-standard DNA from RNA
    • Reverse transcriptase also found in uninfected cells
  22. Discovered reverse transcriptase for nobel prize
    Howard Temin
  23. Reverse transcriptase is a:
    DNA polymerase
  24. Telomerase:
    • keeps chromosome tips from degrading
    • Is a reverse transcriptase, RNA catalytic core
    • Uses RNA base to add back the bits of telomere that are removed with each replication
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Biochem 501: Part IV.8: RNA processing
2013-12-06 19:57:52
Biochem 501

Biochem 501
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